Code of "GCNet: Non-local Networks Meet Squeeze-Excitation Networks and Beyond" (#598)

* add pytorch 1.1.0 SyncBN support

* change BatchNorm2d to _BatchNorm and call freeze after train

* add freeze back to init function

* fixed indentation typo in adding freeze

* convert SyncBN to BN when eval is called

* add gcb and configs

* fixed line too long

* fixed space and newline

* ignore too long line in config files

* two space before inline comment

* refactor var name

* fixed line too long

* changed SyncBN to backbone only and add non-Sync BN configs

* reformat config to adapt master branch

* reformat change method->type

* remoe some configs

* clean up readme.md

* add benchmark

* fix typo in README

* change sbn to syncbn

* change work dir

* refactor gcb

* fixed line too long

* Code formatting

configs/gcnet/README.md

+# GCNet for Object Detection
+
+By [Yue Cao](http://yue-cao.me), [Jiarui Xu](http://jerryxu.net), [Stephen Lin](https://scholar.google.com/citations?user=c3PYmxUAAAAJ&hl=en), Fangyun Wei, [Han Hu](https://sites.google.com/site/hanhushomepage/).
+
+We provide config files to reproduce the results in the paper for
+["GCNet: Non-local Networks Meet Squeeze-Excitation Networks and Beyond"](https://arxiv.org/abs/1904.11492) on COCO object detection.
+
+## Introduction
+
+**GCNet** is initially described in [arxiv](https://arxiv.org/abs/1904.11492). Via absorbing advantages of Non-Local Networks (NLNet) and Squeeze-Excitation Networks (SENet),  GCNet provides a simple, fast and effective approach for global context modeling, which generally outperforms both NLNet and SENet on major benchmarks for various recognition tasks.
+
+## Citing GCNet
+
+```
+@article{cao2019GCNet,
+  title={GCNet: Non-local Networks Meet Squeeze-Excitation Networks and Beyond},
+  author={Cao, Yue and Xu, Jiarui and Lin, Stephen and Wei, Fangyun and Hu, Han},
+  journal={arXiv preprint arXiv:1904.11492},
+  year={2019}
+}
+```
+
+## Results and models
+The results on COCO 2017val are shown in the below table.
+
+| Backbone  | Model            | Context        | Lr schd | Mem (GB) | Train time (s/iter) | Inf time (fps) | box AP | mask AP | Download  |
+| :-------: | :--------------: | :------------: | :-----: | :------: | :-----------------: | :------------: | :----: | :-----: | :-------: |
+| R-50-FPN  | Mask             | GC(c3-c5, r16) |   1x    | 4.5      | 0.533              | 10.1           | 38.5   |  35.1   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/mask_rcnn_r16_gcb_c3-c5_r50_fpn_1x_20190602-c550c707.pth) |
+| R-50-FPN  | Mask             | GC(c3-c5, r4)  |   1x    | 4.6      | 0.533              | 9.9            | 38.9   |  35.5   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/mask_rcnn_r4_gcb_c3-c5_r50_fpn_1x_20190602-18ae2dfd.pth) |
+| R-101-FPN | Mask             | GC(c3-c5, r16) |   1x    | 7.0      | 0.731              | 8.6            | 40.8   |  37.0   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/mask_rcnn_r16_gcb_c3-c5_r101_fpn_1x_20190602-f4456442.pth) |
+| R-101-FPN | Mask             | GC(c3-c5, r4)  |   1x    | 7.1      | 0.747              | 8.6            | 40.8   |  36.9   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/mask_rcnn_r4_gcb_c3-c5_r101_fpn_1x_20190602-1ee20d5f.pth) |
+
+| Backbone  | Model            | Context        | Lr schd | Mem (GB) | Train time (s/iter) | Inf time (fps) | box AP | mask AP | Download  |
+| :-------: | :--------------: | :------------: | :-----: | :------: | :-----------------: | :------------: | :----: | :-----: | :-------: |
+| R-50-FPN  | Mask             |      -         |   1x    | 3.9      | 0.543              | 10.2           | 37.2   |  33.8   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/mask_rcnn_r50_fpn_syncbn_1x_20190602-bccc62fa.pth) |
+| R-50-FPN  | Mask             | GC(c3-c5, r16) |   1x    | 4.5      | 0.547              | 9.9            | 39.4   |  35.7   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/mask_rcnn_r16_gcb_c3-c5_r50_fpn_syncbn_1x_20190602-a0169c20.pth) |
+| R-50-FPN  | Mask             | GC(c3-c5, r4)  |   1x    | 4.6      | 0.603              | 9.4            | 39.9   |  36.2   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/mask_rcnn_r4_gcb_c3-c5_r50_fpn_syncbn_1x_20190602-ace08792.pth) |
+| R-101-FPN | Mask             |      -         |   1x    | 5.8      | 0.665              | 9.2            | 39.8   |  36.0   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/mask_rcnn_r101_fpn_syncbn_1x_20190602-b2a0e2b7.pth) |
+| R-101-FPN | Mask             | GC(c3-c5, r16) |   1x    | 7.0      | 0.778              | 9.0            | 41.1   |  37.4   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/mask_rcnn_r16_gcb_c3-c5_r101_fpn_syncbn_1x_20190602-717e6dbd.pth) |
+| R-101-FPN | Mask             | GC(c3-c5, r4)  |   1x    | 7.1      | 0.786              | 8.9            | 41.7   |  37.6   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/mask_rcnn_r4_gcb_c3-c5_r101_fpn_syncbn_1x_20190602-a893c718.pth) |
+| X-101-FPN | Mask             |      -         |   1x    | 7.1      | 0.912              | 8.5            | 41.2   |  37.3   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/mask_rcnn_x101_32x4d_fpn_syncbn_1x_20190602-bb8ae7e5.pth) |
+| X-101-FPN | Mask             | GC(c3-c5, r16) |   1x    | 8.2      | 1.055              | 7.7            | 42.4   |  38.0   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/mask_rcnn_r16_gcb_c3-c5_x101_32x4d_fpn_syncbn_1x_20190602-c28edb53.pth) |
+| X-101-FPN | Mask             | GC(c3-c5, r4)  |   1x    | 8.3      | 1.037              | 7.6            | 42.9   |  38.5   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/mask_rcnn_r4_gcb_c3-c5_x101_32x4d_fpn_syncbn_1x_20190602-930b3d51.pth) |
+| X-101-FPN | Cascade Mask     |      -         |   1x    | -        | -                  | -              | 44.7   |  38.3   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/cascade_mask_rcnn_x101_32x4d_fpn_syncbn_1x_20190602-63a800fb.pth) |
+| X-101-FPN | Cascade Mask     | GC(c3-c5, r16) |   1x    | -        | -                  | -              | 45.9   |  39.3   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/cascade_mask_rcnn_r16_gcb_c3-c5_x101_32x4d_fpn_syncbn_1x_20190602-3e168d88.pth) |
+| X-101-FPN | Cascade Mask     | GC(c3-c5, r4)  |   1x    | -        | -                  | -              | 46.5   |  39.7   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/cascade_mask_rcnn_r4_gcb_c3-c5_x101_32x4d_fpn_syncbn_1x_20190602-b579157f.pth) |
+| X-101-FPN | DCN Cascade Mask |      -         |   1x    | -        | -                  | -              | 47.1   |  40.4   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/cascade_mask_rcnn_dconv_c3-c5_x101_32x4d_fpn_syncbn_1x_20190602-9aa8c394.pth) |
+| X-101-FPN | DCN Cascade Mask | GC(c3-c5, r16) |   1x    | -        | -                  | -              | 47.9   |  40.9   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/cascade_mask_rcnn_r16_gcb_dconv_c3-c5_x101_32x4d_fpn_syncbn_1x_20190602-b86027a6.pth) |
+| X-101-FPN | DCN Cascade Mask | GC(c3-c5, r4)  |   1x    | -        | -                  | -              | 47.9   |  40.8   | [model](https://open-mmlab.s3.ap-northeast-2.amazonaws.com/mmdetection/models/gcnet/cascade_mask_rcnn_r4_gcb_dconv_c3-c5_x101_32x4d_fpn_syncbn_1x_20190602-b4164f6b.pth) |
+
+
+**Notes:**
+
+- The `SyncBN` is added in the backbone for all models in **Table 2**.
+- `GC` denotes Global Context (GC) block is inserted after 1x1 conv of backbone.
+- `DCN` denotes replace 3x3 conv with 3x3 Deformable Convolution in `c3-c5` stages of backbone.
+- `r4` and `r16` denote ratio 4 and ratio 16 in GC block respectively.
+

configs/gcnet/mask_rcnn_r16_gcb_c3-c5_r50_fpn_1x.py

+# model settings
+model = dict(
+    type='MaskRCNN',
+    pretrained='modelzoo://resnet50',
+    backbone=dict(
+        type='ResNet',
+        depth=50,
+        num_stages=4,
+        out_indices=(0, 1, 2, 3),
+        frozen_stages=1,
+        style='pytorch',
+        gcb=dict(
+            ratio=1./16.,
+        ),
+        stage_with_gcb=(False, True, True, True)),
+    neck=dict(
+        type='FPN',
+        in_channels=[256, 512, 1024, 2048],
+        out_channels=256,
+        num_outs=5),
+    rpn_head=dict(
+        type='RPNHead',
+        in_channels=256,
+        feat_channels=256,
+        anchor_scales=[8],
+        anchor_ratios=[0.5, 1.0, 2.0],
+        anchor_strides=[4, 8, 16, 32, 64],
+        target_means=[.0, .0, .0, .0],
+        target_stds=[1.0, 1.0, 1.0, 1.0],
+        loss_cls=dict(
+            type='CrossEntropyLoss', use_sigmoid=True, loss_weight=1.0),
+        loss_bbox=dict(type='SmoothL1Loss', beta=1.0 / 9.0, loss_weight=1.0)),
+    bbox_roi_extractor=dict(
+        type='SingleRoIExtractor',
+        roi_layer=dict(type='RoIAlign', out_size=7, sample_num=2),
+        out_channels=256,
+        featmap_strides=[4, 8, 16, 32]),
+    bbox_head=dict(
+        type='SharedFCBBoxHead',
+        num_fcs=2,
+        in_channels=256,
+        fc_out_channels=1024,
+        roi_feat_size=7,
+        num_classes=81,
+        target_means=[0., 0., 0., 0.],
+        target_stds=[0.1, 0.1, 0.2, 0.2],
+        reg_class_agnostic=False,
+        loss_cls=dict(
+            type='CrossEntropyLoss', use_sigmoid=False, loss_weight=1.0),
+        loss_bbox=dict(type='SmoothL1Loss', beta=1.0, loss_weight=1.0)),
+    mask_roi_extractor=dict(
+        type='SingleRoIExtractor',
+        roi_layer=dict(type='RoIAlign', out_size=14, sample_num=2),
+        out_channels=256,
+        featmap_strides=[4, 8, 16, 32]),
+    mask_head=dict(
+        type='FCNMaskHead',
+        num_convs=4,
+        in_channels=256,
+        conv_out_channels=256,
+        num_classes=81,
+        loss_mask=dict(
+            type='CrossEntropyLoss', use_mask=True, loss_weight=1.0)))
+# model training and testing settings
+train_cfg = dict(
+    rpn=dict(
+        assigner=dict(
+            type='MaxIoUAssigner',
+            pos_iou_thr=0.7,
+            neg_iou_thr=0.3,
+            min_pos_iou=0.3,
+            ignore_iof_thr=-1),
+        sampler=dict(
+            type='RandomSampler',
+            num=256,
+            pos_fraction=0.5,
+            neg_pos_ub=-1,
+            add_gt_as_proposals=False),
+        allowed_border=0,
+        pos_weight=-1,
+        debug=False),
+    rpn_proposal=dict(
+        nms_across_levels=False,
+        nms_pre=2000,
+        nms_post=2000,
+        max_num=2000,
+        nms_thr=0.7,
+        min_bbox_size=0),
+    rcnn=dict(
+        assigner=dict(
+            type='MaxIoUAssigner',
+            pos_iou_thr=0.5,
+            neg_iou_thr=0.5,
+            min_pos_iou=0.5,
+            ignore_iof_thr=-1),
+        sampler=dict(
+            type='RandomSampler',
+            num=512,
+            pos_fraction=0.25,
+            neg_pos_ub=-1,
+            add_gt_as_proposals=True),
+        mask_size=28,
+        pos_weight=-1,
+        debug=False))
+test_cfg = dict(
+    rpn=dict(
+        nms_across_levels=False,
+        nms_pre=1000,
+        nms_post=1000,
+        max_num=1000,
+        nms_thr=0.7,
+        min_bbox_size=0),
+    rcnn=dict(
+        score_thr=0.05,
+        nms=dict(type='nms', iou_thr=0.5),
+        max_per_img=100,
+        mask_thr_binary=0.5))
+# dataset settings
+dataset_type = 'CocoDataset'
+data_root = 'data/coco/'
+img_norm_cfg = dict(
+    mean=[123.675, 116.28, 103.53], std=[58.395, 57.12, 57.375], to_rgb=True)
+data = dict(
+    imgs_per_gpu=2,
+    workers_per_gpu=2,
+    train=dict(
+        type=dataset_type,
+        ann_file=data_root + 'annotations/instances_train2017.json',
+        img_prefix=data_root + 'train2017/',
+        img_scale=(1333, 800),
+        img_norm_cfg=img_norm_cfg,
+        size_divisor=32,
+        flip_ratio=0.5,
+        with_mask=True,
+        with_crowd=True,
+        with_label=True),
+    val=dict(
+        type=dataset_type,
+        ann_file=data_root + 'annotations/instances_val2017.json',
+        img_prefix=data_root + 'val2017/',
+        img_scale=(1333, 800),
+        img_norm_cfg=img_norm_cfg,
+        size_divisor=32,
+        flip_ratio=0,
+        with_mask=True,
+        with_crowd=True,
+        with_label=True),
+    test=dict(
+        type=dataset_type,
+        ann_file=data_root + 'annotations/instances_val2017.json',
+        img_prefix=data_root + 'val2017/',
+        img_scale=(1333, 800),
+        img_norm_cfg=img_norm_cfg,
+        size_divisor=32,
+        flip_ratio=0,
+        with_mask=False,
+        with_label=False,
+        test_mode=True))
+# optimizer
+optimizer = dict(type='SGD', lr=0.02, momentum=0.9, weight_decay=0.0001)
+optimizer_config = dict(grad_clip=dict(max_norm=35, norm_type=2))
+# learning policy
+lr_config = dict(
+    policy='step',
+    warmup='linear',
+    warmup_iters=500,
+    warmup_ratio=1.0 / 3,
+    step=[8, 11])
+checkpoint_config = dict(interval=1)
+# yapf:disable
+log_config = dict(
+    interval=50,
+    hooks=[
+        dict(type='TextLoggerHook'),
+        # dict(type='TensorboardLoggerHook')
+    ])
+# yapf:enable
+# runtime settings
+total_epochs = 12
+dist_params = dict(backend='nccl')
+log_level = 'INFO'
+work_dir = './work_dirs/mask_rcnn_r16_gcb_c3-c5_r50_fpn_1x'
+load_from = None
+resume_from = None
+workflow = [('train', 1)]

configs/gcnet/mask_rcnn_r16_gcb_c3-c5_r50_fpn_syncbn_1x.py

+# model settings
+norm_cfg = dict(type='SyncBN', requires_grad=True)
+
+model = dict(
+    type='MaskRCNN',
+    pretrained='modelzoo://resnet50',
+    backbone=dict(
+        type='ResNet',
+        depth=50,
+        num_stages=4,
+        out_indices=(0, 1, 2, 3),
+        frozen_stages=1,
+        style='pytorch',
+        gcb=dict(
+            ratio=1./16.,
+        ),
+        stage_with_gcb=(False, True, True, True),
+        norm_eval=False,
+        norm_cfg=norm_cfg),
+    neck=dict(
+        type='FPN',
+        in_channels=[256, 512, 1024, 2048],
+        out_channels=256,
+        num_outs=5),
+    rpn_head=dict(
+        type='RPNHead',
+        in_channels=256,
+        feat_channels=256,
+        anchor_scales=[8],
+        anchor_ratios=[0.5, 1.0, 2.0],
+        anchor_strides=[4, 8, 16, 32, 64],
+        target_means=[.0, .0, .0, .0],
+        target_stds=[1.0, 1.0, 1.0, 1.0],
+        loss_cls=dict(
+            type='CrossEntropyLoss', use_sigmoid=True, loss_weight=1.0),
+        loss_bbox=dict(type='SmoothL1Loss', beta=1.0 / 9.0, loss_weight=1.0)),
+    bbox_roi_extractor=dict(
+        type='SingleRoIExtractor',
+        roi_layer=dict(type='RoIAlign', out_size=7, sample_num=2),
+        out_channels=256,
+        featmap_strides=[4, 8, 16, 32]),
+    bbox_head=dict(
+        type='SharedFCBBoxHead',
+        num_fcs=2,
+        in_channels=256,
+        fc_out_channels=1024,
+        roi_feat_size=7,
+        num_classes=81,
+        target_means=[0., 0., 0., 0.],
+        target_stds=[0.1, 0.1, 0.2, 0.2],
+        reg_class_agnostic=False,
+        loss_cls=dict(
+            type='CrossEntropyLoss', use_sigmoid=False, loss_weight=1.0),
+        loss_bbox=dict(type='SmoothL1Loss', beta=1.0, loss_weight=1.0)),
+    mask_roi_extractor=dict(
+        type='SingleRoIExtractor',
+        roi_layer=dict(type='RoIAlign', out_size=14, sample_num=2),
+        out_channels=256,
+        featmap_strides=[4, 8, 16, 32]),
+    mask_head=dict(
+        type='FCNMaskHead',
+        num_convs=4,
+        in_channels=256,
+        conv_out_channels=256,
+        num_classes=81,
+        loss_mask=dict(
+            type='CrossEntropyLoss', use_mask=True, loss_weight=1.0)))
+# model training and testing settings
+train_cfg = dict(
+    rpn=dict(
+        assigner=dict(
+            type='MaxIoUAssigner',
+            pos_iou_thr=0.7,
+            neg_iou_thr=0.3,
+            min_pos_iou=0.3,
+            ignore_iof_thr=-1),
+        sampler=dict(
+            type='RandomSampler',
+            num=256,
+            pos_fraction=0.5,
+            neg_pos_ub=-1,
+            add_gt_as_proposals=False),
+        allowed_border=0,
+        pos_weight=-1,
+        debug=False),
+    rpn_proposal=dict(
+        nms_across_levels=False,
+        nms_pre=2000,
+        nms_post=2000,
+        max_num=2000,
+        nms_thr=0.7,
+        min_bbox_size=0),
+    rcnn=dict(
+        assigner=dict(
+            type='MaxIoUAssigner',
+            pos_iou_thr=0.5,
+            neg_iou_thr=0.5,
+            min_pos_iou=0.5,
+            ignore_iof_thr=-1),
+        sampler=dict(
+            type='RandomSampler',
+            num=512,
+            pos_fraction=0.25,
+            neg_pos_ub=-1,
+            add_gt_as_proposals=True),
+        mask_size=28,
+        pos_weight=-1,
+        debug=False))
+test_cfg = dict(
+    rpn=dict(
+        nms_across_levels=False,
+        nms_pre=1000,
+        nms_post=1000,
+        max_num=1000,
+        nms_thr=0.7,
+        min_bbox_size=0),
+    rcnn=dict(
+        score_thr=0.05,
+        nms=dict(type='nms', iou_thr=0.5),
+        max_per_img=100,
+        mask_thr_binary=0.5))
+# dataset settings
+dataset_type = 'CocoDataset'
+data_root = 'data/coco/'
+img_norm_cfg = dict(
+    mean=[123.675, 116.28, 103.53], std=[58.395, 57.12, 57.375], to_rgb=True)
+data = dict(
+    imgs_per_gpu=2,
+    workers_per_gpu=2,
+    train=dict(
+        type=dataset_type,
+        ann_file=data_root + 'annotations/instances_train2017.json',
+        img_prefix=data_root + 'train2017/',
+        img_scale=(1333, 800),
+        img_norm_cfg=img_norm_cfg,
+        size_divisor=32,
+        flip_ratio=0.5,
+        with_mask=True,
+        with_crowd=True,
+        with_label=True),
+    val=dict(
+        type=dataset_type,
+        ann_file=data_root + 'annotations/instances_val2017.json',
+        img_prefix=data_root + 'val2017/',
+        img_scale=(1333, 800),
+        img_norm_cfg=img_norm_cfg,
+        size_divisor=32,
+        flip_ratio=0,
+        with_mask=True,
+        with_crowd=True,
+        with_label=True),
+    test=dict(
+        type=dataset_type,
+        ann_file=data_root + 'annotations/instances_val2017.json',
+        img_prefix=data_root + 'val2017/',
+        img_scale=(1333, 800),
+        img_norm_cfg=img_norm_cfg,
+        size_divisor=32,
+        flip_ratio=0,
+        with_mask=False,
+        with_label=False,
+        test_mode=True))
+# optimizer
+optimizer = dict(type='SGD', lr=0.02, momentum=0.9, weight_decay=0.0001)
+optimizer_config = dict(grad_clip=dict(max_norm=35, norm_type=2))
+# learning policy
+lr_config = dict(
+    policy='step',
+    warmup='linear',
+    warmup_iters=500,
+    warmup_ratio=1.0 / 3,
+    step=[8, 11])
+checkpoint_config = dict(interval=1)
+# yapf:disable
+log_config = dict(
+    interval=50,
+    hooks=[
+        dict(type='TextLoggerHook'),
+        # dict(type='TensorboardLoggerHook')
+    ])
+# yapf:enable
+# runtime settings
+total_epochs = 12
+dist_params = dict(backend='nccl')
+log_level = 'INFO'
+work_dir = './work_dirs/mask_rcnn_r16_gcb_c3-c5_r50_fpn_syncbn_1x'
+load_from = None
+resume_from = None
+workflow = [('train', 1)]

configs/gcnet/mask_rcnn_r4_gcb_c3-c5_r50_fpn_1x.py

+# model settings
+model = dict(
+    type='MaskRCNN',
+    pretrained='modelzoo://resnet50',
+    backbone=dict(
+        type='ResNet',
+        depth=50,
+        num_stages=4,
+        out_indices=(0, 1, 2, 3),
+        frozen_stages=1,
+        style='pytorch',
+        gcb=dict(
+            ratio=1./4.,
+        ),
+        stage_with_gcb=(False, True, True, True)),
+    neck=dict(
+        type='FPN',
+        in_channels=[256, 512, 1024, 2048],
+        out_channels=256,
+        num_outs=5),
+    rpn_head=dict(
+        type='RPNHead',
+        in_channels=256,
+        feat_channels=256,
+        anchor_scales=[8],
+        anchor_ratios=[0.5, 1.0, 2.0],
+        anchor_strides=[4, 8, 16, 32, 64],
+        target_means=[.0, .0, .0, .0],
+        target_stds=[1.0, 1.0, 1.0, 1.0],
+        loss_cls=dict(
+            type='CrossEntropyLoss', use_sigmoid=True, loss_weight=1.0),
+        loss_bbox=dict(type='SmoothL1Loss', beta=1.0 / 9.0, loss_weight=1.0)),
+    bbox_roi_extractor=dict(
+        type='SingleRoIExtractor',
+        roi_layer=dict(type='RoIAlign', out_size=7, sample_num=2),
+        out_channels=256,
+        featmap_strides=[4, 8, 16, 32]),
+    bbox_head=dict(
+        type='SharedFCBBoxHead',
+        num_fcs=2,
+        in_channels=256,
+        fc_out_channels=1024,
+        roi_feat_size=7,
+        num_classes=81,
+        target_means=[0., 0., 0., 0.],
+        target_stds=[0.1, 0.1, 0.2, 0.2],
+        reg_class_agnostic=False,
+        loss_cls=dict(
+            type='CrossEntropyLoss', use_sigmoid=False, loss_weight=1.0),
+        loss_bbox=dict(type='SmoothL1Loss', beta=1.0, loss_weight=1.0)),
+    mask_roi_extractor=dict(
+        type='SingleRoIExtractor',
+        roi_layer=dict(type='RoIAlign', out_size=14, sample_num=2),
+        out_channels=256,
+        featmap_strides=[4, 8, 16, 32]),
+    mask_head=dict(
+        type='FCNMaskHead',
+        num_convs=4,
+        in_channels=256,
+        conv_out_channels=256,
+        num_classes=81,
+        loss_mask=dict(
+            type='CrossEntropyLoss', use_mask=True, loss_weight=1.0)))
+# model training and testing settings
+train_cfg = dict(
+    rpn=dict(
+        assigner=dict(
+            type='MaxIoUAssigner',
+            pos_iou_thr=0.7,
+            neg_iou_thr=0.3,
+            min_pos_iou=0.3,
+            ignore_iof_thr=-1),
+        sampler=dict(
+            type='RandomSampler',
+            num=256,
+            pos_fraction=0.5,
+            neg_pos_ub=-1,
+            add_gt_as_proposals=False),
+        allowed_border=0,
+        pos_weight=-1,
+        debug=False),
+    rpn_proposal=dict(
+        nms_across_levels=False,
+        nms_pre=2000,
+        nms_post=2000,
+        max_num=2000,
+        nms_thr=0.7,
+        min_bbox_size=0),
+    rcnn=dict(
+        assigner=dict(
+            type='MaxIoUAssigner',
+            pos_iou_thr=0.5,
+            neg_iou_thr=0.5,
+            min_pos_iou=0.5,
+            ignore_iof_thr=-1),
+        sampler=dict(
+            type='RandomSampler',
+            num=512,
+            pos_fraction=0.25,
+            neg_pos_ub=-1,
+            add_gt_as_proposals=True),
+        mask_size=28,
+        pos_weight=-1,
+        debug=False))
+test_cfg = dict(
+    rpn=dict(
+        nms_across_levels=False,
+        nms_pre=1000,
+        nms_post=1000,
+        max_num=1000,
+        nms_thr=0.7,
+        min_bbox_size=0),
+    rcnn=dict(
+        score_thr=0.05,
+        nms=dict(type='nms', iou_thr=0.5),
+        max_per_img=100,
+        mask_thr_binary=0.5))
+# dataset settings
+dataset_type = 'CocoDataset'
+data_root = 'data/coco/'
+img_norm_cfg = dict(
+    mean=[123.675, 116.28, 103.53], std=[58.395, 57.12, 57.375], to_rgb=True)
+data = dict(
+    imgs_per_gpu=2,
+    workers_per_gpu=2,
+    train=dict(
+        type=dataset_type,
+        ann_file=data_root + 'annotations/instances_train2017.json',
+        img_prefix=data_root + 'train2017/',
+        img_scale=(1333, 800),
+        img_norm_cfg=img_norm_cfg,
+        size_divisor=32,
+        flip_ratio=0.5,
+        with_mask=True,
+        with_crowd=True,
+        with_label=True),
+    val=dict(
+        type=dataset_type,
+        ann_file=data_root + 'annotations/instances_val2017.json',
+        img_prefix=data_root + 'val2017/',
+        img_scale=(1333, 800),
+        img_norm_cfg=img_norm_cfg,
+        size_divisor=32,
+        flip_ratio=0,
+        with_mask=True,
+        with_crowd=True,
+        with_label=True),
+    test=dict(
+        type=dataset_type,
+        ann_file=data_root + 'annotations/instances_val2017.json',
+        img_prefix=data_root + 'val2017/',
+        img_scale=(1333, 800),
+        img_norm_cfg=img_norm_cfg,
+        size_divisor=32,
+        flip_ratio=0,
+        with_mask=False,
+        with_label=False,
+        test_mode=True))
+# optimizer
+optimizer = dict(type='SGD', lr=0.02, momentum=0.9, weight_decay=0.0001)
+optimizer_config = dict(grad_clip=dict(max_norm=35, norm_type=2))
+# learning policy
+lr_config = dict(
+    policy='step',
+    warmup='linear',
+    warmup_iters=500,
+    warmup_ratio=1.0 / 3,
+    step=[8, 11])
+checkpoint_config = dict(interval=1)
+# yapf:disable
+log_config = dict(
+    interval=50,
+    hooks=[
+        dict(type='TextLoggerHook'),
+        # dict(type='TensorboardLoggerHook')
+    ])
+# yapf:enable
+# runtime settings
+total_epochs = 12
+dist_params = dict(backend='nccl')
+log_level = 'INFO'
+work_dir = './work_dirs/mask_rcnn_r4_gcb_c3-c5_r50_fpn_1x'
+load_from = None
+resume_from = None
+workflow = [('train', 1)]

configs/gcnet/mask_rcnn_r4_gcb_c3-c5_r50_fpn_syncbn_1x.py

+# model settings
+norm_cfg = dict(type='SyncBN', requires_grad=True)
+
+model = dict(
+    type='MaskRCNN',
+    pretrained='modelzoo://resnet50',
+    backbone=dict(
+        type='ResNet',
+        depth=50,
+        num_stages=4,
+        out_indices=(0, 1, 2, 3),
+        frozen_stages=1,
+        style='pytorch',
+        gcb=dict(
+            ratio=1./4.,
+        ),
+        stage_with_gcb=(False, True, True, True),
+        norm_eval=False,
+        norm_cfg=norm_cfg),
+    neck=dict(
+        type='FPN',
+        in_channels=[256, 512, 1024, 2048],
+        out_channels=256,
+        num_outs=5),
+    rpn_head=dict(
+        type='RPNHead',
+        in_channels=256,
+        feat_channels=256,
+        anchor_scales=[8],
+        anchor_ratios=[0.5, 1.0, 2.0],
+        anchor_strides=[4, 8, 16, 32, 64],
+        target_means=[.0, .0, .0, .0],
+        target_stds=[1.0, 1.0, 1.0, 1.0],
+        loss_cls=dict(
+            type='CrossEntropyLoss', use_sigmoid=True, loss_weight=1.0),
+        loss_bbox=dict(type='SmoothL1Loss', beta=1.0 / 9.0, loss_weight=1.0)),
+    bbox_roi_extractor=dict(
+        type='SingleRoIExtractor',
+        roi_layer=dict(type='RoIAlign', out_size=7, sample_num=2),
+        out_channels=256,
+        featmap_strides=[4, 8, 16, 32]),
+    bbox_head=dict(
+        type='SharedFCBBoxHead',
+        num_fcs=2,
+        in_channels=256,
+        fc_out_channels=1024,
+        roi_feat_size=7,
+        num_classes=81,
+        target_means=[0., 0., 0., 0.],
+        target_stds=[0.1, 0.1, 0.2, 0.2],
+        reg_class_agnostic=False,
+        loss_cls=dict(
+            type='CrossEntropyLoss', use_sigmoid=False, loss_weight=1.0),
+        loss_bbox=dict(type='SmoothL1Loss', beta=1.0, loss_weight=1.0)),
+    mask_roi_extractor=dict(
+        type='SingleRoIExtractor',
+        roi_layer=dict(type='RoIAlign', out_size=14, sample_num=2),
+        out_channels=256,
+        featmap_strides=[4, 8, 16, 32]),
+    mask_head=dict(
+        type='FCNMaskHead',
+        num_convs=4,
+        in_channels=256,
+        conv_out_channels=256,
+        num_classes=81,
+        loss_mask=dict(
+            type='CrossEntropyLoss', use_mask=True, loss_weight=1.0)))
+# model training and testing settings
+train_cfg = dict(
+    rpn=dict(
+        assigner=dict(
+            type='MaxIoUAssigner',
+            pos_iou_thr=0.7,
+            neg_iou_thr=0.3,
+            min_pos_iou=0.3,
+            ignore_iof_thr=-1),
+        sampler=dict(
+            type='RandomSampler',
+            num=256,
+            pos_fraction=0.5,
+            neg_pos_ub=-1,
+            add_gt_as_proposals=False),
+        allowed_border=0,
+        pos_weight=-1,
+        debug=False),
+    rpn_proposal=dict(
+        nms_across_levels=False,
+        nms_pre=2000,
+        nms_post=2000,
+        max_num=2000,
+        nms_thr=0.7,
+        min_bbox_size=0),
+    rcnn=dict(
+        assigner=dict(
+            type='MaxIoUAssigner',
+            pos_iou_thr=0.5,
+            neg_iou_thr=0.5,
+            min_pos_iou=0.5,
+            ignore_iof_thr=-1),
+        sampler=dict(
+            type='RandomSampler',
+            num=512,
+            pos_fraction=0.25,
+            neg_pos_ub=-1,
+            add_gt_as_proposals=True),
+        mask_size=28,
+        pos_weight=-1,
+        debug=False))
+test_cfg = dict(
+    rpn=dict(
+        nms_across_levels=False,
+        nms_pre=1000,
+        nms_post=1000,
+        max_num=1000,
+        nms_thr=0.7,
+        min_bbox_size=0),
+    rcnn=dict(
+        score_thr=0.05,
+        nms=dict(type='nms', iou_thr=0.5),
+        max_per_img=100,
+        mask_thr_binary=0.5))
+# dataset settings
+dataset_type = 'CocoDataset'
+data_root = 'data/coco/'
+img_norm_cfg = dict(
+    mean=[123.675, 116.28, 103.53], std=[58.395, 57.12, 57.375], to_rgb=True)
+data = dict(
+    imgs_per_gpu=2,
+    workers_per_gpu=2,
+    train=dict(
+        type=dataset_type,
+        ann_file=data_root + 'annotations/instances_train2017.json',
+        img_prefix=data_root + 'train2017/',
+        img_scale=(1333, 800),
+        img_norm_cfg=img_norm_cfg,
+        size_divisor=32,
+        flip_ratio=0.5,
+        with_mask=True,
+        with_crowd=True,
+        with_label=True),
+    val=dict(
+        type=dataset_type,
+        ann_file=data_root + 'annotations/instances_val2017.json',
+        img_prefix=data_root + 'val2017/',
+        img_scale=(1333, 800),
+        img_norm_cfg=img_norm_cfg,
+        size_divisor=32,
+        flip_ratio=0,
+        with_mask=True,
+        with_crowd=True,
+        with_label=True),
+    test=dict(
+        type=dataset_type,
+        ann_file=data_root + 'annotations/instances_val2017.json',
+        img_prefix=data_root + 'val2017/',
+        img_scale=(1333, 800),
+        img_norm_cfg=img_norm_cfg,
+        size_divisor=32,
+        flip_ratio=0,
+        with_mask=False,
+        with_label=False,
+        test_mode=True))
+# optimizer
+optimizer = dict(type='SGD', lr=0.02, momentum=0.9, weight_decay=0.0001)
+optimizer_config = dict(grad_clip=dict(max_norm=35, norm_type=2))
+# learning policy
+lr_config = dict(
+    policy='step',
+    warmup='linear',
+    warmup_iters=500,
+    warmup_ratio=1.0 / 3,
+    step=[8, 11])
+checkpoint_config = dict(interval=1)
+# yapf:disable
+log_config = dict(
+    interval=50,
+    hooks=[
+        dict(type='TextLoggerHook'),
+        # dict(type='TensorboardLoggerHook')
+    ])
+# yapf:enable
+# runtime settings
+total_epochs = 12
+dist_params = dict(backend='nccl')
+log_level = 'INFO'
+work_dir = './work_dirs/mask_rcnn_r4_gcb_c3-c5_r50_fpn_syncbn_1x'
+load_from = None
+resume_from = None
+workflow = [('train', 1)]

configs/gcnet/mask_rcnn_r50_fpn_sbn_1x.py

+# model settings
+norm_cfg = dict(type='SyncBN', requires_grad=True)
+
+model = dict(
+    type='MaskRCNN',
+    pretrained='modelzoo://resnet50',
+    backbone=dict(
+        type='ResNet',
+        depth=50,
+        num_stages=4,
+        out_indices=(0, 1, 2, 3),
+        frozen_stages=1,
+        style='pytorch',
+        norm_eval=False,
+        norm_cfg=norm_cfg),
+    neck=dict(
+        type='FPN',
+        in_channels=[256, 512, 1024, 2048],
+        out_channels=256,
+        num_outs=5),
+    rpn_head=dict(
+        type='RPNHead',
+        in_channels=256,
+        feat_channels=256,
+        anchor_scales=[8],
+        anchor_ratios=[0.5, 1.0, 2.0],
+        anchor_strides=[4, 8, 16, 32, 64],
+        target_means=[.0, .0, .0, .0],
+        target_stds=[1.0, 1.0, 1.0, 1.0],
+        loss_cls=dict(
+            type='CrossEntropyLoss', use_sigmoid=True, loss_weight=1.0),
+        loss_bbox=dict(type='SmoothL1Loss', beta=1.0 / 9.0, loss_weight=1.0)),
+    bbox_roi_extractor=dict(
+        type='SingleRoIExtractor',
+        roi_layer=dict(type='RoIAlign', out_size=7, sample_num=2),
+        out_channels=256,
+        featmap_strides=[4, 8, 16, 32]),
+    bbox_head=dict(
+        type='SharedFCBBoxHead',
+        num_fcs=2,
+        in_channels=256,
+        fc_out_channels=1024,
+        roi_feat_size=7,
+        num_classes=81,
+        target_means=[0., 0., 0., 0.],
+        target_stds=[0.1, 0.1, 0.2, 0.2],
+        reg_class_agnostic=False,
+        loss_cls=dict(
+            type='CrossEntropyLoss', use_sigmoid=False, loss_weight=1.0),
+        loss_bbox=dict(type='SmoothL1Loss', beta=1.0, loss_weight=1.0)),
+    mask_roi_extractor=dict(
+        type='SingleRoIExtractor',
+        roi_layer=dict(type='RoIAlign', out_size=14, sample_num=2),
+        out_channels=256,
+        featmap_strides=[4, 8, 16, 32]),
+    mask_head=dict(
+        type='FCNMaskHead',
+        num_convs=4,
+        in_channels=256,
+        conv_out_channels=256,
+        num_classes=81,
+        loss_mask=dict(
+            type='CrossEntropyLoss', use_mask=True, loss_weight=1.0)))
+# model training and testing settings
+train_cfg = dict(
+    rpn=dict(
+        assigner=dict(
+            type='MaxIoUAssigner',
+            pos_iou_thr=0.7,
+            neg_iou_thr=0.3,
+            min_pos_iou=0.3,
+            ignore_iof_thr=-1),
+        sampler=dict(
+            type='RandomSampler',
+            num=256,
+            pos_fraction=0.5,
+            neg_pos_ub=-1,
+            add_gt_as_proposals=False),
+        allowed_border=0,
+        pos_weight=-1,
+        debug=False),
+    rpn_proposal=dict(
+        nms_across_levels=False,
+        nms_pre=2000,
+        nms_post=2000,
+        max_num=2000,
+        nms_thr=0.7,
+        min_bbox_size=0),
+    rcnn=dict(
+        assigner=dict(
+            type='MaxIoUAssigner',
+            pos_iou_thr=0.5,
+            neg_iou_thr=0.5,
+            min_pos_iou=0.5,
+            ignore_iof_thr=-1),
+        sampler=dict(
+            type='RandomSampler',
+            num=512,
+            pos_fraction=0.25,
+            neg_pos_ub=-1,
+            add_gt_as_proposals=True),
+        mask_size=28,
+        pos_weight=-1,
+        debug=False))
+test_cfg = dict(
+    rpn=dict(
+        nms_across_levels=False,
+        nms_pre=1000,
+        nms_post=1000,
+        max_num=1000,
+        nms_thr=0.7,
+        min_bbox_size=0),
+    rcnn=dict(
+        score_thr=0.05,
+        nms=dict(type='nms', iou_thr=0.5),
+        max_per_img=100,
+        mask_thr_binary=0.5))
+# dataset settings
+dataset_type = 'CocoDataset'
+data_root = 'data/coco/'
+img_norm_cfg = dict(
+    mean=[123.675, 116.28, 103.53], std=[58.395, 57.12, 57.375], to_rgb=True)
+data = dict(
+    imgs_per_gpu=2,
+    workers_per_gpu=2,
+    train=dict(
+        type=dataset_type,
+        ann_file=data_root + 'annotations/instances_train2017.json',
+        img_prefix=data_root + 'train2017/',
+        img_scale=(1333, 800),
+        img_norm_cfg=img_norm_cfg,
+        size_divisor=32,
+        flip_ratio=0.5,
+        with_mask=True,
+        with_crowd=True,
+        with_label=True),
+    val=dict(
+        type=dataset_type,
+        ann_file=data_root + 'annotations/instances_val2017.json',
+        img_prefix=data_root + 'val2017/',
+        img_scale=(1333, 800),
+        img_norm_cfg=img_norm_cfg,
+        size_divisor=32,
+        flip_ratio=0,
+        with_mask=True,
+        with_crowd=True,
+        with_label=True),
+    test=dict(
+        type=dataset_type,
+        ann_file=data_root + 'annotations/instances_val2017.json',
+        img_prefix=data_root + 'val2017/',
+        img_scale=(1333, 800),
+        img_norm_cfg=img_norm_cfg,
+        size_divisor=32,
+        flip_ratio=0,
+        with_mask=False,
+        with_label=False,
+        test_mode=True))
+# optimizer
+optimizer = dict(type='SGD', lr=0.02, momentum=0.9, weight_decay=0.0001)
+optimizer_config = dict(grad_clip=dict(max_norm=35, norm_type=2))
+# learning policy
+lr_config = dict(
+    policy='step',
+    warmup='linear',
+    warmup_iters=500,
+    warmup_ratio=1.0 / 3,
+    step=[8, 11])
+checkpoint_config = dict(interval=1)
+# yapf:disable
+log_config = dict(
+    interval=50,
+    hooks=[
+        dict(type='TextLoggerHook'),
+        # dict(type='TensorboardLoggerHook')
+    ])
+# yapf:enable
+# runtime settings
+total_epochs = 12
+dist_params = dict(backend='nccl')
+log_level = 'INFO'
+work_dir = './work_dirs/mask_rcnn_r50_fpn_sbn_1x'
+load_from = None
+resume_from = None
+workflow = [('train', 1)]

mmdet/models/backbones/resnet.py

@@ -7,7 +7,7 @@ from torch.nn.modules.batchnorm import _BatchNorm
 from mmcv.cnn import constant_init, kaiming_init
 from mmcv.runner import load_checkpoint
 
-from mmdet.ops import DeformConv, ModulatedDeformConv
+from mmdet.ops import DeformConv, ModulatedDeformConv, ContextBlock
 from ..registry import BACKBONES
 from ..utils import build_conv_layer, build_norm_layer
 
@@ -25,9 +25,11 @@ class BasicBlock(nn.Module):
                  with_cp=False,
                  conv_cfg=None,
                  norm_cfg=dict(type='BN'),
-                 dcn=None):
+                 dcn=None,
+                 gcb=None):
         super(BasicBlock, self).__init__()
         assert dcn is None, "Not implemented yet."
+        assert gcb is None, "Not implemented yet."
 
         self.norm1_name, norm1 = build_norm_layer(norm_cfg, planes, postfix=1)
         self.norm2_name, norm2 = build_norm_layer(norm_cfg, planes, postfix=2)
@@ -92,7 +94,8 @@ class Bottleneck(nn.Module):
                  with_cp=False,
                  conv_cfg=None,
                  norm_cfg=dict(type='BN'),
-                 dcn=None):
+                 dcn=None,
+                 gcb=None):
         """Bottleneck block for ResNet.
         If style is "pytorch", the stride-two layer is the 3x3 conv layer,
         if it is "caffe", the stride-two layer is the first 1x1 conv layer.
@@ -100,6 +103,7 @@ class Bottleneck(nn.Module):
         super(Bottleneck, self).__init__()
         assert style in ['pytorch', 'caffe']
         assert dcn is None or isinstance(dcn, dict)
+        assert gcb is None or isinstance(gcb, dict)
         self.inplanes = inplanes
         self.planes = planes
         self.stride = stride
@@ -110,6 +114,8 @@ class Bottleneck(nn.Module):
         self.norm_cfg = norm_cfg
         self.dcn = dcn
         self.with_dcn = dcn is not None
+        self.gcb = gcb
+        self.with_gcb = gcb is not None
         if self.style == 'pytorch':
             self.conv1_stride = 1
             self.conv2_stride = stride
@@ -181,6 +187,12 @@ class Bottleneck(nn.Module):
 
         self.relu = nn.ReLU(inplace=True)
         self.downsample = downsample
+        if self.with_gcb:
+            gcb_inplanes = planes * self.expansion
+            self.context_block = ContextBlock(
+                inplanes=gcb_inplanes,
+                **gcb
+            )
 
     @property
     def norm1(self):
@@ -219,6 +231,9 @@ class Bottleneck(nn.Module):
             out = self.conv3(out)
             out = self.norm3(out)
 
+            if self.with_gcb:
+                out = self.context_block(out)
+
             if self.downsample is not None:
                 identity = self.downsample(x)
 
@@ -246,7 +261,8 @@ def make_res_layer(block,
                    with_cp=False,
                    conv_cfg=None,
                    norm_cfg=dict(type='BN'),
-                   dcn=None):
+                   dcn=None,
+                   gcb=None):
     downsample = None
     if stride != 1 or inplanes != planes * block.expansion:
         downsample = nn.Sequential(
@@ -272,7 +288,8 @@ def make_res_layer(block,
             with_cp=with_cp,
             conv_cfg=conv_cfg,
             norm_cfg=norm_cfg,
-            dcn=dcn))
+            dcn=dcn,
+            gcb=gcb))
     inplanes = planes * block.expansion
     for i in range(1, blocks):
         layers.append(
@@ -285,7 +302,8 @@ def make_res_layer(block,
                 with_cp=with_cp,
                 conv_cfg=conv_cfg,
                 norm_cfg=norm_cfg,
-                dcn=dcn))
+                dcn=dcn,
+                gcb=gcb))
 
     return nn.Sequential(*layers)
 
@@ -336,6 +354,8 @@ class ResNet(nn.Module):
                  norm_eval=True,
                  dcn=None,
                  stage_with_dcn=(False, False, False, False),
+                 gcb=None,
+                 stage_with_gcb=(False, False, False, False),
                  with_cp=False,
                  zero_init_residual=True):
         super(ResNet, self).__init__()
@@ -359,6 +379,10 @@ class ResNet(nn.Module):
         self.stage_with_dcn = stage_with_dcn
         if dcn is not None:
             assert len(stage_with_dcn) == num_stages
+        self.gcb = gcb
+        self.stage_with_gcb = stage_with_gcb
+        if gcb is not None:
+            assert len(stage_with_gcb) == num_stages
         self.zero_init_residual = zero_init_residual
         self.block, stage_blocks = self.arch_settings[depth]
         self.stage_blocks = stage_blocks[:num_stages]
@@ -371,6 +395,7 @@ class ResNet(nn.Module):
             stride = strides[i]
             dilation = dilations[i]
             dcn = self.dcn if self.stage_with_dcn[i] else None
+            gcb = self.gcb if self.stage_with_gcb[i] else None
             planes = 64 * 2**i
             res_layer = make_res_layer(
                 self.block,
@@ -383,7 +408,8 @@ class ResNet(nn.Module):
                 with_cp=with_cp,
                 conv_cfg=conv_cfg,
                 norm_cfg=norm_cfg,
-                dcn=dcn)
+                dcn=dcn,
+                gcb=gcb)
             self.inplanes = planes * self.block.expansion
             layer_name = 'layer{}'.format(i + 1)
             self.add_module(layer_name, res_layer)

mmdet/models/backbones/resnext.py

@@ -103,7 +103,8 @@ def make_res_layer(block,
                    with_cp=False,
                    conv_cfg=None,
                    norm_cfg=dict(type='BN'),
-                   dcn=None):
+                   dcn=None,
+                   gcb=None):
     downsample = None
     if stride != 1 or inplanes != planes * block.expansion:
         downsample = nn.Sequential(
@@ -131,7 +132,8 @@ def make_res_layer(block,
             with_cp=with_cp,
             conv_cfg=conv_cfg,
             norm_cfg=norm_cfg,
-            dcn=dcn))
+            dcn=dcn,
+            gcb=gcb))
     inplanes = planes * block.expansion
     for i in range(1, blocks):
         layers.append(
@@ -146,7 +148,8 @@ def make_res_layer(block,
                 with_cp=with_cp,
                 conv_cfg=conv_cfg,
                 norm_cfg=norm_cfg,
-                dcn=dcn))
+                dcn=dcn,
+                gcb=gcb))
 
     return nn.Sequential(*layers)
 
@@ -195,6 +198,7 @@ class ResNeXt(ResNet):
             stride = self.strides[i]
             dilation = self.dilations[i]
             dcn = self.dcn if self.stage_with_dcn[i] else None
+            gcb = self.gcb if self.stage_with_gcb[i] else None
             planes = 64 * 2**i
             res_layer = make_res_layer(
                 self.block,
@@ -209,7 +213,8 @@ class ResNeXt(ResNet):
                 with_cp=self.with_cp,
                 conv_cfg=self.conv_cfg,
                 norm_cfg=self.norm_cfg,
-                dcn=dcn)
+                dcn=dcn,
+                gcb=gcb)
             self.inplanes = planes * self.block.expansion
             layer_name = 'layer{}'.format(i + 1)
             self.add_module(layer_name, res_layer)

mmdet/ops/__init__.py

@@ -2,6 +2,7 @@ from .dcn import (DeformConv, DeformConvPack, ModulatedDeformConv,
                   ModulatedDeformConvPack, DeformRoIPooling,
                   DeformRoIPoolingPack, ModulatedDeformRoIPoolingPack,
                   deform_conv, modulated_deform_conv, deform_roi_pooling)
+from .gcb import ContextBlock
 from .nms import nms, soft_nms
 from .roi_align import RoIAlign, roi_align
 from .roi_pool import RoIPool, roi_pool
@@ -14,5 +15,5 @@ __all__ = [
     'ModulatedDeformRoIPoolingPack', 'ModulatedDeformConv',
     'ModulatedDeformConvPack', 'deform_conv', 'modulated_deform_conv',
     'deform_roi_pooling', 'SigmoidFocalLoss', 'sigmoid_focal_loss',
-    'MaskedConv2d'
+    'MaskedConv2d', 'ContextBlock'
 ]

mmdet/ops/gcb/__init__.py

+from .context_block import ContextBlock
+
+__all__ = [
+    'ContextBlock',
+]

mmdet/ops/gcb/context_block.py

+import torch
+from mmcv.cnn import constant_init, kaiming_init
+from torch import nn
+
+
+def last_zero_init(m):
+    if isinstance(m, nn.Sequential):
+        constant_init(m[-1], val=0)
+    else:
+        constant_init(m, val=0)
+
+
+class ContextBlock(nn.Module):
+
+    def __init__(self,
+                 inplanes,
+                 ratio,
+                 pooling_type='att',
+                 fusion_types=('channel_add', )):
+        super(ContextBlock, self).__init__()
+        assert pooling_type in ['avg', 'att']
+        assert isinstance(fusion_types, (list, tuple))
+        valid_fusion_types = ['channel_add', 'channel_mul']
+        assert all([f in valid_fusion_types for f in fusion_types])
+        assert len(fusion_types) > 0, 'at least one fusion should be used'
+        self.inplanes = inplanes
+        self.ratio = ratio
+        self.planes = int(inplanes * ratio)
+        self.pooling_type = pooling_type
+        self.fusion_types = fusion_types
+        if pooling_type == 'att':
+            self.conv_mask = nn.Conv2d(inplanes, 1, kernel_size=1)
+            self.softmax = nn.Softmax(dim=2)
+        else:
+            self.avg_pool = nn.AdaptiveAvgPool2d(1)
+        if 'channel_add' in fusion_types:
+            self.channel_add_conv = nn.Sequential(
+                nn.Conv2d(self.inplanes, self.planes, kernel_size=1),
+                nn.LayerNorm([self.planes, 1, 1]),
+                nn.ReLU(inplace=True),  # yapf: disable
+                nn.Conv2d(self.planes, self.inplanes, kernel_size=1))
+        else:
+            self.channel_add_conv = None
+        if 'channel_mul' in fusion_types:
+            self.channel_mul_conv = nn.Sequential(
+                nn.Conv2d(self.inplanes, self.planes, kernel_size=1),
+                nn.LayerNorm([self.planes, 1, 1]),
+                nn.ReLU(inplace=True),  # yapf: disable
+                nn.Conv2d(self.planes, self.inplanes, kernel_size=1))
+        else:
+            self.channel_mul_conv = None
+        self.reset_parameters()
+
+    def reset_parameters(self):
+        if self.pooling_type == 'att':
+            kaiming_init(self.conv_mask, mode='fan_in')
+            self.conv_mask.inited = True
+
+        if self.channel_add_conv is not None:
+            last_zero_init(self.channel_add_conv)
+        if self.channel_mul_conv is not None:
+            last_zero_init(self.channel_mul_conv)
+
+    def spatial_pool(self, x):
+        batch, channel, height, width = x.size()
+        if self.pooling_type == 'att':
+            input_x = x
+            # [N, C, H * W]
+            input_x = input_x.view(batch, channel, height * width)
+            # [N, 1, C, H * W]
+            input_x = input_x.unsqueeze(1)
+            # [N, 1, H, W]
+            context_mask = self.conv_mask(x)
+            # [N, 1, H * W]
+            context_mask = context_mask.view(batch, 1, height * width)
+            # [N, 1, H * W]
+            context_mask = self.softmax(context_mask)
+            # [N, 1, H * W, 1]
+            context_mask = context_mask.unsqueeze(-1)
+            # [N, 1, C, 1]
+            context = torch.matmul(input_x, context_mask)
+            # [N, C, 1, 1]
+            context = context.view(batch, channel, 1, 1)
+        else:
+            # [N, C, 1, 1]
+            context = self.avg_pool(x)
+
+        return context
+
+    def forward(self, x):
+        # [N, C, 1, 1]
+        context = self.spatial_pool(x)
+
+        out = x
+        if self.channel_mul_conv is not None:
+            # [N, C, 1, 1]
+            channel_mul_term = torch.sigmoid(self.channel_mul_conv(context))
+            out = out * channel_mul_term
+        if self.channel_add_conv is not None:
+            # [N, C, 1, 1]
+            channel_add_term = self.channel_add_conv(context)
+            out = out + channel_add_term
+
+        return out