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authorRoman Gushchin <guro@fb.com>2021-06-29 05:36:03 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-06-29 20:53:48 +0300
commitc22d70a162d3cc177282c4487be4d54876ca55c8 (patch)
tree8ec81fd16974b7d3730edfd50eabcbaf0cac7387 /include
parentf5fbe6b7ad6ef1fbdf8074a6ca9fdab739bf86d4 (diff)
downloadlinux-c22d70a162d3cc177282c4487be4d54876ca55c8.tar.xz
writeback, cgroup: release dying cgwbs by switching attached inodes
Asynchronously try to release dying cgwbs by switching attached inodes to the nearest living ancestor wb. It helps to get rid of per-cgroup writeback structures themselves and of pinned memory and block cgroups, which are significantly larger structures (mostly due to large per-cpu statistics data). This prevents memory waste and helps to avoid different scalability problems caused by large piles of dying cgroups. Reuse the existing mechanism of inode switching used for foreign inode detection. To speed things up batch up to 115 inode switching in a single operation (the maximum number is selected so that the resulting struct inode_switch_wbs_context can fit into 1024 bytes). Because every switching consists of two steps divided by an RCU grace period, it would be too slow without batching. Please note that the whole batch counts as a single operation (when increasing/decreasing isw_nr_in_flight). This allows to keep umounting working (flush the switching queue), however prevents cleanups from consuming the whole switching quota and effectively blocking the frn switching. A cgwb cleanup operation can fail due to different reasons (e.g. not enough memory, the cgwb has an in-flight/pending io, an attached inode in a wrong state, etc). In this case the next scheduled cleanup will make a new attempt. An attempt is made each time a new cgwb is offlined (in other words a memcg and/or a blkcg is deleted by a user). In the future an additional attempt scheduled by a timer can be implemented. [guro@fb.com: replace open-coded "115" with arithmetic] Link: https://lkml.kernel.org/r/YMEcSBcq/VXMiPPO@carbon.dhcp.thefacebook.com [guro@fb.com: add smp_mb() to inode_prepare_wbs_switch()] Link: https://lkml.kernel.org/r/YMFa+guFw7OFjf3X@carbon.dhcp.thefacebook.com [willy@infradead.org: fix documentation] Link: https://lkml.kernel.org/r/20210615200242.1716568-2-willy@infradead.org Link: https://lkml.kernel.org/r/20210608230225.2078447-9-guro@fb.com Signed-off-by: Roman Gushchin <guro@fb.com> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Acked-by: Tejun Heo <tj@kernel.org> Acked-by: Dennis Zhou <dennis@kernel.org> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Dave Chinner <dchinner@redhat.com> Cc: Jan Kara <jack@suse.com> Cc: Jens Axboe <axboe@kernel.dk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/backing-dev-defs.h1
-rw-r--r--include/linux/writeback.h1
2 files changed, 2 insertions, 0 deletions
diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index 63f52ad2ce7a..1d7edad9914f 100644
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -155,6 +155,7 @@ struct bdi_writeback {
struct list_head memcg_node; /* anchored at memcg->cgwb_list */
struct list_head blkcg_node; /* anchored at blkcg->cgwb_list */
struct list_head b_attached; /* attached inodes, protected by list_lock */
+ struct list_head offline_node; /* anchored at offline_cgwbs */
union {
struct work_struct release_work;
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 8e5c5bb16e2d..95de51c10248 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -221,6 +221,7 @@ void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr_pages,
enum wb_reason reason, struct wb_completion *done);
void cgroup_writeback_umount(void);
+bool cleanup_offline_cgwb(struct bdi_writeback *wb);
/**
* inode_attach_wb - associate an inode with its wb