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authorTejun Heo <tj@kernel.org>2019-11-08 23:18:29 +0300
committerJens Axboe <axboe@kernel.dk>2019-11-08 23:37:24 +0300
commit65de03e251382306a4575b1779c57c87889eee49 (patch)
treeab8166a34aa1f1b32acefb5b7ea09ce0442eb7d4
parent8e9c523016cf9983b295e4bc659183d1fa6ef8e0 (diff)
downloadlinux-65de03e251382306a4575b1779c57c87889eee49.tar.xz
cgroup,writeback: don't switch wbs immediately on dead wbs if the memcg is dead
cgroup writeback tries to refresh the associated wb immediately if the current wb is dead. This is to avoid keeping issuing IOs on the stale wb after memcg - blkcg association has changed (ie. when blkcg got disabled / enabled higher up in the hierarchy). Unfortunately, the logic gets triggered spuriously on inodes which are associated with dead cgroups. When the logic is triggered on dead cgroups, the attempt fails only after doing quite a bit of work allocating and initializing a new wb. While c3aab9a0bd91 ("mm/filemap.c: don't initiate writeback if mapping has no dirty pages") alleviated the issue significantly as it now only triggers when the inode has dirty pages. However, the condition can still be triggered before the inode is switched to a different cgroup and the logic simply doesn't make sense. Skip the immediate switching if the associated memcg is dying. This is a simplified version of the following two patches: * https://lore.kernel.org/linux-mm/20190513183053.GA73423@dennisz-mbp/ * http://lkml.kernel.org/r/156355839560.2063.5265687291430814589.stgit@buzz Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Fixes: e8a7abf5a5bd ("writeback: disassociate inodes from dying bdi_writebacks") Acked-by: Dennis Zhou <dennis@kernel.org> Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--fs/fs-writeback.c9
1 files changed, 6 insertions, 3 deletions
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 8461a6322039..335607b8c5c0 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -576,10 +576,13 @@ void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
spin_unlock(&inode->i_lock);
/*
- * A dying wb indicates that the memcg-blkcg mapping has changed
- * and a new wb is already serving the memcg. Switch immediately.
+ * A dying wb indicates that either the blkcg associated with the
+ * memcg changed or the associated memcg is dying. In the first
+ * case, a replacement wb should already be available and we should
+ * refresh the wb immediately. In the second case, trying to
+ * refresh will keep failing.
*/
- if (unlikely(wb_dying(wbc->wb)))
+ if (unlikely(wb_dying(wbc->wb) && !css_is_dying(wbc->wb->memcg_css)))
inode_switch_wbs(inode, wbc->wb_id);
}
EXPORT_SYMBOL_GPL(wbc_attach_and_unlock_inode);