Commit 66311422 authored Jun 13, 2019 by Tejun Heo Committed by Jens Axboe Jun 15, 2019

blkcg, writeback: dead memcgs shouldn't contribute to writeback ownership arbitration



wbc_account_io() collects information on cgroup ownership of writeback
pages to determine which cgroup should own the inode.  Pages can stay
associated with dead memcgs but we want to avoid attributing IOs to
dead blkcgs as much as possible as the association is likely to be
stale.  However, currently, pages associated with dead memcgs
contribute to the accounting delaying and/or confusing the
arbitration.

Fix it by ignoring pages associated with dead memcgs.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 71c81407

fs/fs-writeback.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -715,6 +715,7 @@ void wbc_detach_inode(struct writeback_control *wbc)
		void wbc_account_io(struct writeback_control wbc, struct page page,
		size_t bytes)
		{
		struct cgroup_subsys_state *css;
		int id;

		/*
		@@ -726,7 +727,12 @@ void wbc_account_io(struct writeback_control wbc, struct page page,
		if (!wbc->wb)
		return;

		id = mem_cgroup_css_from_page(page)->id;
		css = mem_cgroup_css_from_page(page);
		/* dead cgroups shouldn't contribute to inode ownership arbitration */
		if (!(css->flags & CSS_ONLINE))
		return;

		id = css->id;

		if (id == wbc->wb_id) {
		wbc->wb_bytes += bytes;

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