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SubjectRe: [PATCH 5/5] blkcg, writeback: dead memcgs shouldn't contribute to writeback ownership arbitration
On Thu 13-06-19 15:30:41, Tejun Heo wrote:
> 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>

I see Jens has already pulled the changes so this is mostly informative but
the patch looks good to me.

Honza
> ---
> fs/fs-writeback.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index e41cbe8e81b9..9ebfb1b28430 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -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;
> --
> 2.17.1
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR

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