From 6631142229005e1b1c311a09efe9fb3cfdac8559 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Thu, 13 Jun 2019 15:30:41 -0700
Subject: [PATCH] blkcg, writeback: dead memcgs shouldn't contribute to
writeback ownership arbitration
Git-commit: 6631142229005e1b1c311a09efe9fb3cfdac8559
Patch-mainline: v5.3-rc1
References: bsc#1213022
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>
Acked-by: Jan Kara <jack@suse.cz>
---
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;
--
2.35.3