linux-ext4 - [PATCH 0/1] Fix for recent bugzilla reports related to long halts during block allocation

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Message-Id: <cover.1702455010.git.ojaswin@linux.ibm.com>
Date: Fri, 15 Dec 2023 16:49:49 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>
Cc: Ritesh Harjani <ritesh.list@...il.com>, linux-kernel@...r.kernel.org,
        Jan Kara <jack@...e.cz>, glandvador@...oo.com, bugzilla@...l.emu.id.au
Subject: [PATCH 0/1] Fix for recent bugzilla reports related to long halts during block allocation

This patch intends to fix the recent bugzilla [1] report where the
kworker flush thread seemed to be taking 100% CPU utilizationa and was
slowing down the whole system. The backtrace indicated that we were
stuck in mballoc allocation path. The issue was only seen kernel 6.5+
and when ext4 was mounted with -o stripe (or stripe option was
implicitly added due us mkfs flags used).

Although I was not able to fully replicate this issue, from the perf
probe logs collected I have a possible root cause which I have explained
in the patch commit message. 

Now, the one thing I'm still skeptical about is why this was only seen
in kernel 6.5+. We added a new mballoc criteria in kernel 6.5 but I was
not able to find a satisfactory explanation as to why that would have
any effect here. Furter, the issue still persisted when I asked one of
the reporters to disable the it using sysfs file and rerun the test.
Maybe there are some more factors at play? 

Anyways, I would appreciate if the people experiencing this issue can
help test this patch and see if it fixes the regression.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=217965

Regards,
ojaswin

Ojaswin Mujoo (1):
  ext4: fallback to complex scan if aligned scan doesn't work

 fs/ext4/mballoc.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

-- 
2.39.3