ACK: [PATCH 0/4 v3][bionic:linux] nr_writeback memory leak in kernel 4.15.0-137+

[Thadeu Lima de Souza Cascardo]

On Thu, Apr 29, 2021 at 12:54:53PM -0600, Tim Gardner wrote:
> v2: Added some more fix patches at the suggestion of Thadeu Lima de Souza
> Cascardo <cascardo at canonical.com>
> v3: Proper subject line
> 
> BugLink: https://bugs.launchpad.net/bugs/1926081
> 
> [Impact]
> 
> Ubuntu 18.04.5 4.15.0 LTS kernels at version 4.15.0-137 and above contain a
> memory leak due to the inclusion of patch from the upstream kernel, but not
> the fix for that patch which was released later.
> 
> Bad patch in bionic:linux 2c17fa778db85644458b52a7df8eacc402cbc1ef mm:
> memcontrol: fix excessive complexity in memory.stat reporting
> 
> [Test Plan]
> 
> See bug report for extended discussion. Test results are positive.
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1926081/comments/24
> 
> The following is enough to permanently increase the value of `nr_writeback`.
> 
> cat > breakme.sh <<EOF
> date
> grep nr_writeback /proc/vmstat
> mkdir -p /docker/testfiles/{1..5}
> 
> seq -w 1 100000 | xargs -n1 -I% sh -c 'dd if=/dev/urandom of=/docker/testfiles/1/file.% bs=4k count=10 status=none' &
> seq -w 1 100000 | xargs -n1 -I% sh -c 'dd if=/dev/urandom of=/docker/testfiles/2/file.% bs=4k count=10 status=none' &
> seq -w 1 100000 | xargs -n1 -I% sh -c 'dd if=/dev/urandom of=/docker/testfiles/3/file.% bs=4k count=10 status=none' &
> seq -w 1 100000 | xargs -n1 -I% sh -c 'dd if=/dev/urandom of=/docker/testfiles/4/file.% bs=4k count=10 status=none' &
> seq -w 1 100000 | xargs -n1 -I% sh -c 'dd if=/dev/urandom of=/docker/testfiles/5/file.% bs=4k count=10 status=none' &
> 
> wait $(jobs -p)
> grep nr_writeback /proc/vmstat
> date
> EOF
> 
> [Where problems could occur]
> 
> Memory leakage could continue. The new spinlocks could cause some performance degradation.
> 
> [Other Info]
> 
> All of these patches have been accepted to v4.14.y

3 clean cherry-picks. Backport looks fine too. No followups missing. Nice test
case.

Acked-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>