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From:   Wolfgang Walter <linux@stwm.de>
To:     Sasha Levin <sashal@kernel.org>
Cc:     Rik van Riel <riel@surriel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Dave Chinner <dchinner@redhat.com>,
        Roman Gushchin <guro@fb.com>, Spock <dairinin@gmail.com>,
        Michal Hocko <mhocko@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 4.20 71/92] Revert "mm: slowly shrink slabs with a relatively small number of objects"
Date:   Tue, 19 Feb 2019 19:43:22 +0100
Message-ID: <4113759.4IQ3NfHFaI@stwm.de>
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Am Montag, 18. Februar 2019, 14:34:52 schrieb Sasha Levin:
> On Mon, Feb 18, 2019 at 10:30:44AM -0500, Rik van Riel wrote:
> >On Mon, 2019-02-18 at 14:43 +0100, Greg Kroah-Hartman wrote:
> >> 4.20-stable review patch.  If anyone has any objections, please le=
t
> >> me know.
> >>=20
> >> ------------------
> >>=20
> >> From: Dave Chinner <dchinner@redhat.com>
> >>=20
> >> commit a9a238e83fbb0df31c3b9b67003f8f9d1d1b6c96 upstream.
> >>=20
> >> This reverts commit 172b06c32b9497 ("mm: slowly shrink slabs with =
a
> >> relatively small number of objects").
> >
> >This revert will result in the slab caches of dead
> >cgroups with a small number of remaining objects never
> >getting reclaimed, which can be a memory leak in some
> >configurations.
>=20
> What's the "right" choice though? we get either leaky cgroups or hang=
ing
> xfs.

This not only made xfs hang. (Since 4.19.3) on two of our servers ext4 =
got so=20
sluggish that login with ssh needed a minute and more. bash tab complet=
ion was=20
unusable. Sometimes systemd-journald was restarted with "Watchdog timeo=
ut=20
(limit 3min)!", (journal also was on ext4).

>=20
> >But hey, that's your tradeoff to make.
>=20
> I don't think that any decision was made here, the stable tree simply=

> follows upstream with regards to fixes and bugs such as these: we rem=
ain
> "bug compatible" with upstream in these scenarios, there was no decis=
ion
> made to prefer either bug.
>=20
> --
> Thanks,
> Sasha

Regards
--=20
Wolfgang Walter
Studentenwerk M=FCnchen
Anstalt des =F6ffentlichen Rechts