Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Mon, 28 Jun 2021 15:30:40 +0200
From:   Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>
To:     "Enrico Weigelt, metux IT consult" <lkml@metux.net>
Cc:     Philipp Hahn <pmhahn+lkml@pmhahn.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "cgroups@vger.kernel.org" <cgroups@vger.kernel.org>
Subject: Re: Prevent inode/dentry trashing?
Message-ID: <YNnPAJ4HNoN6g6T9@blackbook>
References: <ce330972-78e6-4347-9735-72ee7bb21ef5@pmhahn.de>
 <YNX8anv2yCnkVPXy@blackbook>
 <88451906-e537-0ac3-b8f2-16bfc4d77ea6@metux.net>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha256;
        protocol="application/pgp-signature"; boundary="23tDw59TYEHMEItr"
Content-Disposition: inline
In-Reply-To: <88451906-e537-0ac3-b8f2-16bfc4d77ea6@metux.net>
Precedence: bulk


--23tDw59TYEHMEItr
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline

On Mon, Jun 28, 2021 at 11:40:39AM +0200, "Enrico Weigelt, metux IT consult" <lkml@metux.net> wrote:
> Could you please tell a bit more how this really works ?
> (maybe some pointers to the code)

When cgroup's consumption is about to cross the configured limit,
reclaim is started
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/memcontrol.c?id=62fb9874f5da54fdb243003b386128037319b219#n2579

that may evict old entries
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/vmscan.c?id=62fb9874f5da54fdb243003b386128037319b219#n2852

and if there's still no success freeing some space the dentry allocation
can fail
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/slab.h?id=62fb9874f5da54fdb243003b386128037319b219#n277

(This describes just one code path, the subject isn't always a dentry.)

> I'm curios what happens if those cache objects are used by different
> cgroups - are they accounted to multiple times (once per cgroup) ?
> What happens when one cgroup using some cache object reaching its limit,
> wile another one does not ?

That's explained here
https://www.kernel.org/doc/html/v5.13/admin-guide/cgroup-v2.html#memory-ownership

Michal

--23tDw59TYEHMEItr
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: Digital signature

-----BEGIN PGP SIGNATURE-----
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=5TgM
-----END PGP SIGNATURE-----

--23tDw59TYEHMEItr--