linux-kernel - Re: [PATCH v4] memcg: charge before adding to swapcache on swapin

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CALvZod5oPTj8r6vKXVGgtKoXVaRWbRX9S2mLVtSnyysqtzr_ng@mail.gmail.com>
Date:   Fri, 5 Mar 2021 13:53:54 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Hugh Dickins <hughd@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>
Cc:     Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Cgroups <cgroups@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] memcg: charge before adding to swapcache on swapin

On Fri, Mar 5, 2021 at 1:26 PM Shakeel Butt <shakeelb@...gle.com> wrote:
>
> Currently the kernel adds the page, allocated for swapin, to the
> swapcache before charging the page. This is fine but now we want a
> per-memcg swapcache stat which is essential for folks who wants to
> transparently migrate from cgroup v1's memsw to cgroup v2's memory and
> swap counters. In addition charging a page before exposing it to other
> parts of the kernel is a step in the right direction.
>
> To correctly maintain the per-memcg swapcache stat, this patch has
> adopted to charge the page before adding it to swapcache. One
> challenge in this option is the failure case of add_to_swap_cache() on
> which we need to undo the mem_cgroup_charge(). Specifically undoing
> mem_cgroup_uncharge_swap() is not simple.
>
> To resolve the issue, this patch introduces transaction like interface
> to charge a page for swapin. The function mem_cgroup_charge_swapin_page()
> initiates the charging of the page and mem_cgroup_finish_swapin_page()
> completes the charging process. So, the kernel starts the charging
> process of the page for swapin with mem_cgroup_charge_swapin_page(),
> adds the page to the swapcache and on success completes the charging
> process with mem_cgroup_finish_swapin_page().

And of course I forgot to update the commit message.

Andrew, please replace the third paragraph with the following para:

To resolve the issue, this patch decouples the charging for swapin pages from
mem_cgroup_charge(). Two new functions are introduced,
mem_cgroup_swapin_charge_page() for just charging the swapin page and
mem_cgroup_swapin_uncharge_swap() for uncharging the swap slot once the
page has been successfully added to the swapcache.