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From:   Shakeel Butt <shakeelb@google.com>
Date:   Tue, 27 Jul 2021 14:39:23 -0700
Message-ID: <CALvZod7e8pNhCU-o8-dFwn5v4aVoUrxxjGamfbaqK83d3UL1Mw@mail.gmail.com>
Subject: Re: [PATCH v7 02/10] memcg: enable accounting for pollfd and select
 bits arrays
To:     Vasily Averin <vvs@virtuozzo.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Cgroups <cgroups@vger.kernel.org>,
        Michal Hocko <mhocko@kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Roman Gushchin <guro@fb.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Mon, Jul 26, 2021 at 10:33 PM Vasily Averin <vvs@virtuozzo.com> wrote:
>
> User can call select/poll system calls with a large number of assigned
> file descriptors and force kernel to allocate up to several pages of memory
> till end of these sleeping system calls. We have here long-living
> unaccounted per-task allocations.
>
> It makes sense to account for these allocations to restrict the host's
> memory consumption from inside the memcg-limited container.
>
> Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
> ---
>  fs/select.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/select.c b/fs/select.c
> index 945896d..e83e563 100644
> --- a/fs/select.c
> +++ b/fs/select.c
> @@ -655,7 +655,7 @@ int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
>                         goto out_nofds;
>
>                 alloc_size = 6 * size;
> -               bits = kvmalloc(alloc_size, GFP_KERNEL);
> +               bits = kvmalloc(alloc_size, GFP_KERNEL_ACCOUNT);

What about the similar allocation in compat_core_sys_select()? Also
what about the allocation in poll_get_entry()?

>                 if (!bits)
>                         goto out_nofds;
>         }
> @@ -1000,7 +1000,7 @@ static int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds,
>
>                 len = min(todo, POLLFD_PER_PAGE);
>                 walk = walk->next = kmalloc(struct_size(walk, entries, len),
> -                                           GFP_KERNEL);
> +                                           GFP_KERNEL_ACCOUNT);
>                 if (!walk) {
>                         err = -ENOMEM;
>                         goto out_fds;
> --
> 1.8.3.1
>