linux-kernel - Re: [PATCH v2 3/4] selftests: cgroup: fix alloc_anon

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Date:   Thu, 7 Apr 2022 16:04:22 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     David Rientjes <rientjes@...gle.com>, Tejun Heo <tj@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <shuah@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Wei Xu <weixugc@...gle.com>, Greg Thelen <gthelen@...gle.com>,
        Chen Wandun <chenwandun@...wei.com>,
        Vaibhav Jain <vaibhav@...ux.ibm.com>,
        Johannes Weiner <hannes@...xchg.org>, Huang@...gle.com,
        Ying <ying.huang@...el.com>,
        Michal Koutný <mkoutny@...e.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>, cgroups@...r.kernel.org,
        linux-doc@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, linux-kselftest@...r.kernel.org,
        Michal Hocko <mhocko@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>
Subject: Re: [PATCH v2 3/4] selftests: cgroup: fix alloc_anon_noexit()
 instantly freeing memory

On Thu, Apr 7, 2022 at 3:43 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> Currently, alloc_anon_noexit() calls alloc_anon() which instantly frees
> the allocated memory. alloc_anon_noexit() is usually used with
> cg_run_nowait() to run a process in the background that allocates
> memory. It makes sense for the background process to keep the memory
> allocated and not instantly free it (otherwise there is no point of
> running it in the background).
>
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
> ---
>  tools/testing/selftests/cgroup/test_memcontrol.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
> index 36ccf2322e21..c1ec71d83af7 100644
> --- a/tools/testing/selftests/cgroup/test_memcontrol.c
> +++ b/tools/testing/selftests/cgroup/test_memcontrol.c
> @@ -211,13 +211,18 @@ static int alloc_pagecache_50M_noexit(const char *cgroup, void *arg)
>  static int alloc_anon_noexit(const char *cgroup, void *arg)
>  {
>         int ppid = getppid();
> +       size_t size = (unsigned long)arg;
> +       char *buf, *ptr;
>
> -       if (alloc_anon(cgroup, arg))
> -               return -1;
> +       buf = malloc(size);
> +       for (ptr = buf; ptr < buf + size; ptr += PAGE_SIZE)
> +               *ptr = 0;
>
>         while (getppid() == ppid)
>                 sleep(1);
>
> +       printf("Freeing buffer");

Hey Andew,

I am very sorry but I left a debugging printf there by mistake. If
it's no hassle, do you mind removing it from the patch (assuming I
won't need to send a v3 anyway)?

Thanks!

> +       free(buf);
>         return 0;
>  }
>
> --
> 2.35.1.1178.g4f1659d476-goog
>