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From:   Yosry Ahmed <yosryahmed@google.com>
Date:   Thu, 7 Apr 2022 16:04:22 -0700
Message-ID: <CAJD7tkaPaXQ4M_w-YxJizD2DG8co-3Q2bVDfd7_FaG2ivgT6UA@mail.gmail.com>
Subject: Re: [PATCH v2 3/4] selftests: cgroup: fix alloc_anon_noexit()
 instantly freeing memory
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     David Rientjes <rientjes@google.com>, Tejun Heo <tj@kernel.org>,
        Zefan Li <lizefan.x@bytedance.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Shuah Khan <shuah@kernel.org>, Yu Zhao <yuzhao@google.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Wei Xu <weixugc@google.com>, Greg Thelen <gthelen@google.com>,
        Chen Wandun <chenwandun@huawei.com>,
        Vaibhav Jain <vaibhav@linux.ibm.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Huang@google.com,
        Ying <ying.huang@intel.com>,
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On Thu, Apr 7, 2022 at 3:43 PM Yosry Ahmed <yosryahmed@google.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@google.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
>