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From:   Yosry Ahmed <yosryahmed@google.com>
Date:   Thu, 7 Apr 2022 22:00:07 -0700
Message-ID: <CAJD7tkZNAts_4M9TZx02L1y24hp5ty4H5vgrzryZk4a_uFR=6Q@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>,
        =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>,
        Tim Chen <tim.c.chen@linux.intel.com>, cgroups@vger.kernel.org,
        linux-doc@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>, linux-kselftest@vger.kernel.org,
        Michal Hocko <mhocko@kernel.org>,
        Shakeel Butt <shakeelb@google.com>,
        Roman Gushchin <roman.gushchin@linux.dev>
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On Thu, Apr 7, 2022 at 4:04 PM Yosry Ahmed <yosryahmed@google.com> wrote:
>
> 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)?

Never mind I already sent v3 and removed it with other fixes.
>
> Thanks!
>
> > +       free(buf);
> >         return 0;
> >  }
> >
> > --
> > 2.35.1.1178.g4f1659d476-goog
> >