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From:   Alexander Shishkin <alexander.shishkin@linux.intel.com>
To:     Song Liu <songliubraving@fb.com>
Cc:     linux-kernel <linux-kernel@vger.kernel.org>,
        Kernel Team <Kernel-team@fb.com>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        alexander.shishkin@linux.intel.com
Subject: Re: [PATCH] perf/core: fix mlock accounting in perf_mmap()
In-Reply-To: <79CAEE07-57BC-4915-A812-DD99AAF1B809@fb.com>
References: <20200117234503.1324050-1-songliubraving@fb.com> <87blqybknz.fsf@ashishki-desk.ger.corp.intel.com> <79CAEE07-57BC-4915-A812-DD99AAF1B809@fb.com>
Date:   Thu, 23 Jan 2020 11:19:44 +0200
Message-ID: <875zh2bkcv.fsf@ashishki-desk.ger.corp.intel.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Song Liu <songliubraving@fb.com> writes:

>> On Jan 20, 2020, at 12:24 AM, Alexander Shishkin <alexander.shishkin@linux.intel.com> wrote:
>> 
>> Song Liu <songliubraving@fb.com> writes:
>> 
>>> sysctl_perf_event_mlock and user->locked_vm can change value
>>> independently, so we can't guarantee:
>>> 
>>>    user->locked_vm <= user_lock_limit
>> 
>> This means: if the sysctl got sufficiently decreased, so that the
>> existing locked_vm exceeds it, we need to deal with the overflow, right?
>
> Reducing sysctl is one way to generate the overflow. Another way is to 
> call setrlimit() from user space to allow bigger user->locked_vm. 

You mean RLIMIT_MEMLOCK? That's a limit on mm->pinned_vm. Doesn't affect
user->locked_vm.

Regards,
--
Alex