linux-kernel - Re: [PATCH] perf: rework memory accounting in perf

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Message-ID: <B97C6326-7CA2-4F57-A259-F5FB152E14D1@fb.com>
Date:   Mon, 7 Oct 2019 16:31:37 +0000
From:   Song Liu <songliubraving@...com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     open list <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>, Jie Meng <jmeng@...com>,
        Hechao Li <hechaol@...com>
Subject: Re: [PATCH] perf: rework memory accounting in perf_mmap()

Hi Peter,

> On Sep 30, 2019, at 2:02 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Wed, Sep 04, 2019 at 02:46:18PM -0700, Song Liu wrote:
>> perf_mmap() always increases user->locked_vm. As a result, "extra" could
>> grow bigger than "user_extra", which doesn't make sense. Here is an
>> example case:
>> 
>> Note: Assume "user_lock_limit" is very small.
>> | # of perf_mmap calls |vma->vm_mm->pinned_vm|user->locked_vm|
>> | 0                    | 0                   | 0             |
>> | 1                    | user_extra          | user_extra    |
>> | 2                    | 3 * user_extra      | 2 * user_extra|
>> | 3                    | 6 * user_extra      | 3 * user_extra|
>> | 4                    | 10 * user_extra     | 4 * user_extra|
>> 
>> Fix this by maintaining proper user_extra and extra.
> 
> Aah, indeed.

Thanks for the feedback!

> 
> Also, this code is unreadable (which is mostly my own fault I suppose)
> :/

How does this patch look to you? Is it ready to merge?

Thanks,
Song