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

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Message-ID: <20191007165618.GJ4643@worktop.programming.kicks-ass.net>
Date:   Mon, 7 Oct 2019 18:56:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Song Liu <songliubraving@...com>
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()

On Mon, Oct 07, 2019 at 04:31:37PM +0000, Song Liu wrote:
> 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?

Yes, I queued it, I'll get it into tip soon. It got held up due to me
working on some other patches, sorry about that.