Re: [PATCH] perf: rework memory accounting in perf_mmap()

[Hechao Li]

Song Liu <songliubraving@xxxxxx> wrote on Mon [2019-Sep-16 12:43:16 -0700]:
> Hi Peter,
> 
> > On Sep 4, 2019, at 2:46 PM, Song Liu <songliubraving@xxxxxx> 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.
> > 
> > Reported-by: Hechao Li <hechaol@xxxxxx>
> > Cc: Jie Meng <jmeng@xxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Signed-off-by: Song Liu <songliubraving@xxxxxx>
> 
> Could you please share your feedbacks/comments on this one?
> 
> Thanks,
> Song

The change looks good to me. Thanks, Song.

Reviewed-By: Hechao Li <hechaol@xxxxxx>

Hechao