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

[Song Liu]

Hi Peter,

> On Sep 30, 2019, at 2:02 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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