lkml.org 
[lkml]   [2021]   [Apr]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 2/2] drm/ttm: optimize the pool shrinker a bit v2
From
Date
Am 15.04.21 um 22:33 schrieb Andrew Morton:
> On Thu, 15 Apr 2021 13:56:24 +0200 "Christian König" <ckoenig.leichtzumerken@gmail.com> wrote:
>
>> @@ -530,6 +525,11 @@ void ttm_pool_fini(struct ttm_pool *pool)
>> for (j = 0; j < MAX_ORDER; ++j)
>> ttm_pool_type_fini(&pool->caching[i].orders[j]);
>> }
>> +
>> + /* We removed the pool types from the LRU, but we need to also make sure
>> + * that no shrinker is concurrently freeing pages from the pool.
>> + */
>> + sync_shrinkers();
> It isn't immediately clear to me how this works. ttm_pool_fini() has
> already freed all the pages hasn't it? So why would it care if some
> shrinkers are still playing with the pages?

Yes ttm_pool_fini() has freed up all pages which had been in the pool
when the function was called.

But the problem is it is possible that a parallel running shrinker has
taken a page from the pool and is in the process of freeing it up.

When I return here the pool structure and especially the device
structure are freed while the parallel running shrinker is still using them.

I could go for a design where we have one shrinker per device instead,
but that would put a bit to much pressure on the pool in my opinion.

> Or is it the case that ttm_pool_fini() is assuming that there will be
> some further action against these pages, which requires that shrinkers
> no longer be accessing the pages and which further assumes that future
> shrinker invocations will not be able to look up these pages?
>
> IOW, a bit more explanation about the dynamics here would help!

Sorry, I'm not a native speaker of English and sometimes still have a
hard time explaining things.

Regards,
Christian.

\
 
 \ /
  Last update: 2021-04-16 09:10    [W:0.500 / U:0.196 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site