Messages in this thread | | | Subject | Re: [PATCH 2/2] drm/ttm: optimize the pool shrinker a bit v2 | From | Christian König <> | Date | Fri, 16 Apr 2021 09:08:51 +0200 |
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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.
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