Re: [PATCH v3 00/21] TTM shrinker helpers and xe buffer object shrinker

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

Hi, all

On Tue, 2024-05-21 at 09:16 +0200, Thomas Hellström wrote:
> This series implements TTM shrinker / eviction helpers and an xe bo
> shrinker. It builds on two previous series, *and obsoletes these*.
> First
> 
> https://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg484425.html
> 
> Second the previous TTM shrinker series
> 
> https://lore.kernel.org/linux-mm/b7491378-defd-4f1c-31e2-29e4c77e2d67@amd.com/T/
> 
> Where the comment about layering
> https://lore.kernel.org/linux-mm/b7491378-defd-4f1c-31e2-29e4c77e2d67@amd.com/T/#ma918844aa8a6efe8768fdcda0c6590d5c93850c9
> 
> now addressed, and this version also implements shmem objects for
> backup
> rather than direct swap-cache insertions, which was used in the
> previuos
> series. It turns out that with per-page backup / shrinking, shmem
> objects
> appears to work just as well as direct swap-cache insertions with the
> added benefit that was introduced in the previous TTM shrinker series
> to
> avoid running out of swap entries isn't really needed.
> 
> Patch 1-4 implements restartable LRU list iteration.
> 
> Patch 5 implements a LRU walker + resv locking helper
> 
> Patch 6 moves TTM swapping over to the walker.
> 
> Patch 7 moves TTM eviction over to the walker.
> 
> Patch 8 could in theory be skipped but introduces a possibility to
> easily
> add or test multiple backup backends, like the direct swap-cache
> insertion or even files into fast dedicated nvme storage for for
> example.
> 
> Patch 9 introduces helpers in the ttm_pool code for page-by-page
> shrinking
> and recovery. It avoids having to temporarily allocate a huge amount
> of
> memory to be able to shrink a buffer object. It also introduces the
> possibility to immediately write-back pages if needed, since that
> tends
> to be a bit delayed when left to kswapd.
> 
> Patch 10 Adds a simple error injection to the above code to help
> increase
> test coverage.
> 
> Patch 11 Implements an xe bo shrinker and a common helper in TTM for
> shrinking.
> 
> Patch 12-21 are really a separate POC series, for introducing
> drm_exec locking
> in TTM. The patch touches both drm_exec and dma-buf and is for now
> marked as
> an RFC:
> 
> Patch 12 Introduces dma_resv_trylock_ctx.
> 
> Patches 13-14 deal with introducing drm_exec_trylock.
> 
> Patch 15 adds a snapshot capability to drm_exec.
> 
> Patch 16 adds an evict mode locking capability to drm_exec
> 
> Patch 17 converts the LRU + locking walker to drm_exec.
> 
> Patch 18 converts TTM vm to use drm_exec.
> 
> Patch 19 converts the xe fault handler to drm_exec.
> 
> Patch 20 converts bo initialization locking to drm_exec
> 
> Patch 21 introduces drm_exec locking around some of the
> bo validation callsites in drm_exec.
> 
> v2:
> - Squash obsolete revision history in the patch commit messages.
> - Fix a couple of review comments by Christian
> - Don't store the mem_type in the TTM managers but in the
>   resource cursor.
> - Rename introduced TTM *back_up* function names to *backup*
> - Add ttm pool recovery fault injection.
> - Shrinker xe kunit test
> - Various bugfixes
> 
> v3:
> - Address some review comments from Matthew Brost and Christian
> König.
> - Use the restartable LRU walk for TTM swapping and eviction.
> - Provide a POC drm_exec locking implementation for exhaustive
>   eviction. (Christian König).
> 
> Cc: Somalapuram Amaranath <Amaranath.Somalapuram@amd.com>
> Cc: Christian König <christian.koenig@amd.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: <dri-devel@lists.freedesktop.org>

Now with a POC available how the drm_exec locking could be done in TTM
(the RFC part) I think the best approach is to get patch 1-11 reviewed
and pushed, and we could then settle on a solution for the drm_exec
part as a follow-up. Undoubtedly there are a couple of things that need
discussion there, in particular the resv_set, the snapshot and the
trylock memory allocation.

/Thomas