Re: [PATCH v2 0/9] TTM shrinker helpers and xe buffer object shrinker

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

Hi, Christian,

On Tue, 2024-04-16 at 13:55 +0200, Christian König wrote:
> While patches 1-4 look good from a high level I still think it needs 
> some prerequisite and re-ordering.
> 
> First of all make all the cleanups separate patches. In other words
> that 
> ttm_resource_manager_next() takes only the cursor as argument, adding
> ttm_resource_cursor_fini()/ttm_resource_cursor_fini_locked() as one 
> patch and then ttm_lru_bulk_move_init()/ttm_lru_bulk_move_fini() as
> second.

Yes, I can take a look at that. I think the shortening of the argument
list of ttm_resource_manager_next() makes sense as a separate cleanup. 

The other two are needed because of the changes introduced in the
respective patches. I could of course add stubs of these functions
before the patch that currently introduce them if needed, but don't
really see the point. What do you think.

> 
> With that done I think we should first switch over TTM and all
> drivers 
> using it to drm_exec as part of it's context object.

So are you ok with adding an optional drm_exec pointer in the
ttm_operation_ctx for this? (That was my plan moving forward).

However, when that has been added, I think it makes sense to leave to
the driver author to port their validation loops and bo allocation over
to using drm_exec. While we made sure the drm_exec object was indeed
passed to the validation helper in the drm_gpuvm code, I'm not sure
everybody actually includes their validation and bo allocation (for
example page-table-bos) in their drm_exec while_not_all_locked() loop,
and I think it's reasonable to require the "port the driver over" to be
an optional but strongly recommended driver effort. If the driver sets
ctx->drm_exec to NULL, it will fallback to current behaviour.

> 
> Then I would switch over to using LRU hitches for both swapping and 
> eviction.
> 
> And when that's finally done we can take a look into the partial
> shmem 
> swapping :)
> 
> And Felix is really (and mean *really*) looking forward to the
> partial 
> shmem swapping as well.

While the LRU walker helper introduced in patch 8 has drm_exec support,
shrinkers don't require it, since they are always trylocking. (However
being able to "evict" system to swap directly in the validation stage
using drm_exec locking is probably something we should support). 

That's why I opted for implementing shrinking before exhaustive
eviction. But if you insist we can do it the other way around. Most of
what's needed is already in the patches.

/Thomas


> 
> Regards,
> Christian.
> 
> Am 16.04.24 um 12:07 schrieb Thomas Hellström:
> > 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
> > 
> > for patch 1-4, which IMO still could be reviewed and pushed as a
> > separate series.
> > 
> > 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.
> > 
> > In any case, patch 1-4 are better described in their separate
> > series.
> > (RFC is removed for those).
> > 
> > Patch 5 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 6 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 7 Adds a simple error injection to the above code to help
> > increase
> > test coverage.
> > 
> > Patch 8 introduces a LRU walk helper for eviction and shrinking.
> > It's
> > currently xe-only but not xe-specific and can easily be moved to
> > TTM when
> > used by more than one driver or when eviction is implemented using
> > it.
> > 
> > Patch 9 introduces a helper callback for shrinking (Also ready to
> > be
> > moved to TTM) and an xe-specific shrinker implementation. It also
> > adds a kunit test to test the shrinker functionality by trying to
> > allocate twice the available amount of RAM as buffer objects. If
> > there
> > is no swap-space available, the buffer objects are marked
> > purgeable.
> > 
> > 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
> > 
> > Cc: Somalapuram Amaranath <Amaranath.Somalapuram@amd.com>
> > Cc: Christian König <christian.koenig@amd.com>
> > Cc: <dri-devel@lists.freedesktop.org>
> > 
> > Thomas Hellström (8):
> >    drm/ttm: Allow TTM LRU list nodes of different types
> >    drm/ttm: Use LRU hitches
> >    drm/ttm, drm/amdgpu, drm/xe: Consider hitch moves within bulk
> > sublist
> >      moves
> >    drm/ttm: Allow continued swapout after -ENOSPC falure
> >    drm/ttm: Add a virtual base class for graphics memory backup
> >    drm/ttm/pool: Provide a helper to shrink pages.
> >    drm/xe, drm/ttm: Provide a generic LRU walker helper
> >    drm/xe: Add a shrinker for xe bos
> > 
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c |   4 +
> >   drivers/gpu/drm/ttm/Makefile           |   2 +-
> >   drivers/gpu/drm/ttm/ttm_backup_shmem.c | 137 +++++++++
> >   drivers/gpu/drm/ttm/ttm_bo.c           |   1 +
> >   drivers/gpu/drm/ttm/ttm_device.c       |  33 ++-
> >   drivers/gpu/drm/ttm/ttm_pool.c         | 391
> > ++++++++++++++++++++++++-
> >   drivers/gpu/drm/ttm/ttm_resource.c     | 231 ++++++++++++---
> >   drivers/gpu/drm/ttm/ttm_tt.c           |  34 +++
> >   drivers/gpu/drm/xe/Makefile            |   2 +
> >   drivers/gpu/drm/xe/xe_bo.c             | 123 ++++++--
> >   drivers/gpu/drm/xe/xe_bo.h             |   3 +
> >   drivers/gpu/drm/xe/xe_device.c         |   8 +
> >   drivers/gpu/drm/xe/xe_device_types.h   |   2 +
> >   drivers/gpu/drm/xe/xe_shrinker.c       | 237 +++++++++++++++
> >   drivers/gpu/drm/xe/xe_shrinker.h       |  18 ++
> >   drivers/gpu/drm/xe/xe_ttm_helpers.c    | 224 ++++++++++++++
> >   drivers/gpu/drm/xe/xe_ttm_helpers.h    |  63 ++++
> >   drivers/gpu/drm/xe/xe_vm.c             |   4 +
> >   include/drm/ttm/ttm_backup.h           | 136 +++++++++
> >   include/drm/ttm/ttm_device.h           |   2 +
> >   include/drm/ttm/ttm_pool.h             |   4 +
> >   include/drm/ttm/ttm_resource.h         |  96 +++++-
> >   include/drm/ttm/ttm_tt.h               |  19 ++
> >   23 files changed, 1683 insertions(+), 91 deletions(-)
> >   create mode 100644 drivers/gpu/drm/ttm/ttm_backup_shmem.c
> >   create mode 100644 drivers/gpu/drm/xe/xe_shrinker.c
> >   create mode 100644 drivers/gpu/drm/xe/xe_shrinker.h
> >   create mode 100644 drivers/gpu/drm/xe/xe_ttm_helpers.c
> >   create mode 100644 drivers/gpu/drm/xe/xe_ttm_helpers.h
> >   create mode 100644 include/drm/ttm/ttm_backup.h
> > 
>