Re: [PATCH 1/4] drm/ttm: Don't mark backed-up shmem folios accessed

[Matthew Brost <matthew.brost@intel.com>]

On Wed, Nov 04, 2026 at 09:13:28PM +0100, Thomas Hellström wrote:
> ttm_backup_backup_folio() unconditionally called folio_mark_accessed()
> on the freshly populated shmem folio before copying the BO's data into
> it. This path is only reached from a shrinker, i.e. precisely when the
> system has already decided it needs memory back, and the whole point
> of backing a page up into shmem is to let core mm reclaim it through
> the normal swap/writeback path instead of keeping it pinned as TTM
> memory.
> 
> Marking the folio accessed works against that: it sets the referenced
> bit / promotes the folio on the LRU, so a later reclaim scan gives it
> a second chance (or skips it) instead of reclaiming it on sight. This
> is actively counter-productive even when the writeback backup flag is
> set to synchronously flush the folio's content via shmem_write_folio():
> writeback only clears the dirty bit, it does not free the page, so an
> accessed folio just sits there, clean and resident, protected from the
> very reclaim pass it was written back for.
> 
> Drop the folio_mark_accessed() call so these folios decay through
> normal LRU aging and become immediate reclaim candidates once written
> back (or once picked up by the system's own asynchronous laundering),
> instead of being artificially kept warm.
> 
> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> ---
>  drivers/gpu/drm/ttm/ttm_backup.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_backup.c b/drivers/gpu/drm/ttm/ttm_backup.c
> index 0c2d53a13b2a..9589067ad8cf 100644
> --- a/drivers/gpu/drm/ttm/ttm_backup.c
> +++ b/drivers/gpu/drm/ttm/ttm_backup.c
> @@ -149,7 +149,6 @@ ttm_backup_backup_folio(struct file *backup, struct folio *folio,
>  		to_nr = min_t(int, nr_pages - i,
>  			      folio_next_index(to_folio) - (idx + i));
>  
> -		folio_mark_accessed(to_folio);
>  		folio_lock(to_folio);
>  		folio_mark_dirty(to_folio);
>  
> -- 
> 2.56.0
>