Re: [PATCH] mm: synchronize with PTE table reclaim for all folio sizes

[Pedro Falcato]

On Thu, Nov 05, 2026 at 10:56:28AM +0800, Baolin Wang wrote:
> Similar to commit 243cf1f67b36 ("mm: memory: fix truncation removing mapped
> folios"), the '!pmd_present()' check in page_vma_mapped_walk() can also race
> with concurrent page table reclamation via zap_empty_pte_table().
> 
> page_vma_mapped_walk() is used by many functions including try_to_unmap(),
> try_to_migrate(), folio_mkclean(), pfn_mkclean_range(), remove_migration_ptes(),
> page_mapped_in_vma(), and mapping_wrprotect_range(). Except for try_to_unmap()
> and try_to_migrate(), the other callers do not perform post-walk accounting
> checks, so the race has no observable impact on them.
> 
> For migration, the race can cause unnecessary retries. For reclaim via
> try_to_unmap(), the race can cause failure to reclaim a folio that is in
> fact already unmapped (as shown below), which may lead to unexpected OOM
> or increased refaults.

This is very handwavy. Do you have numbers? Does this actually make sense?

-- 
Pedro