The current semantics are confusing: simply because someone specifies an empty zap_detail struct suddenly makes should_zap_cows() behave differently. The default should be to also zap CoW'ed anonymous pages.
Really only unmap_mapping_pages() and friends want to skip zapping of these anon folios. So let's invert the meaning; turn the confusing "reclaim_pt" check that overrides other properties in should_zap_cows() into a safety check. Note that the only caller that sets reclaim_pt=true is madvise_dontneed_single_vma(), which wants to zap any pages. Signed-off-by: David Hildenbrand (Arm) <[email protected]> --- include/linux/mm.h | 2 +- mm/madvise.c | 1 - mm/memory.c | 12 ++++++------ 3 files changed, 7 insertions(+), 8 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index d3ef586ee1c0..21b67c203e62 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2798,7 +2798,7 @@ extern void pagefault_out_of_memory(void); */ struct zap_details { struct folio *single_folio; /* Locked folio to be unmapped */ - bool even_cows; /* Zap COWed private pages too? */ + bool skip_cows; /* Do not zap COWed private pages */ bool reclaim_pt; /* Need reclaim page tables? */ zap_flags_t zap_flags; /* Extra flags for zapping */ }; diff --git a/mm/madvise.c b/mm/madvise.c index 557a360f7919..b51f216934f3 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -853,7 +853,6 @@ static long madvise_dontneed_single_vma(struct madvise_behavior *madv_behavior) struct madvise_behavior_range *range = &madv_behavior->range; struct zap_details details = { .reclaim_pt = true, - .even_cows = true, }; zap_page_range_single_batched( diff --git a/mm/memory.c b/mm/memory.c index fdcd2abf29c2..7d7c24c6917c 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1554,11 +1554,13 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) static inline bool should_zap_cows(struct zap_details *details) { /* By default, zap all pages */ - if (!details || details->reclaim_pt) + if (!details) return true; + VM_WARN_ON_ONCE(details->skip_cows && details->reclaim_pt); + /* Or, we zap COWed pages only if the caller wants to */ - return details->even_cows; + return !details->skip_cows; } /* Decides whether we should zap this folio with the folio pointer specified */ @@ -2149,8 +2151,6 @@ void unmap_vmas(struct mmu_gather *tlb, struct unmap_desc *unmap) struct mmu_notifier_range range; struct zap_details details = { .zap_flags = ZAP_FLAG_DROP_MARKER | ZAP_FLAG_UNMAP, - /* Careful - we need to zap private pages too! */ - .even_cows = true, }; vma = unmap->first; @@ -4282,7 +4282,7 @@ void unmap_mapping_folio(struct folio *folio) first_index = folio->index; last_index = folio_next_index(folio) - 1; - details.even_cows = false; + details.skip_cows = true; details.single_folio = folio; details.zap_flags = ZAP_FLAG_DROP_MARKER; @@ -4312,7 +4312,7 @@ void unmap_mapping_pages(struct address_space *mapping, pgoff_t start, pgoff_t first_index = start; pgoff_t last_index = start + nr - 1; - details.even_cows = even_cows; + details.skip_cows = !even_cows; if (last_index < first_index) last_index = ULONG_MAX; -- 2.43.0
