On Fri, Feb 27, 2026 at 09:08:40PM +0100, David Hildenbrand (Arm) wrote: > 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]>
This is another nice change. I have some tweak suggestions below, but past experience suggests to me it's quite possible you do what I ask in subsequent patches, will see :) Anyway overall LGTM, so: Reviewed-by: Lorenzo Stoakes (Oracle) <[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) Not sure if you fix up later, but we should probably change this function to should_skip_cows() to keep everything consistent, otherwise this is a bit weird and confusing. > { > /* 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; Not sure if you clean up later, but seems sensible to cascade the change into the local boolean here. > if (last_index < first_index) > last_index = ULONG_MAX; > > -- > 2.43.0 >
