* [PATCH] mm/madvise: swap in CoW'd MAP_PRIVATE-file mappings on MADV_WILLNEED @ 2026-09-04 15:12 Lorenzo Stoakes (ARM) 2026-09-04 15:24 ` Pedro Falcato 0 siblings, 1 reply; 3+ messages in thread From: Lorenzo Stoakes (ARM) @ 2026-09-04 15:12 UTC (permalink / raw) To: Andrew Morton, Liam R. Howlett, David Hildenbrand, Vlastimil Babka, Jann Horn Cc: linux-mm, linux-kernel, Mike Kaplinskiy, zhaozhengzhuo, Lorenzo Stoakes (ARM) Currently MADV_WILLNEED treats file-backed and pure anonymous mappings entirely separately - using POSIX_FADV_WILLNEED (equivalent of a readahead) for the former and a tree walk and swap in to swap cache for the latter. MAP_PRIVATE-file backed mappings straddle the two and currently get treated as if they were purely file-backed, meaning any swapped out private pages remain swapped out. Resolve the issue by explicitly checking for CoW'd MAP_PRIVATE-file backed mappings and performing both walks in this case. Since the logic checks for vma->anon_vma this means un-CoW'd MAP_PRIVATE-file backed mappings retain only the single file walk. Reported-by: Mike Kaplinskiy <mike@recall.ai> Closes: https://lore.kernel.org/all/CABeknB_S2XJSHFgnHdgnN0rjzHhH4oQJs_APq9fvxHztQ_pgiA@mail.gmail.com/ Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org> --- mm/madvise.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/madvise.c b/mm/madvise.c index 73c2901b9adb..d0510dd49dde 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -297,10 +297,12 @@ static long madvise_willneed(struct madvise_behavior *madv_behavior) loff_t offset; #ifdef CONFIG_SWAP - if (!file) { + if (!file || (vma_is_cow_mapping(vma) && vma->anon_vma)) { walk_page_range_vma(vma, start, end, &swapin_walk_ops, vma); lru_add_drain(); /* Push any new pages onto the LRU now */ - return 0; + + if (!file) + return 0; } if (shmem_mapping(file->f_mapping)) { --- base-commit: e3b5239afe1b8f0194db7436b17c33e94c1988c4 change-id: 20260903-madv-will-need-map-private-125e3e2f70c7 Best regards, -- Lorenzo Stoakes (ARM) <ljs@kernel.org> ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] mm/madvise: swap in CoW'd MAP_PRIVATE-file mappings on MADV_WILLNEED 2026-09-04 15:12 [PATCH] mm/madvise: swap in CoW'd MAP_PRIVATE-file mappings on MADV_WILLNEED Lorenzo Stoakes (ARM) @ 2026-09-04 15:24 ` Pedro Falcato 2026-09-04 16:01 ` Lorenzo Stoakes (ARM) 0 siblings, 1 reply; 3+ messages in thread From: Pedro Falcato @ 2026-09-04 15:24 UTC (permalink / raw) To: Lorenzo Stoakes (ARM) Cc: Andrew Morton, Liam R. Howlett, David Hildenbrand, Vlastimil Babka, Jann Horn, linux-mm, linux-kernel, Mike Kaplinskiy, zhaozhengzhuo On Fri, Sep 04, 2026 at 04:12:53PM +0100, Lorenzo Stoakes (ARM) wrote: > Currently MADV_WILLNEED treats file-backed and pure anonymous mappings > entirely separately - using POSIX_FADV_WILLNEED (equivalent of a readahead) > for the former and a tree walk and swap in to swap cache for the latter. > > MAP_PRIVATE-file backed mappings straddle the two and currently get treated > as if they were purely file-backed, meaning any swapped out private pages > remain swapped out. > > Resolve the issue by explicitly checking for CoW'd MAP_PRIVATE-file backed > mappings and performing both walks in this case. > > Since the logic checks for vma->anon_vma this means un-CoW'd > MAP_PRIVATE-file backed mappings retain only the single file walk. > > Reported-by: Mike Kaplinskiy <mike@recall.ai> > Closes: https://lore.kernel.org/all/CABeknB_S2XJSHFgnHdgnN0rjzHhH4oQJs_APq9fvxHztQ_pgiA@mail.gmail.com/ > Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org> > --- > mm/madvise.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/mm/madvise.c b/mm/madvise.c > index 73c2901b9adb..d0510dd49dde 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -297,10 +297,12 @@ static long madvise_willneed(struct madvise_behavior *madv_behavior) > loff_t offset; > > #ifdef CONFIG_SWAP > - if (!file) { > + if (!file || (vma_is_cow_mapping(vma) && vma->anon_vma)) { Couldn't this all be simplified to if (vma->anon_vma) { ? swapin needs anon pages to have been faulted-in. Non-cow mappings won't have an anon_vma, nor will fully empty anonymous VMAs (and that's fine). Right? Regardless, looks cromulent Reviewed-by: Pedro Falcato <pfalcato@suse.de> -- Pedro ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] mm/madvise: swap in CoW'd MAP_PRIVATE-file mappings on MADV_WILLNEED 2026-09-04 15:24 ` Pedro Falcato @ 2026-09-04 16:01 ` Lorenzo Stoakes (ARM) 0 siblings, 0 replies; 3+ messages in thread From: Lorenzo Stoakes (ARM) @ 2026-09-04 16:01 UTC (permalink / raw) To: Pedro Falcato Cc: Andrew Morton, Liam R. Howlett, David Hildenbrand, Vlastimil Babka, Jann Horn, linux-mm, linux-kernel, Mike Kaplinskiy, zhaozhengzhuo On Fri, Sep 04, 2026 at 04:24:59PM +0100, Pedro Falcato wrote: > On Fri, Sep 04, 2026 at 04:12:53PM +0100, Lorenzo Stoakes (ARM) wrote: > > Currently MADV_WILLNEED treats file-backed and pure anonymous mappings > > entirely separately - using POSIX_FADV_WILLNEED (equivalent of a readahead) > > for the former and a tree walk and swap in to swap cache for the latter. > > > > MAP_PRIVATE-file backed mappings straddle the two and currently get treated > > as if they were purely file-backed, meaning any swapped out private pages > > remain swapped out. > > > > Resolve the issue by explicitly checking for CoW'd MAP_PRIVATE-file backed > > mappings and performing both walks in this case. > > > > Since the logic checks for vma->anon_vma this means un-CoW'd > > MAP_PRIVATE-file backed mappings retain only the single file walk. > > > > Reported-by: Mike Kaplinskiy <mike@recall.ai> > > Closes: https://lore.kernel.org/all/CABeknB_S2XJSHFgnHdgnN0rjzHhH4oQJs_APq9fvxHztQ_pgiA@mail.gmail.com/ > > Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org> > > --- > > mm/madvise.c | 6 ++++-- > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > diff --git a/mm/madvise.c b/mm/madvise.c > > index 73c2901b9adb..d0510dd49dde 100644 > > --- a/mm/madvise.c > > +++ b/mm/madvise.c > > @@ -297,10 +297,12 @@ static long madvise_willneed(struct madvise_behavior *madv_behavior) > > loff_t offset; > > > > #ifdef CONFIG_SWAP > > - if (!file) { > > + if (!file || (vma_is_cow_mapping(vma) && vma->anon_vma)) { > > Couldn't this all be simplified to > > if (vma->anon_vma) { > > ? swapin needs anon pages to have been faulted-in. Non-cow mappings won't > have an anon_vma, nor will fully empty anonymous VMAs (and that's fine). > Right? Hmm good point :) Though the if (!file) return 0; Would have to be outside of the block to avoid an anon unfaulted (nop) from being skipped. And it's a real improvement to have unfaulted anon skip... But I find that version is documenting what's going on a lot less. Since both anon and MAP_PRIVATE file-backed are CoW mappings we could just reference that. Andrew - could you swap the patch out in-place with below? Thanks! Cheers, Lorenzo ----8<---- From a706374a1186b6b4409a0e760e8728bcadba0c96 Mon Sep 17 00:00:00 2001 From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org> Date: Thu, 3 Sep 2026 20:08:39 +0100 Subject: [PATCH] mm/madvise: swap in CoW'd MAP_PRIVATE-file mappings on MADV_WILLNEED Currently MADV_WILLNEED treats file-backed and pure anonymous mappings entirely separately - using POSIX_FADV_WILLNEED (equivalent of a readahead) for the former and a tree walk and swap in to swap cache for the latter. MAP_PRIVATE-file backed mappings straddle the two and currently get treated as if they were purely file-backed, meaning any swapped out private pages remain swapped out. Resolve the issue by explicitly checking for CoW'd MAP_PRIVATE-file backed mappings and performing both walks in this case. Since the logic checks for vma->anon_vma this means un-CoW'd MAP_PRIVATE-file backed mappings retain only the single file walk. Reported-by: Mike Kaplinskiy <mike@recall.ai> Closes: https://lore.kernel.org/all/CABeknB_S2XJSHFgnHdgnN0rjzHhH4oQJs_APq9fvxHztQ_pgiA@mail.gmail.com/ Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org> --- mm/madvise.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/madvise.c b/mm/madvise.c index 73c2901b9adb..963337f93a7a 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -297,11 +297,12 @@ static long madvise_willneed(struct madvise_behavior *madv_behavior) loff_t offset; #ifdef CONFIG_SWAP - if (!file) { + if (vma_is_cow_mapping(vma) && vma->anon_vma) { walk_page_range_vma(vma, start, end, &swapin_walk_ops, vma); lru_add_drain(); /* Push any new pages onto the LRU now */ - return 0; } + if (!file) + return 0; if (shmem_mapping(file->f_mapping)) { shmem_swapin_range(vma, start, end, file->f_mapping); -- 2.55.0 ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2026-09-04 16:01 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2026-09-04 15:12 [PATCH] mm/madvise: swap in CoW'd MAP_PRIVATE-file mappings on MADV_WILLNEED Lorenzo Stoakes (ARM) 2026-09-04 15:24 ` Pedro Falcato 2026-09-04 16:01 ` Lorenzo Stoakes (ARM)
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