mm/madvise.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
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>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
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
On 9/4/26 18:01, Lorenzo Stoakes (ARM) wrote:
> On Fri, Sep 04, 2026 at 04:24:59PM +0100, Pedro Falcato wrote:
> 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>
Acked-by: Vlastimil Babka (SUSE) <vbabka@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
On Fri, Sep 04, 2026 at 05:01:37PM +0100, Lorenzo Stoakes (ARM) wrote:
> 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>
LGTM, thanks!
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
--
Pedro
> 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!
A proper v2 would have been nice ;)
(and would trigger sashiko and friends properly)
>
> 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;
>
LGTM
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
--
Cheers,
David
On Mon, Sep 07, 2026 at 01:51:20PM +0200, David Hildenbrand (Arm) wrote:
> > 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!
>
> A proper v2 would have been nice ;)
>
> (and would trigger sashiko and friends properly)
Ack, though it's kinda obviously functionally equivalent (or so I felt :P).
I had a local LLM check it FWIW.
>
> >
> > 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;
> >
> LGTM
>
> Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Thanks!
>
> --
> Cheers,
>
> David
--
Cheers, Lorenzo
On Fri, 4 Sep 2026 17:01:37 +0100 "Lorenzo Stoakes (ARM)" <ljs@kernel.org> wrote: > Andrew - could you swap the patch out in-place with below? Thanks! > np. > 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> The failure mode looks pretty obscure, so I'm thinking that no backport is needed.
On Sat, Sep 05, 2026 at 05:17:57PM -0700, Andrew Morton wrote: > On Fri, 4 Sep 2026 17:01:37 +0100 "Lorenzo Stoakes (ARM)" <ljs@kernel.org> wrote: > > > Andrew - could you swap the patch out in-place with below? Thanks! > > > > np. > > > 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> > > The failure mode looks pretty obscure, so I'm thinking that no backport > is needed. Well it's not even really a failure mode so much as a 'known limitation' :) So yeah agreed. -- Cheers, Lorenzo
On 9/7/26 14:32, Lorenzo Stoakes (ARM) wrote: > On Sat, Sep 05, 2026 at 05:17:57PM -0700, Andrew Morton wrote: >> On Fri, 4 Sep 2026 17:01:37 +0100 "Lorenzo Stoakes (ARM)" <ljs@kernel.org> wrote: >> >> > Andrew - could you swap the patch out in-place with below? Thanks! >> > >> >> np. >> >> > 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> >> >> The failure mode looks pretty obscure, so I'm thinking that no backport >> is needed. > > Well it's not even really a failure mode so much as a 'known limitation' :) > So yeah agreed. Yeah, as we know madvise() just an advice after all, the kernel is free to ignore it :) (MADV_DONTNEED and friends enter the chat) > -- > Cheers, Lorenzo
On Mon, Sep 07, 2026 at 05:09:34PM +0200, Vlastimil Babka (SUSE) wrote: > On 9/7/26 14:32, Lorenzo Stoakes (ARM) wrote: > > On Sat, Sep 05, 2026 at 05:17:57PM -0700, Andrew Morton wrote: > >> On Fri, 4 Sep 2026 17:01:37 +0100 "Lorenzo Stoakes (ARM)" <ljs@kernel.org> wrote: > >> > >> > Andrew - could you swap the patch out in-place with below? Thanks! > >> > > >> > >> np. > >> > >> > 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> > >> > >> The failure mode looks pretty obscure, so I'm thinking that no backport > >> is needed. > > > > Well it's not even really a failure mode so much as a 'known limitation' :) > > So yeah agreed. > > Yeah, as we know madvise() just an advice after all, the kernel is free to > ignore it :) > > (MADV_DONTNEED and friends enter the chat) Haha yeah, another brilliant footgun invented by the proud folks at kernel mm, catch us next time with some prctl's and BPF APIs! ;) > > > -- > > Cheers, Lorenzo > -- Cheers, Lorenzo
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