migrate_misplaced_folio_prepare() can be called from a
context where VMA isn't available. Allow the migration
to work from such contexts too.
Signed-off-by: Bharata B Rao <bharata@amd.com>
---
mm/migrate.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/mm/migrate.c b/mm/migrate.c
index fb19a18892c8..5b21856a0dd0 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2639,7 +2639,8 @@ static struct folio *alloc_misplaced_dst_folio(struct folio *src,
/*
* Prepare for calling migrate_misplaced_folio() by isolating the folio if
- * permitted. Must be called with the PTL still held.
+ * permitted. Must be called with the PTL still held if called with a non-NULL
+ * vma.
*/
int migrate_misplaced_folio_prepare(struct folio *folio,
struct vm_area_struct *vma, int node)
@@ -2656,7 +2657,7 @@ int migrate_misplaced_folio_prepare(struct folio *folio,
* See folio_likely_mapped_shared() on possible imprecision
* when we cannot easily detect if a folio is shared.
*/
- if ((vma->vm_flags & VM_EXEC) &&
+ if (vma && (vma->vm_flags & VM_EXEC) &&
folio_likely_mapped_shared(folio))
return -EACCES;
--
2.34.1On 3/6/25 16:45, Bharata B Rao wrote: > migrate_misplaced_folio_prepare() can be called from a > context where VMA isn't available. Allow the migration > to work from such contexts too. > > Signed-off-by: Bharata B Rao <bharata@amd.com> > --- > mm/migrate.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index fb19a18892c8..5b21856a0dd0 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -2639,7 +2639,8 @@ static struct folio *alloc_misplaced_dst_folio(struct folio *src, > > /* > * Prepare for calling migrate_misplaced_folio() by isolating the folio if > - * permitted. Must be called with the PTL still held. > + * permitted. Must be called with the PTL still held if called with a non-NULL > + * vma. > */ > int migrate_misplaced_folio_prepare(struct folio *folio, > struct vm_area_struct *vma, int node) > @@ -2656,7 +2657,7 @@ int migrate_misplaced_folio_prepare(struct folio *folio, > * See folio_likely_mapped_shared() on possible imprecision > * when we cannot easily detect if a folio is shared. > */ > - if ((vma->vm_flags & VM_EXEC) && > + if (vma && (vma->vm_flags & VM_EXEC) && > folio_likely_mapped_shared(folio)) > return -EACCES; > In the worst case, the absence of the vma would mean that we try to isolate and migrate a shared folio with executable pages. Are those a key target for the hot page migration? Balbir
On 24-Mar-25 8:25 AM, Balbir Singh wrote: > On 3/6/25 16:45, Bharata B Rao wrote: >> migrate_misplaced_folio_prepare() can be called from a >> context where VMA isn't available. Allow the migration >> to work from such contexts too. >> >> Signed-off-by: Bharata B Rao <bharata@amd.com> >> --- >> mm/migrate.c | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index fb19a18892c8..5b21856a0dd0 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -2639,7 +2639,8 @@ static struct folio *alloc_misplaced_dst_folio(struct folio *src, >> >> /* >> * Prepare for calling migrate_misplaced_folio() by isolating the folio if >> - * permitted. Must be called with the PTL still held. >> + * permitted. Must be called with the PTL still held if called with a non-NULL >> + * vma. >> */ >> int migrate_misplaced_folio_prepare(struct folio *folio, >> struct vm_area_struct *vma, int node) >> @@ -2656,7 +2657,7 @@ int migrate_misplaced_folio_prepare(struct folio *folio, >> * See folio_likely_mapped_shared() on possible imprecision >> * when we cannot easily detect if a folio is shared. >> */ >> - if ((vma->vm_flags & VM_EXEC) && >> + if (vma && (vma->vm_flags & VM_EXEC) && >> folio_likely_mapped_shared(folio)) >> return -EACCES; >> > > In the worst case, the absence of the vma would mean that we try to isolate > and migrate a shared folio with executable pages. Are those a key target for the > hot page migration? I don't think they are a key target for hot page migration, but if shared executable pages (like shared library pages) have ended up in lower tier, it doesn't hurt to get them promoted to top tier, I would think. Regards, Bharata.
On Thu, Mar 06, 2025 at 11:15:29AM +0530, Bharata B Rao wrote: > migrate_misplaced_folio_prepare() can be called from a > context where VMA isn't available. Allow the migration > to work from such contexts too. > > Signed-off-by: Bharata B Rao <bharata@amd.com> I have a similar patch in the unmapped pagecache RFC we may also need this: https://lore.kernel.org/linux-mm/20250107000346.1338481-4-gourry@gourry.net/ May be worth just pulling these ahead to avoid conflict. ~Gregory
On Thu, Mar 06, 2025 at 12:24:16PM -0500, Gregory Price wrote: > On Thu, Mar 06, 2025 at 11:15:29AM +0530, Bharata B Rao wrote: > > migrate_misplaced_folio_prepare() can be called from a > > context where VMA isn't available. Allow the migration > > to work from such contexts too. > > > > Signed-off-by: Bharata B Rao <bharata@amd.com> > > I have a similar patch in the unmapped pagecache RFC > > we may also need this: > https://lore.kernel.org/linux-mm/20250107000346.1338481-4-gourry@gourry.net/ > > May be worth just pulling these ahead to avoid conflict. Or not putting them in at all because this whole thing is a magnificent waste of time?
On Thu, Mar 06, 2025 at 05:45:34PM +0000, Matthew Wilcox wrote: > On Thu, Mar 06, 2025 at 12:24:16PM -0500, Gregory Price wrote: > > we may also need this: > > https://lore.kernel.org/linux-mm/20250107000346.1338481-4-gourry@gourry.net/ > > > > May be worth just pulling these ahead to avoid conflict. > > Or not putting them in at all because this whole thing is a magnificent > waste of time? Divorced from the tiering mechanisms, is making misplaced migration able to migrate unmapped pages not generally useful? ~Gregory
On Thu, Mar 06, 2025 at 01:19:41PM -0500, Gregory Price wrote: > On Thu, Mar 06, 2025 at 05:45:34PM +0000, Matthew Wilcox wrote: > > On Thu, Mar 06, 2025 at 12:24:16PM -0500, Gregory Price wrote: > > > we may also need this: > > > https://lore.kernel.org/linux-mm/20250107000346.1338481-4-gourry@gourry.net/ > > > > > > May be worth just pulling these ahead to avoid conflict. > > > > Or not putting them in at all because this whole thing is a magnificent > > waste of time? > > Divorced from the tiering mechanisms, is making misplaced migration able > to migrate unmapped pages not generally useful? The only thing I can think of is if you have a process or set of processes on node A calling read() and the file is cached on node B. But in order to decide if the page is on the wrong node, you'd need to track a lot of information about which nodes the page is being accessed from. Which is probably why we've never bothered to do it. This is not a large patch for you to carry as part of your patchset. There's nothing intrinsically wrong with it; it just has no users in mainline and no real prospect of any being added soon.
On Thu, Mar 06, 2025 at 06:42:10PM +0000, Matthew Wilcox wrote: > On Thu, Mar 06, 2025 at 01:19:41PM -0500, Gregory Price wrote: > > Divorced from the tiering mechanisms, is making misplaced migration able > > to migrate unmapped pages not generally useful? > > The only thing I can think of is if you have a process or set of > processes on node A calling read() and the file is cached on node B. > But in order to decide if the page is on the wrong node, you'd need > to track a lot of information about which nodes the page is being > accessed from. Which is probably why we've never bothered to do it. > > This is not a large patch for you to carry as part of your patchset. > There's nothing intrinsically wrong with it; it just has no users in > mainline and no real prospect of any being added soon. That's fair, I'm just tracking 3-4 different RFCs that are going to butt up against this, so wanted to assess whether getting the patches out ahead would save some strife. ~Gregory
On 06.03.25 06:45, Bharata B Rao wrote: > migrate_misplaced_folio_prepare() can be called from a > context where VMA isn't available. Allow the migration > to work from such contexts too. I was initially confused about "can be called", because it can't Consider phrasing it as "We want to make use of alloc_misplaced_dst_folio() in context where we don't have VMA information available. To prepare for that ..." > > Signed-off-by: Bharata B Rao <bharata@amd.com> > --- > mm/migrate.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index fb19a18892c8..5b21856a0dd0 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -2639,7 +2639,8 @@ static struct folio *alloc_misplaced_dst_folio(struct folio *src, > > /* > * Prepare for calling migrate_misplaced_folio() by isolating the folio if > - * permitted. Must be called with the PTL still held. > + * permitted. Must be called with the PTL still held if called with a non-NULL > + * vma. > */ > int migrate_misplaced_folio_prepare(struct folio *folio, > struct vm_area_struct *vma, int node) > @@ -2656,7 +2657,7 @@ int migrate_misplaced_folio_prepare(struct folio *folio, > * See folio_likely_mapped_shared() on possible imprecision > * when we cannot easily detect if a folio is shared. > */ > - if ((vma->vm_flags & VM_EXEC) && > + if (vma && (vma->vm_flags & VM_EXEC) && > folio_likely_mapped_shared(folio)) > return -EACCES; > -- Cheers, David / dhildenb
On 06-Mar-25 5:43 PM, David Hildenbrand wrote: > On 06.03.25 06:45, Bharata B Rao wrote: >> migrate_misplaced_folio_prepare() can be called from a >> context where VMA isn't available. Allow the migration >> to work from such contexts too. > > I was initially confused about "can be called", because it can't > > Consider phrasing it as "We want to make use of > alloc_misplaced_dst_folio() in context where we don't have VMA > information available. To prepare for that ..." Yes, that would be the right wording. Thanks, Bharata.
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