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[PATCH 3/3] alloc_tag: avoid warnings when freeing non-compound "tail" pages

Suren Baghdasaryan posted 3 patches 5 months ago
There is a newer version of this series
[PATCH 3/3] alloc_tag: avoid warnings when freeing non-compound "tail" pages
Posted by Suren Baghdasaryan 5 months ago 
When freeing "tail" pages of a non-compount high-order page, we properly
subtract the allocation tag counters, however later when these pages are
released, alloc_tag_sub() will issue warnings because tags for these pages
are NULL.
This issue was originally anticipated by Vlastimil in his review [1] and
then recently reported by David.
Prevent warnings by marking the tags empty.

[1] https://lore.kernel.org/all/6db0f0c8-81cb-4d04-9560-ba73d63db4b8@suse.cz/

Suggested-by: David Wang <00107082@163.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 mm/page_alloc.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1760346bbd24..d21a411e807e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5240,9 +5240,16 @@ static void ___free_pages(struct page *page, unsigned int order,
 		__free_frozen_pages(page, order, fpi_flags);
 	else if (!head) {
 		pgalloc_tag_sub_pages(tag, (1 << order) - 1);
-		while (order-- > 0)
+		while (order-- > 0) {
+			/*
+			 * The "tail" pages of this non-compound high-order
+			 * page will have no code tags, so to avoid warnings
+			 * mark them as empty.
+			 */
+			clear_page_tag_ref(page + (1 << order));
 			__free_frozen_pages(page + (1 << order), order,
 					    fpi_flags);
+		}
 	}
 }
 
-- 
2.51.0.384.g4c02a37b29-goog
Re: [PATCH 3/3] alloc_tag: avoid warnings when freeing non-compound "tail" pages
Posted by Shakeel Butt 5 months ago 
On Tue, Sep 09, 2025 at 04:34:09PM -0700, Suren Baghdasaryan wrote:
> When freeing "tail" pages of a non-compount high-order page, we properly
> subtract the allocation tag counters, however later when these pages are
> released, alloc_tag_sub() will issue warnings because tags for these pages
> are NULL.
> This issue was originally anticipated by Vlastimil in his review [1] and
> then recently reported by David.
> Prevent warnings by marking the tags empty.
> 
> [1] https://lore.kernel.org/all/6db0f0c8-81cb-4d04-9560-ba73d63db4b8@suse.cz/
> 
> Suggested-by: David Wang <00107082@163.com>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Re: [PATCH 3/3] alloc_tag: avoid warnings when freeing non-compound "tail" pages
Posted by Shakeel Butt 5 months ago 
On Tue, Sep 09, 2025 at 04:34:09PM -0700, Suren Baghdasaryan wrote:
> When freeing "tail" pages of a non-compount high-order page, we properly
> subtract the allocation tag counters, however later when these pages are
> released, alloc_tag_sub() will issue warnings because tags for these pages
> are NULL.
> This issue was originally anticipated by Vlastimil in his review [1] and
> then recently reported by David.
> Prevent warnings by marking the tags empty.
> 
> [1] https://lore.kernel.org/all/6db0f0c8-81cb-4d04-9560-ba73d63db4b8@suse.cz/
> 
> Suggested-by: David Wang <00107082@163.com>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
>  mm/page_alloc.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 1760346bbd24..d21a411e807e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5240,9 +5240,16 @@ static void ___free_pages(struct page *page, unsigned int order,
>  		__free_frozen_pages(page, order, fpi_flags);
>  	else if (!head) {
>  		pgalloc_tag_sub_pages(tag, (1 << order) - 1);
> -		while (order-- > 0)
> +		while (order-- > 0) {
> +			/*
> +			 * The "tail" pages of this non-compound high-order
> +			 * page will have no code tags, so to avoid warnings
> +			 * mark them as empty.
> +			 */
> +			clear_page_tag_ref(page + (1 << order));

Do we need something similar for the release_pages() code path or is it
happening already?

>  			__free_frozen_pages(page + (1 << order), order,
>  					    fpi_flags);
> +		}
>  	}
>  }
>  
> -- 
> 2.51.0.384.g4c02a37b29-goog
>
Re: [PATCH 3/3] alloc_tag: avoid warnings when freeing non-compound "tail" pages
Posted by Suren Baghdasaryan 5 months ago 
On Thu, Sep 11, 2025 at 1:01 PM Shakeel Butt <shakeel.butt@linux.dev> wrote:
>
> On Tue, Sep 09, 2025 at 04:34:09PM -0700, Suren Baghdasaryan wrote:
> > When freeing "tail" pages of a non-compount high-order page, we properly
> > subtract the allocation tag counters, however later when these pages are
> > released, alloc_tag_sub() will issue warnings because tags for these pages
> > are NULL.
> > This issue was originally anticipated by Vlastimil in his review [1] and
> > then recently reported by David.
> > Prevent warnings by marking the tags empty.
> >
> > [1] https://lore.kernel.org/all/6db0f0c8-81cb-4d04-9560-ba73d63db4b8@suse.cz/
> >
> > Suggested-by: David Wang <00107082@163.com>
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > ---
> >  mm/page_alloc.c | 9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 1760346bbd24..d21a411e807e 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -5240,9 +5240,16 @@ static void ___free_pages(struct page *page, unsigned int order,
> >               __free_frozen_pages(page, order, fpi_flags);
> >       else if (!head) {
> >               pgalloc_tag_sub_pages(tag, (1 << order) - 1);
> > -             while (order-- > 0)
> > +             while (order-- > 0) {
> > +                     /*
> > +                      * The "tail" pages of this non-compound high-order
> > +                      * page will have no code tags, so to avoid warnings
> > +                      * mark them as empty.
> > +                      */
> > +                     clear_page_tag_ref(page + (1 << order));
>
> Do we need something similar for the release_pages() code path or is it
> happening already?

Pages released with release_pages() should have valid tags, so I
expect no warnings.

>
> >                       __free_frozen_pages(page + (1 << order), order,
> >                                           fpi_flags);
> > +             }
> >       }
> >  }
> >
> > --
> > 2.51.0.384.g4c02a37b29-goog
> >
>
Re: [PATCH 3/3] alloc_tag: avoid warnings when freeing non-compound "tail" pages
Posted by Shakeel Butt 5 months ago 
On Thu, Sep 11, 2025 at 01:12:11PM -0700, Suren Baghdasaryan wrote:
> On Thu, Sep 11, 2025 at 1:01 PM Shakeel Butt <shakeel.butt@linux.dev> wrote:
> >
> > On Tue, Sep 09, 2025 at 04:34:09PM -0700, Suren Baghdasaryan wrote:
> > > When freeing "tail" pages of a non-compount high-order page, we properly
> > > subtract the allocation tag counters, however later when these pages are
> > > released, alloc_tag_sub() will issue warnings because tags for these pages
> > > are NULL.
> > > This issue was originally anticipated by Vlastimil in his review [1] and
> > > then recently reported by David.
> > > Prevent warnings by marking the tags empty.
> > >
> > > [1] https://lore.kernel.org/all/6db0f0c8-81cb-4d04-9560-ba73d63db4b8@suse.cz/
> > >
> > > Suggested-by: David Wang <00107082@163.com>
> > > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > > ---
> > >  mm/page_alloc.c | 9 ++++++++-
> > >  1 file changed, 8 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index 1760346bbd24..d21a411e807e 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -5240,9 +5240,16 @@ static void ___free_pages(struct page *page, unsigned int order,
> > >               __free_frozen_pages(page, order, fpi_flags);
> > >       else if (!head) {
> > >               pgalloc_tag_sub_pages(tag, (1 << order) - 1);
> > > -             while (order-- > 0)
> > > +             while (order-- > 0) {
> > > +                     /*
> > > +                      * The "tail" pages of this non-compound high-order
> > > +                      * page will have no code tags, so to avoid warnings
> > > +                      * mark them as empty.
> > > +                      */
> > > +                     clear_page_tag_ref(page + (1 << order));
> >
> > Do we need something similar for the release_pages() code path or is it
> > happening already?
> 
> Pages released with release_pages() should have valid tags, so I
> expect no warnings.
> 

Oh so this is orthogonal to your first patch which is replacing
__free_page with release_pages(). This non-compound high-order page is
not an issue in the codepath vm_module_tags_populate(), correct?
Re: [PATCH 3/3] alloc_tag: avoid warnings when freeing non-compound "tail" pages
Posted by Suren Baghdasaryan 5 months ago 
On Thu, Sep 11, 2025 at 2:45 PM Shakeel Butt <shakeel.butt@linux.dev> wrote:
>
> On Thu, Sep 11, 2025 at 01:12:11PM -0700, Suren Baghdasaryan wrote:
> > On Thu, Sep 11, 2025 at 1:01 PM Shakeel Butt <shakeel.butt@linux.dev> wrote:
> > >
> > > On Tue, Sep 09, 2025 at 04:34:09PM -0700, Suren Baghdasaryan wrote:
> > > > When freeing "tail" pages of a non-compount high-order page, we properly
> > > > subtract the allocation tag counters, however later when these pages are
> > > > released, alloc_tag_sub() will issue warnings because tags for these pages
> > > > are NULL.
> > > > This issue was originally anticipated by Vlastimil in his review [1] and
> > > > then recently reported by David.
> > > > Prevent warnings by marking the tags empty.
> > > >
> > > > [1] https://lore.kernel.org/all/6db0f0c8-81cb-4d04-9560-ba73d63db4b8@suse.cz/
> > > >
> > > > Suggested-by: David Wang <00107082@163.com>
> > > > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > > > ---
> > > >  mm/page_alloc.c | 9 ++++++++-
> > > >  1 file changed, 8 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > > index 1760346bbd24..d21a411e807e 100644
> > > > --- a/mm/page_alloc.c
> > > > +++ b/mm/page_alloc.c
> > > > @@ -5240,9 +5240,16 @@ static void ___free_pages(struct page *page, unsigned int order,
> > > >               __free_frozen_pages(page, order, fpi_flags);
> > > >       else if (!head) {
> > > >               pgalloc_tag_sub_pages(tag, (1 << order) - 1);
> > > > -             while (order-- > 0)
> > > > +             while (order-- > 0) {
> > > > +                     /*
> > > > +                      * The "tail" pages of this non-compound high-order
> > > > +                      * page will have no code tags, so to avoid warnings
> > > > +                      * mark them as empty.
> > > > +                      */
> > > > +                     clear_page_tag_ref(page + (1 << order));
> > >
> > > Do we need something similar for the release_pages() code path or is it
> > > happening already?
> >
> > Pages released with release_pages() should have valid tags, so I
> > expect no warnings.
> >
>
> Oh so this is orthogonal to your first patch which is replacing
> __free_page with release_pages(). This non-compound high-order page is
> not an issue in the codepath vm_module_tags_populate(), correct?

Yes, these are independent fixes.

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