Re: [PATCH 2/2] alloc_tag: outline and export {get|put}_page_tag_ref() used by modules

[Suren Baghdasaryan <surenb@google.com>]

On Wed, Jul 17, 2024 at 2:30 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> On 7/17/24 3:16 AM, Suren Baghdasaryan wrote:
> > Outline and export get_page_tag_ref() and put_page_tag_ref() so that
> > modules can use them without exporting page_ext_get() and page_ext_put().
> >
> > Fixes: dcfe378c81f7 ("lib: introduce support for page allocation tagging")
> > Reported-by: kernel test robot <lkp@intel.com>
> > Closes: https://lore.kernel.org/oe-kbuild-all/202407080044.DWMC9N9I-lkp@intel.com/
> > Suggested-by: Christoph Hellwig <hch@infradead.org>
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
>
> Better than exporting page_ext but still seems like suboptimal level to me.
> You have various inline functions that use get/put_page_tag_ref and now will
> call into them both. IMHO outlining those (and leaving only the static key
> check inline) is the better way.
>
> As for the report that triggered this, AFAICS it was due to
> free_reserved_page() so it could be enough to only outline that memalloc
> profiling part there and leave the rest as that seems to be used only from
> core code and no modules.

Doh! I didn't realize that's the only place these functions are used
directly but looks like you are right. Outlining free_reserved_page()
is definitely a much better solution with less performance impact.
I'll post a replacement patch shortly.
Thanks Vlastimil!

>
> > ---
> >  include/linux/pgalloc_tag.h | 23 +++--------------------
> >  lib/alloc_tag.c             | 23 +++++++++++++++++++++++
> >  2 files changed, 26 insertions(+), 20 deletions(-)
> >
> > diff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h
> > index 9cacadbd61f8..3c6ab717bd57 100644
> > --- a/include/linux/pgalloc_tag.h
> > +++ b/include/linux/pgalloc_tag.h
> > @@ -13,6 +13,9 @@
> >
> >  extern struct page_ext_operations page_alloc_tagging_ops;
> >
> > +union codetag_ref *get_page_tag_ref(struct page *page);
> > +void put_page_tag_ref(union codetag_ref *ref);
> > +
> >  static inline union codetag_ref *codetag_ref_from_page_ext(struct page_ext *page_ext)
> >  {
> >       return (void *)page_ext + page_alloc_tagging_ops.offset;
> > @@ -23,26 +26,6 @@ static inline struct page_ext *page_ext_from_codetag_ref(union codetag_ref *ref)
> >       return (void *)ref - page_alloc_tagging_ops.offset;
> >  }
> >
> > -/* Should be called only if mem_alloc_profiling_enabled() */
> > -static inline union codetag_ref *get_page_tag_ref(struct page *page)
> > -{
> > -     if (page) {
> > -             struct page_ext *page_ext = page_ext_get(page);
> > -
> > -             if (page_ext)
> > -                     return codetag_ref_from_page_ext(page_ext);
> > -     }
> > -     return NULL;
> > -}
> > -
> > -static inline void put_page_tag_ref(union codetag_ref *ref)
> > -{
> > -     if (WARN_ON(!ref))
> > -             return;
> > -
> > -     page_ext_put(page_ext_from_codetag_ref(ref));
> > -}
> > -
> >  static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,
> >                                  unsigned int nr)
> >  {
> > diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> > index 832f79a32b3e..5271cc070901 100644
> > --- a/lib/alloc_tag.c
> > +++ b/lib/alloc_tag.c
> > @@ -4,6 +4,7 @@
> >  #include <linux/gfp.h>
> >  #include <linux/module.h>
> >  #include <linux/page_ext.h>
> > +#include <linux/pgalloc_tag.h>
> >  #include <linux/proc_fs.h>
> >  #include <linux/seq_buf.h>
> >  #include <linux/seq_file.h>
> > @@ -22,6 +23,28 @@ struct allocinfo_private {
> >       bool print_header;
> >  };
> >
> > +/* Should be called only if mem_alloc_profiling_enabled() */
> > +union codetag_ref *get_page_tag_ref(struct page *page)
> > +{
> > +     if (page) {
> > +             struct page_ext *page_ext = page_ext_get(page);
> > +
> > +             if (page_ext)
> > +                     return codetag_ref_from_page_ext(page_ext);
> > +     }
> > +     return NULL;
> > +}
> > +EXPORT_SYMBOL_GPL(get_page_tag_ref);
> > +
> > +void put_page_tag_ref(union codetag_ref *ref)
> > +{
> > +     if (WARN_ON(!ref))
> > +             return;
> > +
> > +     page_ext_put(page_ext_from_codetag_ref(ref));
> > +}
> > +EXPORT_SYMBOL_GPL(put_page_tag_ref);
> > +
> >  static void *allocinfo_start(struct seq_file *m, loff_t *pos)
> >  {
> >       struct allocinfo_private *priv;
>