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 9:56 AM Suren Baghdasaryan <surenb@google.com> wrote:
>
> 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!

v2 posted at [1]

As a reminder for Andrew, the patchset [1] should replace the older
patch [2] currently present in mm-unstable and mm-hotfixes-unstable.

[1] https://lore.kernel.org/all/20240717181239.2510054-2-surenb@google.com/
[2] ac5ca7954e4e ("alloc_tag: export memory allocation profiling
symbols used by modules")

Thanks,
Suren.

>
> >
> > > ---
> > >  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;
> >