Re: [PATCH v7 mm-new 03/10] mm: thp: decouple THP allocation between swap and page fault paths

[Yafang Shao <laoar.shao@gmail.com>]

On Thu, Sep 11, 2025 at 10:56 PM Lorenzo Stoakes
<lorenzo.stoakes@oracle.com> wrote:
>
> On Wed, Sep 10, 2025 at 10:44:40AM +0800, Yafang Shao wrote:
> > The new BPF capability enables finer-grained THP policy decisions by
> > introducing separate handling for swap faults versus normal page faults.
> >
> > As highlighted by Barry:
> >
> >   We’ve observed that swapping in large folios can lead to more
> >   swap thrashing for some workloads- e.g. kernel build. Consequently,
> >   some workloads might prefer swapping in smaller folios than those
> >   allocated by alloc_anon_folio().
> >
> > While prtcl() could potentially be extended to leverage this new policy,
> > doing so would require modifications to the uAPI.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
>
> Other than nits, these seems fine, so:
>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
>
> > Cc: Barry Song <21cnbao@gmail.com>
> > ---
> >  include/linux/huge_mm.h | 3 ++-
> >  mm/huge_memory.c        | 2 +-
> >  mm/memory.c             | 2 +-
> >  3 files changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index f72a5fd04e4f..b9742453806f 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -97,9 +97,10 @@ extern struct kobj_attribute thpsize_shmem_enabled_attr;
> >
> >  enum tva_type {
> >       TVA_SMAPS,              /* Exposing "THPeligible:" in smaps. */
> > -     TVA_PAGEFAULT,          /* Serving a page fault. */
> > +     TVA_PAGEFAULT,          /* Serving a non-swap page fault. */
> >       TVA_KHUGEPAGED,         /* Khugepaged collapse. */
> >       TVA_FORCED_COLLAPSE,    /* Forced collapse (e.g. MADV_COLLAPSE). */
> > +     TVA_SWAP,               /* Serving a swap */
>
> Serving a swap what? :) I think TVA_SWAP_PAGEFAULT would be better here right?
> And 'serving a swap page fault'.

will change it. Thanks for your suggestion.

-- 
Regards
Yafang