linux-kernel - Re: [RFC 06/11] khugepaged: generalize alloc_charge

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Message-ID: <CAA1CXcDKKyG4QA_M91UqHGBru2GdubgCx2m1PUpFu3ftonS4zw@mail.gmail.com>
Date: Fri, 10 Jan 2025 12:41:54 -0700
From: Nico Pache <npache@...hat.com>
To: Dev Jain <dev.jain@....com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, ryan.roberts@....com, 
	anshuman.khandual@....com, catalin.marinas@....com, cl@...two.org, 
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	srivatsa@...il.mit.edu, haowenchao22@...il.com, hughd@...gle.com, 
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	21cnbao@...il.com, willy@...radead.org, kirill.shutemov@...ux.intel.com, 
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	sunnanyong@...wei.com, usamaarif642@...il.com, audra@...hat.com, 
	akpm@...ux-foundation.org
Subject: Re: [RFC 06/11] khugepaged: generalize alloc_charge_folio for mTHP support

On Thu, Jan 9, 2025 at 11:24 PM Dev Jain <dev.jain@....com> wrote:
>
>
>
> On 09/01/25 5:01 am, Nico Pache wrote:
> > alloc_charge_folio allocates the new folio for the khugepaged collapse.
> > Generalize the order of the folio allocations to support future mTHP
> > collapsing.
> >
> > No functional changes in this patch.
> >
> > Signed-off-by: Nico Pache <npache@...hat.com>
> > ---
> >   mm/khugepaged.c | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index e2e6ca9265ab..6daf3a943a1a 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -1070,14 +1070,14 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm,
> >   }
> >
> >   static int alloc_charge_folio(struct folio **foliop, struct mm_struct *mm,
> > -                           struct collapse_control *cc)
> > +                           struct collapse_control *cc, int order)
> >   {
> >       gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() :
> >                    GFP_TRANSHUGE);
> >       int node = khugepaged_find_target_node(cc);
> >       struct folio *folio;
> >
> > -     folio = __folio_alloc(gfp, HPAGE_PMD_ORDER, node, &cc->alloc_nmask);
> > +     folio = __folio_alloc(gfp, order, node, &cc->alloc_nmask);
> >       if (!folio) {
> >               *foliop = NULL;
> >               count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
> > @@ -1121,7 +1121,7 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
> >        */
> >       mmap_read_unlock(mm);
> >
> > -     result = alloc_charge_folio(&folio, mm, cc);
> > +     result = alloc_charge_folio(&folio, mm, cc, HPAGE_PMD_ORDER);
> >       if (result != SCAN_SUCCEED)
> >               goto out_nolock;
> >
> > @@ -1834,7 +1834,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
> >       VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
> >       VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
> >
> > -     result = alloc_charge_folio(&new_folio, mm, cc);
> > +     result = alloc_charge_folio(&new_folio, mm, cc, HPAGE_PMD_ORDER);
> >       if (result != SCAN_SUCCEED)
> >               goto out;
> >
>
> I guess we will need stat updation like I did in my patch.

Yeah stats were on my TODO list, as well as cleaning up some of the
tracing. Those will be done before the PATCH posting.

>