linux-kernel - Re: [PATCH 1/1] mm/madvise: enhance lazyfreeing with mTHP in madvise

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Date: Tue, 27 Feb 2024 09:49:59 +1300
From: Barry Song <21cnbao@...il.com>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Lance Yang <ioworker0@...il.com>, David Hildenbrand <david@...hat.com>, akpm@...ux-foundation.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhocko@...e.com, 
	minchan@...nel.org, peterx@...hat.com, shy828301@...il.com, 
	songmuchun@...edance.com, wangkefeng.wang@...wei.com, zokeefe@...gle.com, 
	fengwei.yin@...el.com
Subject: Re: [PATCH 1/1] mm/madvise: enhance lazyfreeing with mTHP in madvise_free

On Tue, Feb 27, 2024 at 2:04 AM Ryan Roberts <ryan.roberts@....com> wrote:
>
> On 26/02/2024 08:55, Lance Yang wrote:
> > Hey David,
> >
> > Thanks for your suggestion!
> >
> > On Mon, Feb 26, 2024 at 4:41 PM David Hildenbrand <david@...hatcom> wrote:
> >>
> > [...]
> >>> On Mon, Feb 26, 2024 at 12:00 PM Barry Song <21cnbao@...il.com> wrote:
> >>> [...]
> >>>> On Mon, Feb 26, 2024 at 1:33 AM Lance Yang <ioworker0@...il.com> wrote:
> >>> [...]
> > [...]
> >>> +static inline bool pte_range_cont_mapped(pte_t *pte, unsigned long nr)
> >>> +{
> >>> +     pte_t pte_val;
> >>> +     unsigned long pfn = pte_pfn(pte);
> >>> +     for (int i = 0; i < nr; i++) {
> >>> +             pte_val = ptep_get(pte + i);
> >>> +             if (pte_none(pte_val) || pte_pfn(pte_val) != (pfn + i))
> >>> +                     return false;
> >>> +     }
> >>> +     return true;
> >>> +}
> >>
> >> I dislike the "cont mapped" terminology.
> >>
> >> Maybe folio_pte_batch() does what you want?
> >
> > folio_pte_batch() is a good choice. Appreciate it!
>
> Agreed, folio_pte_batch() is likely to be widely useful for this change and
> others, so suggest exporting it from memory.c and reusing as is if possible.

I actually missed folio_pte_batch() in cont-pte series and re-invented
a function
to check if a large folio is entirely mapped in MADV_PAGEOUT[1]. exporting
folio_pte_batch() will also benefit that case. The problem space is same.

[1] https://lore.kernel.org/linux-mm/20240118111036.72641-7-21cnbao@gmail.com/

>
> >
> > Best,
> > Lance
> >
> >>
> >> --
> >> Cheers,
> >>
> >> David / dhildenb

Thanks
Barry