From: Yang Shi <shy828301@gmail.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <songmuchun@bytedance.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linux MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] mm: pvmw: check possible huge PMD map by transhuge_vma_suitable()
Date: Thu, 12 May 2022 20:51:26 -0700 [thread overview]
Message-ID: <CAHbLzkrALZm43JOCwc38pRzcMwX3u0FNqwUEZS3pGi=3eT_V9Q@mail.gmail.com> (raw)
In-Reply-To: <Yn3Q7KIb3FcAPW9j@casper.infradead.org>
On Thu, May 12, 2022 at 8:30 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Thu, May 12, 2022 at 10:45:51AM -0700, Yang Shi wrote:
> > IIUC PVMW checks if the vma is possibly huge PMD mapped by
> > transparent_hugepage_active() and "pvmw->nr_pages >= HPAGE_PMD_NR".
> >
> > Actually pvmw->nr_pages is returned by compound_nr() or
> > folio_nr_pages(), so the page should be THP as long as "pvmw->nr_pages
> > >= HPAGE_PMD_NR". And it is guaranteed THP is allocated for valid VMA
> > in the first place. But it may be not PMD mapped if the VMA is file
> > VMA and it is not properly aligned. The transhuge_vma_suitable()
> > is used to do such check, so replace transparent_hugepage_active() to
> > it, which is too heavy and overkilling.
> >
> > Fixes: 2aff7a4755be ("mm: Convert page_vma_mapped_walk to work on PFNs")
>
> I think Fixes is a bit much. There's no bug being fixed here. This is
> just an optimisation. Is it an important optimisation? We could put a
Yeah, it is just an optimization, will remove the fix tag.
I'm trying to do some cleanup for all the transhuge_page_* checks
suggested by Vlastimil. I should be able to kill
transparent_hugepage_active() by replacing it with
transhuge_vma_suitable() here.
> bool into page_vma_mapped_walk() so we only have to ask the page whether
> it's PMD-mappable once per walk rather than for each VMA.
The page may be PMD-mappable for one VMA, but not for the other VMA.
>
next prev parent reply other threads:[~2022-05-13 3:51 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-12 17:45 [PATCH 1/2] mm: rmap: use the correct parameter name for DEFINE_PAGE_VMA_WALK Yang Shi
2022-05-12 17:45 ` [PATCH 2/2] mm: pvmw: check possible huge PMD map by transhuge_vma_suitable() Yang Shi
2022-05-12 23:39 ` Andrew Morton
2022-05-13 0:39 ` Yang Shi
2022-05-13 1:41 ` kernel test robot
2022-05-13 3:30 ` Matthew Wilcox
2022-05-13 3:51 ` Yang Shi [this message]
2022-05-13 2:16 ` [PATCH 1/2] mm: rmap: use the correct parameter name for DEFINE_PAGE_VMA_WALK Matthew Wilcox
2022-05-13 2:42 ` Muchun Song
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