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From: Andrew Morton <akpm@linux-foundation.org>
To: Yang Shi <shy828301@gmail.com>
Cc: willy@infradead.org, songmuchun@bytedance.com,
	linux-mm@kvack.org, 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 16:39:02 -0700	[thread overview]
Message-ID: <20220512163902.5e128f6dd5dd6e44afa53259@linux-foundation.org> (raw)
In-Reply-To: <20220512174551.81279-2-shy828301@gmail.com>

On Thu, 12 May 2022 10:45:51 -0700 Yang Shi <shy828301@gmail.com> 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.
> 
> ...
>
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -237,13 +237,14 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>  			spin_unlock(pvmw->ptl);
>  			pvmw->ptl = NULL;
>  		} else if (!pmd_present(pmde)) {
> +			unsigned long haddr = pvmw->address & HPAGE_PMD_MASK;

This hits

	#define HPAGE_PMD_MASK ({ BUILD_BUG(); 0; })

when CONFIG_TRANSPARENT_HUGEPAGE=n (x86_64 allnoconfig).


  reply	other threads:[~2022-05-12 23:39 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 [this message]
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
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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