linux-kernel - Re: [PATCH v1 3/6] fs/proc/task_mmu: properly detect PM_MMAP

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Date: Mon, 10 Jun 2024 06:51:09 +0200
From: Oscar Salvador <osalvador@...e.de>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v1 3/6] fs/proc/task_mmu: properly detect
 PM_MMAP_EXCLUSIVE per page of PMD-mapped THPs

On Fri, Jun 07, 2024 at 02:23:54PM +0200, David Hildenbrand wrote:
> We added PM_MMAP_EXCLUSIVE in 2015 via commit 77bb499bb60f ("pagemap: add
> mmap-exclusive bit for marking pages mapped only here"), when THPs could
> not be partially mapped and page_mapcount() returned something
> that was true for all pages of the THP.
> 
> In 2016, we added support for partially mapping THPs via
> commit 53f9263baba6 ("mm: rework mapcount accounting to enable 4k mapping
> of THPs") but missed to determine PM_MMAP_EXCLUSIVE as well per page.
> 
> Checking page_mapcount() on the head page does not tell the whole story.
> 
> We should check each individual page. In a future without per-page
> mapcounts it will be different, but we'll change that to be consistent
> with PTE-mapped THPs once we deal with that.
> 
> Fixes: 53f9263baba6 ("mm: rework mapcount accounting to enable 4k mapping of THPs")
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>

Reviewed-by: Oscar Salvador <osalvador@...e.de>

-- 
Oscar Salvador
SUSE Labs