Re: [PATCH v1 3/6] fs/proc/task_mmu: properly detect PM_MMAP_EXCLUSIVE per page of PMD-mapped THPs

[Oscar Salvador]

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@xxxxxxxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>

Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>

-- 
Oscar Salvador
SUSE Labs