linux-kernel - Re: [PATCH v1 2/2] fs/proc/task_mmu: convert smaps_hugetlb

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Message-ID: <Zh_BKoUNK0uKJF8r@localhost.localdomain>
Date: Wed, 17 Apr 2024 14:31:38 +0200
From: Oscar Salvador <osalvador@...e.de>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Muchun Song <muchun.song@...ux.dev>
Subject: Re: [PATCH v1 2/2] fs/proc/task_mmu: convert smaps_hugetlb_range()
 to work on folios

On Wed, Apr 17, 2024 at 02:18:10PM +0200, David Hildenbrand wrote:
> On 17.04.24 14:09, Oscar Salvador wrote:
> > On Wed, Apr 17, 2024 at 11:23:13AM +0200, David Hildenbrand wrote:
> > > Let's get rid of another page_mapcount() check and simply use
> > > folio_likely_mapped_shared(), which is precise for hugetlb folios.
> > > 
> > > While at it, use huge_ptep_get() + pte_page() instead of ptep_get() +
> > > vm_normal_page(), just like we do in pagemap_hugetlb_range().
> > 
> > That is fine because vm_normal_page() tries to be clever about  mappings which
> > hugetlb does not support, right?
> 
> Right, using vm_normal_page() is even completely bogus. Usually (but not
> always) we have PMDs/PUDs and not PTEs for mapping hugetlb pages -- where
> vm_normal_folio_pmd() would be the right thing to do.
> 
> That's also the reason why hugetlb.c has not a single user of
> vm_normal_page() and friends ... it doesn't apply to hugetlb, but likely
> also isn't currently harmful to use it.

I guess not because we skip the special handling, but I agree that
replacing it is the right thing to do.
Thanks for explaining!
 

-- 
Oscar Salvador
SUSE Labs