linux-kernel - Re: [PATCH v1] mm: remove total

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Date: Thu, 22 Feb 2024 18:16:26 +0100
From: David Hildenbrand <david@...hat.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v1] mm: remove total_mapcount()

On 22.02.24 18:13, Matthew Wilcox wrote:
> On Thu, Feb 22, 2024 at 05:09:43PM +0100, David Hildenbrand wrote:
>> We always get a head page, so we can just naturally interpret is as a folio
>> (similar to other code).
> 
> memfd seems rather confused about how to iterate over the page cache.
> Perhaps we could sort that out and then delete total_mapcount as a
> second patch?
> 
> I haven't tested this at all, but ...
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> 
> diff --git a/mm/memfd.c b/mm/memfd.c
> index d3a1ba4208c9..45e55b0e3cbe 100644
> --- a/mm/memfd.c
> +++ b/mm/memfd.c
> @@ -29,28 +29,29 @@
>   #define MEMFD_TAG_PINNED        PAGECACHE_TAG_TOWRITE
>   #define LAST_SCAN               4       /* about 150ms max */
>   
> +static bool memfd_extra_refs(struct folio *folio)
> +{
> +	return folio_ref_count(folio) - folio_mapcount(folio) !=
> +		folio_nr_pages(folio);
> +}

That is an obvious improvement I should have realized myself.

Let me play with that.

Thanks!

-- 
Cheers,

David / dhildenb