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Date: Fri, 6 Mar 2026 17:44:04 +0200
From: Mike Rapoport <rppt@kernel.org>
To: Pratyush Yadav <pratyush@kernel.org>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	stable@vger.kernel.org
Subject: Re: [PATCH 1/2] mm: memfd_luo: always make all folios uptodate
Message-ID: <aar2RJ3Bvs6Egmq8@kernel.org>
References: <20260223173931.2221759-1-pratyush@kernel.org>
 <20260223173931.2221759-2-pratyush@kernel.org>
 <aZ64ikDtz8tF_rFU@kernel.org>
 <2vxzqzpybqyd.fsf@kernel.org>
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In-Reply-To: <2vxzqzpybqyd.fsf@kernel.org>

On Thu, Mar 05, 2026 at 09:50:18AM +0100, Pratyush Yadav wrote:
> On Wed, Feb 25 2026, Mike Rapoport wrote:
> 
> > On Mon, Feb 23, 2026 at 06:39:28PM +0100, Pratyush Yadav wrote:
> [...]
> >> +
> >> +		/*
> >> +		 * If the folio is not uptodate, it was fallocated but never
> >> +		 * used. Saving this flag at prepare() doesn't work since it
> >> +		 * might change later when someone uses the folio.
> >> +		 *
> >> +		 * Since we have taken the performance penalty of allocating,
> >> +		 * zeroing, and pinning all the folios in the holes, take a bit
> >> +		 * more and zero all non-uptodate folios too.
> >> +		 *
> >> +		 * NOTE: For someone looking to improve preserve performance,
> >> +		 * this is a good place to look.
> >
> > I'd add a larger comment above memfd_luo_preserve_folios() that says that
> > it allocates, pins etc and fold the last two paragraphs of this comment
> > there.
> 
> How about this:
> 
> 	/*
> 	 * If the folio is not uptodate, it was fallocated but never
> 	 * used. Saving this flag at prepare() doesn't work since it
> 	 * might change later when the folio is used. Make it uptodate
> 	 * now to avoid this problem.
> 	 */
> 	if (!folio_test_uptodate(folio)) {
> 
> And the comment above memfd_pin_folios() gets this:
> 
> 	 * NOTE: For someone looking to improve preserve performance, this is a
> 	 * good place to look. Also look at the folio zeroing below.
 
Looks great to me

> [...]
> 
> -- 
> Regards,
> Pratyush Yadav

-- 
Sincerely yours,
Mike.