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Date: Fri, 24 Jul 2026 15:13:09 +0200
From: Christoph Hellwig <hch@lst.de>
To: Andrey Albershteyn <aalbersh@kernel.org>
Cc: linux-xfs@vger.kernel.org, fsverity@lists.linux.dev,
	linux-fsdevel@vger.kernel.org, ebiggers@kernel.org, hch@lst.de,
	linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net,
	linux-btrfs@vger.kernel.org, djwong@kernel.org
Subject: Re: [PATCH v13 05/23] fsverity: improve flushing performance of
 fsverity_fill_zerohash
Message-ID: <20260724131309.GA27878@lst.de>
References: <20260721184346.416657-1-aalbersh@kernel.org> <20260721184346.416657-6-aalbersh@kernel.org>
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On Tue, Jul 21, 2026 at 08:40:42PM +0200, Andrey Albershteyn wrote:
> The current version calls flush_dcache_folio(), in memcpy_to_folio(), to
> flush whole folio on every digest (which is 128 for 4k). Open code folio
> mapping and flushing to copy all digests at once.

What is the point of this?  flush_dcache_folio is a no-op on sane
architectures, and this should not be a performance path, so
avoiding all the kmap logic does seem benefitial.  Or at least only
opencode it for !highmem to avoid the worst part.