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Date: Tue, 4 Aug 2026 19:42:23 +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 v14 05/21] fsverity: improve flushing performance of
 fsverity_fill_zerohash
Message-ID: <20260804174223.GB14046@lst.de>
References: <20260803200820.393203-1-aalbersh@kernel.org> <20260803200820.393203-6-aalbersh@kernel.org>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Mon, Aug 03, 2026 at 10:07:55PM +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) on the HIGHMEM
> systems. Open code folio mapping and flushing to copy all digests at
> once.

This looks correct, although to me optimizing for this feels like
premature optimizations not worth the ugly code unless we have numbers
to justify it.

If Eric wants it:

Reviewed-by: Christoph Hellwig <hch@lst.de>

> +		if (folio_test_partial_kmap(folio) &&
> +		    off > PAGE_SIZE - offset_in_page(offset))
> +			off = PAGE_SIZE - offset_in_page(offset);
> +		for (; to < (vaddr + off); to += vi->tree_params.digest_size)

Style nitpick: no need for braces when comparing with simple
integer arithmetics like this.

> +	for (off = offset; off < (offset + len);

Same here.