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Date: Tue, 26 Aug 2025 16:33:15 -0600
From: Keith Busch <kbusch@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Christoph Hellwig <hch@infradead.org>, Keith Busch <kbusch@meta.com>,
	linux-block@vger.kernel.org, linux-nvme@lists.infradead.org,
	axboe@kernel.dk, iommu@lists.linux.dev
Subject: Re: [PATCHv3 1/2] block: accumulate segment page gaps per bio
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 <aKxpSorluMXgOFEI@infradead.org>
 <aKxu83upEBhf5gT7@kbusch-mbp>
 <20250826130344.GA32739@lst.de>
 <aK27AhpcQOWADLO8@kbusch-mbp>
 <20250826135734.GA4532@lst.de>
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In-Reply-To: <20250826135734.GA4532@lst.de>

On Tue, Aug 26, 2025 at 03:57:34PM +0200, Christoph Hellwig wrote:
> On Tue, Aug 26, 2025 at 07:47:46AM -0600, Keith Busch wrote:
> > Currently, the virtual boundary is always compared to bv_offset, which
> > is a page offset. If the virtual boundary is larger than a page, then we
> > need something like "page_to_phys(bv.bv_page) + bv.bv_offset" every
> > place we need to check against the virt boundary.
> 
> bv_offset is only guaranteed to be a page offset if your use
> bio_for_each_segment(_all) or the low-level helpers implementing
> it and not bio_for_each_bvec(_all) where it can be much larger
> than PAGE_SIZE.

Yes, good point. So we'd have a folio offset when it's not a single
page, but I don't think we want to special case large folios for every
virt boundary check. It's looking like replace bvec's "page + offset"
with phys addrs, yeah?!