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Date: Mon, 6 Nov 2023 08:02:55 -0700
From: Keith Busch <kbusch@kernel.org>
To: Kanchan Joshi <joshi.k@samsung.com>
Cc: Keith Busch <kbusch@meta.com>, linux-block@vger.kernel.org,
	linux-nvme@lists.infradead.org, io-uring@vger.kernel.org,
	axboe@kernel.dk, hch@lst.de, martin.petersen@oracle.com
Subject: Re: [PATCHv2 1/4] block: bio-integrity: directly map user buffers
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References: <20231027181929.2589937-1-kbusch@meta.com>
 <CGME20231027182010epcas5p36bcf271f93f821055206b2e04b3019a6@epcas5p3.samsung.com>
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In-Reply-To: <40ac82f5-ce1b-6f49-3609-1aff496ae241@samsung.com>

On Mon, Nov 06, 2023 at 11:18:03AM +0530, Kanchan Joshi wrote:
> On 10/27/2023 11:49 PM, Keith Busch wrote:
> > +	for (i = 0; i < nr_vecs; i = j) {
> > +		size_t size = min_t(size_t, bytes, PAGE_SIZE - offs);
> > +		struct folio *folio = page_folio(pages[i]);
> > +
> > +		bytes -= size;
> > +		for (j = i + 1; j < nr_vecs; j++) {
> > +			size_t next = min_t(size_t, PAGE_SIZE, bytes);
> > +
> > +			if (page_folio(pages[j]) != folio ||
> > +			    pages[j] != pages[j - 1] + 1)
> > +				break;
> > +			unpin_user_page(pages[j]);
> 
> Is this unpin correct here?

Should be. The pages are bound to the folio, so this doesn't really
unpin the user page. It just drops a reference, and the folio holds the
final reference to the contiguous pages, which is released on
completion. You can find the same idea in io_uring/rscs.c,
io_sqe_buffer_register().