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Date: Wed, 5 Jul 2017 19:26:16 +0200
From: Christoph Hellwig <hch@lst.de>
To: Damien Le Moal <damien.lemoal@wdc.com>
Cc: linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v2] block: Fix __blkdev_issue_zeroout loop
Message-ID: <20170705172616.GA5417@lst.de>
References: <20170704082702.15727-1-damien.lemoal@wdc.com>
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On Tue, Jul 04, 2017 at 05:27:02PM +0900, Damien Le Moal wrote:
> The BIO issuing loop in __blkdev_issue_zeroout() is allocating BIOs
> with a maximum number of bvec (pages) equal to
> 
> min(nr_sects, (sector_t)BIO_MAX_PAGES)
> 
> This works since the BIO will always be limited to the absolute maximum
> number of pages but this is ineficient as too many bvec entries may be
> requested since different units (number of sectors vs number of pages)
> are used in the min() operation. Fix this by correctly using the same
> unit (number of pages), making sure that this number is at least 1 for
> cases where the number of sectors is less that the number of sectors in
> a page.
> 
> Also remove a trailing space after the bit shift in the internal loop
> min() call.

Can you move the nr sectors calculation into a helper and add some
comments?