linux-kernel - Re: [PATCH 2/2 v2] UBI: Block: Add blk-mq support

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Date:	Wed, 14 Jan 2015 00:36:48 +0100
From:	Richard Weinberger <richard@....at>
To:	Jens Axboe <axboe@...com>, Christoph Hellwig <hch@...radead.org>
CC:	dedekind1@...il.com, dwmw2@...radead.org,
	computersforpeace@...il.com, linux-mtd@...ts.infradead.org,
	linux-kernel@...r.kernel.org, tom.leiming@...il.com
Subject: Re: [PATCH 2/2 v2] UBI: Block: Add blk-mq support



Am 14.01.2015 um 00:30 schrieb Jens Axboe:
>> If I understand you correctly it can happen that blk_rq_bytes() returns
>> more bytes than blk_rq_map_sg() allocated, right?
> 
> No, the number of bytes will be the same, no magic is involved :-)

Good to know. :)

> But lets say the initial request has 4 bios, with each 2 pages, for a
> total of 8 segments. Lets further assume that the pages in each bio are
> contiguous, so that blk_rq_map_sg() will map this to 4 sg elements, each
> 2xpages long.
> 
> Now, this may already be handled just fine, and you don't need to
> update/store the actual sg count. I just looked at the source, and I'm
> assuming it'll do the right thing (ubi_read_sg() will bump the active sg
> element, when that size has been consumed), but I don't have
> ubi_read_sg() in my tree to verify.

Currently the sg count is hard coded to UBI_MAX_SG_COUNT.

I'm sorry, I forgot to CC you and hch to this patch:
https://lkml.org/lkml/2015/1/10/204

Thanks,
//richard

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