linux-kernel - Re: [PATCH] block: blk-merge: fast-clone bio when splitting rw bios

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Date:	Thu, 17 Sep 2015 09:19:11 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Ming Lei <ming.lei@...onical.com>, linux-kernel@...r.kernel.org
Cc:	Christoph Hellwig <hch@...radead.org>,
	Kent Overstreet <kent.overstreet@...il.com>,
	Ming Lin <ming.l@....samsung.com>,
	Dongsu Park <dpark@...teo.net>
Subject: Re: [PATCH] block: blk-merge: fast-clone bio when splitting rw bios

On 09/17/2015 09:13 AM, Ming Lei wrote:
> biovecs has become immutable since v3.13, so it isn't necessary
> to allocate biovecs for the new cloned bios, then we can save
> one extra biovecs allocation/copy, and the allocation is often
> not fixed-length and a bit more expensive.
>
> For example, if the 'max_sectors_kb' of null blk's queue is set
> as 16(32 sectors) via sysfs just for making more splits, this patch
> can increase throught about ~70% in the sequential read test over
> null_blk(direct io, bs: 1M).

I'd be curious how this compares to before we did the splitting, not 
exceeding the limits through bio_add_page() instead?

-- 
Jens Axboe

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