linux-kernel - Re: [PATCH] block: respect virtual boundary mask in bvecs

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Message-ID: <3c3dd9c2-4240-7bb5-c0ff-af6f2e479c31@suse.de>
Date:   Tue, 6 Nov 2018 13:34:03 +0100
From:   Johannes Thumshirn <jthumshirn@...e.de>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Jens Axboe <axboe@...com>,
        Linux Block Layer Mailinglist <linux-block@...r.kernel.org>,
        Hannes Reinecke <hare@...e.de>,
        Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>,
        Jan Kara <jack@...e.cz>, Sagi Grimberg <sagi@...mberg.me>
Subject: Re: [PATCH] block: respect virtual boundary mask in bvecs

On 05/11/2018 13:01, Ming Lei wrote:
> If you mean the real huge page, this patch shouldn't have made a difference
> because bio_vec->bv_offset is in [0, PAGE_SIZE), and iSer sets virt
> boundary as 4K - 1.
> 
> However, things will change after multipage bvec is introduced.


Hi Ming,

I've received a blktrace from our customer showing the issue [1].

In this example trace they've submitted (contiguous) 64K I/Os and
without this patch, they're seeing a lot of splits as indicated by the
trace.

With the patch applied the I/O is directly issued to the LLDD without
the splits.

[1] http://beta.suse.com/private/jthumshirn/blktrace.txt

Byte,
	Johannes
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Johannes Thumshirn                                        SUSE Labs
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