linux-kernel - Re: 4.4-final: 28 bioset threads on small notebook

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Message-ID: <CACVXFVNMMhR-uOSYvV+VLrSFtmQZUmoQBSAwKFcXcSvB_HUO-A@mail.gmail.com>
Date:	Tue, 23 Feb 2016 10:55:48 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Kent Overstreet <kent.overstreet@...il.com>
Cc:	Ming Lin-SSI <ming.l@....samsung.com>, Pavel Machek <pavel@....cz>,
	Mike Snitzer <snitzer@...hat.com>,
	kernel list <linux-kernel@...r.kernel.org>,
	"axboe@...com" <axboe@...com>, "hch@....de" <hch@....de>,
	"neilb@...e.de" <neilb@...e.de>,
	"martin.petersen@...cle.com" <martin.petersen@...cle.com>,
	"dpark@...teo.net" <dpark@...teo.net>,
	"dm-devel@...hat.com" <dm-devel@...hat.com>,
	"agk@...hat.com" <agk@...hat.com>,
	"jkosina@...e.cz" <jkosina@...e.cz>,
	"geoff@...radead.org" <geoff@...radead.org>,
	"jim@...n.com" <jim@...n.com>,
	"pjk1939@...ux.vnet.ibm.com" <pjk1939@...ux.vnet.ibm.com>,
	"minchan@...nel.org" <minchan@...nel.org>,
	"ngupta@...are.org" <ngupta@...are.org>,
	"oleg.drokin@...el.com" <oleg.drokin@...el.com>,
	"andreas.dilger@...el.com" <andreas.dilger@...el.com>
Subject: Re: 4.4-final: 28 bioset threads on small notebook

On Tue, Feb 23, 2016 at 6:58 AM, Kent Overstreet
<kent.overstreet@...il.com> wrote:
> On Sun, Feb 21, 2016 at 05:40:59PM +0800, Ming Lei wrote:
>> On Sun, Feb 21, 2016 at 2:43 PM, Ming Lin-SSI <ming.l@....samsung.com> wrote:
>> >>-----Original Message-----
>> >
>> > So it's almost already "per request_queue"
>>
>> Yes, that is because of the following line:
>>
>> q->bio_split = bioset_create(BIO_POOL_SIZE, 0);
>>
>> in blk_alloc_queue_node().
>>
>> Looks like this bio_set doesn't need to be per-request_queue, and
>> now it is only used for fast-cloning bio for splitting, and one global
>> split bio_set should be enough.
>
> It does have to be per request queue for stacking block devices (which includes
> loopback).

In commit df2cb6daa4(block: Avoid deadlocks with bio allocation by
stacking drivers), deadlock in this situation has been avoided already.
Or are there other issues with global bio_set? I appreciate if you may
explain it a bit if there are.

Thanks,
Ming Lei