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From: Wols Lists <antlists@youngman.org.uk>
To: "Guilherme G. Piccoli" <guilherme@gpiccoli.net>,
	Song Liu <liu.song.a23@gmail.com>
Cc: "Guilherme G. Piccoli" <gpiccoli@canonical.com>,
	linux-block@vger.kernel.org,
	linux-raid <linux-raid@vger.kernel.org>,
	dm-devel@redhat.com, axboe@kernel.dk,
	Gavin Guo <gavin.guo@canonical.com>,
	Jay Vosburgh <jay.vosburgh@canonical.com>,
	kernel@gpiccoli.net, Ming Lei <ming.lei@redhat.com>,
	Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	stable@vger.kernel.org
Subject: Re: [PATCH 2/2] md/raid0: Do not bypass blocking queue entered for raid0 bios
Date: Wed, 8 May 2019 17:52:59 +0100	[thread overview]
Message-ID: <5CD3096B.4030302@youngman.org.uk> (raw)
In-Reply-To: <0ad36b2f-ec36-6930-b587-da0526613567@gpiccoli.net>

On 08/05/19 15:52, Guilherme G. Piccoli wrote:
> Hi, I understand your concern. But all other raid levels contains
> failure-event mechanisms. For example, in all my tests with raid5 or
> raid1, it first complained the device was removed, then it failed in
> super_written() when no other available device was present.
> On the other hand, raid0 does "blind-writes": it just selects the device
> in which that bio should be written (given the stripe math) and change
> the bio's device, sending it back via generic_make_request(). It's
> dummy, but not in a bad way, but rather for performance reasons. It has
> no "intelligence" for failures, as all other raid levels.
> 
> That said, we could fix md.c for all raid levels, but I personally think
> it's a bazooka shot, only raid0 shows consistently this issue.
> 
The academic in me says we should push that error handling into
generic_make_request() or some raid function in md.c that deals with
those problems. Sounds like there's a fair bit of duplicate
functionality that could be re-factored out.
>>
>> Academic purity versus engineering practicality :-)
> 
> Heheh you have good points here! Thanks for the input =)
> Cheers,
> 
Doesn't help when there's not an architect to design an overall "grand
scheme", but my usual way of working is to design top down academically,
and then ask myself "what do I need" before implementing bottom-up.
Hopefully with a load of documentation saying "I haven't done this
because I don't need it, but this is where it goes".

Cheers,
Wol


  reply	other threads:[~2019-05-08 16:53 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-30 22:37 [PATCH 1/2] block: Fix a NULL pointer dereference in generic_make_request() Guilherme G. Piccoli
2019-04-30 22:37 ` [PATCH 2/2] md/raid0: Do not bypass blocking queue entered for raid0 bios Guilherme G. Piccoli
2019-05-06 16:50   ` Song Liu
2019-05-06 18:48     ` Guilherme G. Piccoli
2019-05-06 21:07       ` Song Liu
2019-05-07 21:51         ` Guilherme G. Piccoli
2019-05-08  9:29         ` Wols Lists
2019-05-08 14:52           ` Guilherme G. Piccoli
2019-05-08 16:52             ` Wols Lists [this message]
2019-05-17 16:19               ` Guilherme G. Piccoli
2019-05-20 16:23                 ` Song Liu
2019-05-20 19:25                   ` Guilherme Piccoli
2019-04-30 22:55 ` [PATCH 1/2] block: Fix a NULL pointer dereference in generic_make_request() Bart Van Assche
2019-05-17  3:33 ` Eric Ren
2019-05-17 16:17   ` Guilherme G. Piccoli
2019-05-20  2:43     ` Eric Ren
2019-05-17 22:04 ` Ming Lei
2019-05-23 17:23 Song Liu
2019-05-23 17:23 ` [PATCH 2/2] md/raid0: Do not bypass blocking queue entered for raid0 bios Song Liu
2019-06-12 12:40   ` Guilherme Piccoli
2019-06-12 12:48     ` Greg KH
2019-06-12 16:38       ` Guilherme G. Piccoli
2019-06-12 16:37   ` Guilherme G. Piccoli
2019-06-12 16:49     ` Greg KH
2019-06-12 18:07       ` Guilherme Piccoli
2019-06-12 18:36         ` Greg KH
2019-06-12 18:43         ` Sasha Levin
2019-06-12 18:48           ` Guilherme Piccoli

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