linux-kernel - Re: [PATCH] umem: fix up unplugging.

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Message-ID: <CAAV8rnKuYoyNjhpPSLk4XJiwG7XYL11pUfdNx1Jn9mNji-9+Mw@mail.gmail.com>
Date:	Thu, 5 Apr 2012 21:09:16 -0700
From:	Tao Guo <glorioustao@...il.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, neilb@...e.de, axboe@...ionio.com
Subject: Re: [PATCH] umem: fix up unplugging.

On Thu, Apr 5, 2012 at 4:51 PM, Jens Axboe <axboe@...nel.dk> wrote:
> On 2012-04-04 17:58, Tao Guo wrote:
>> On Wed, Apr 4, 2012 at 4:18 PM, Jens Axboe <axboe@...nel.dk> wrote:
>>> On 2012-04-04 16:20, Tao Guo wrote:
>>>> Hi Andrew,
>>>>
>>>> Thanks for your reply.
>>>>
>>>> Yes, without this patch the umem driver just doesn't work.
>>>> It is a bug introduced by commit 7eaceaccab5f40bbfda044629a6298616aeaed50.
>>>> In that patch, Jens removed the whole mm_unplug_device() function,
>>>> which used to be
>>>> the trigger to make umem start to work.
>>>
>>> Hmm indeed, that's isn't terribly useful. Why aren't we just calling
>>> activate_card() on addition of a bio?
>>>
>> It is the original design idea, the umem driver also wants to do batch
>> IO the same as
>> hard disk drive to fully utilize the IO bandwidth.
>
> Sure, just wondering whether the benefits have been tested. But yes, it
> certainly makes sense.
>
> Your patch looks buggy, though. What if the card is currently plugged on
> another tasks plug list? You seem to assume that it can only be plugged
> once.
No, it will register in its own plug callback list successfully, so
the unplug functions
will be called separately(twice the same).
-Tao
>
> --
> Jens Axboe
>
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