linux-kernel - Re: 2.6.35 Regression: Ages spent discarding blocks that weren't used!

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Message-ID: <4C59DA16.4020500@tuxonice.net>
Date:	Thu, 05 Aug 2010 07:22:30 +1000
From:	Nigel Cunningham <nigel@...onice.net>
To:	Mark Lord <kernel@...savvy.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: 2.6.35 Regression: Ages spent discarding blocks that weren't
 used!

Hi.

On 04/08/10 22:44, Mark Lord wrote:
> Looks to me like more and more things are using the block discard
> functionality, and as predicted it is slowing things down enormously.
>
> The problem is that we still only discard tiny bits (a single range
> still??)
> per TRIM command, rather than batching larger ranges and larger numbers
> of ranges into single TRIM commands.
>
> That's a very poor implementation, especially when things start enabling
> it by default. Eg. the swap code, mke2fs, etc..
>
> Ugh.

I was hoping for a nice quick and simple answer. Since I haven't got 
one, I'll try to find time to do a git bisect. I think I'll also look at 
the swap code more carefully and see if it's doing the sensible thing. I 
can't (at the moment) see the logic behind calling discard when 
allocating swap. At freeing time makes much more sense to me.

Regards,

Nigel
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