linux-kernel - Re: [PATCH 5/6] PM/Hibernate: Do not release preallocated memory unnecessarily (rev. 2)

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Date:	Thu, 14 May 2009 19:52:20 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nigel Cunningham <nigel@...onice.net>,
	David Rientjes <rientjes@...gle.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 5/6] PM/Hibernate: Do not release preallocated memory unnecessarily (rev. 2)

On Thursday 14 May 2009, Pavel Machek wrote:
> Hi!
> 
> > Since the hibernation code is now going to use allocations of memory
> > to make enough room for the image, it can also use the page frames
> > allocated at this stage as image page frames.  The low-level
> > hibernation code needs to be rearranged for this purpose, but it
> > allows us to avoid freeing a great number of pages and allocating
> > these same pages once again later, so it generally is worth doing.
> > 
> > [rev. 2: Take highmem into account correctly.]
> 
> I don't get it. What is advantage of this patch? It makes the code
> more complex... Is it supposed to be faster?

Yes, in some test cases it is reported to be faster (along with [4/6],
actually).

Besides, we'd like to get rid of shrink_all_memory() eventually and it is a
step in this direction.

Thanks,
Rafael
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