linux-kernel - Re: [PATCH] add some drop_caches documentation and info messsge

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Date:	Wed, 31 Oct 2012 18:31:54 +0100
From:	Pavel Machek <pavel@....cz>
To:	Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] add some drop_caches documentation and info messsge

On Mon 2012-10-29 10:58:19, Borislav Petkov wrote:
> On Mon, Oct 29, 2012 at 09:59:59AM +0100, Jiri Kosina wrote:
> > You might or might not want to do that. Dropping caches around suspend
> > makes the hibernation process itself faster, but the realtime response
> > of the applications afterwards is worse, as everything touched by user
> > has to be paged in again.

Also note that page-in is slower than  reading hibernation image,
because it is not compressed, and involves seeking.

> Right, do you know of a real use-case where people hibernate, then
> resume and still care about applications response time right afterwards?

Hmm? When I resume from hibernate, I want to use my
machine. *Everyone* cares about resume time afterwards. You move your
mouse, and you don't want to wait for X to be paged-in.

> Besides, once everything is swapped back in, perf. is back to normal,
> i.e. like before suspending.

Kernel will not normally swap anything in automatically. Some people
do swapoff -a; swapon -a to work around that. (And yes, maybe some
automatic-swap-in-when-there's-plenty-of-RAM would be useful.).
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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