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

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Message-Id: <20121024181752.de011615.akpm@linux-foundation.org>
Date:	Wed, 24 Oct 2012 18:17:52 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Borislav Petkov <bp@...en8.de>,
	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 Thu, 25 Oct 2012 00:04:46 +0200 "Rafael J. Wysocki" <rjw@...k.pl> wrote:

> On Wednesday 24 of October 2012 14:13:03 Andrew Morton wrote:
> > On Wed, 24 Oct 2012 23:06:00 +0200
> > Borislav Petkov <bp@...en8.de> wrote:
> > 
> > > On Wed, Oct 24, 2012 at 01:48:36PM -0700, Andrew Morton wrote:
> > > > Well who knows. Could be that people's vm *does* suck. Or they have
> > > > some particularly peculiar worklosd or requirement[*]. Or their VM
> > > > *used* to suck, and the drop_caches is not really needed any more but
> > > > it's there in vendor-provided code and they can't practically prevent
> > > > it.
> > > 
> > > I have drop_caches in my suspend-to-disk script so that the hibernation
> > > image is kept at minimum and suspend times are as small as possible.
> > 
> > hm, that sounds smart.
> > 
> > > Would that be a valid use-case?
> > 
> > I'd say so, unless we change the kernel to do that internally.  We do
> > have the hibernation-specific shrink_all_memory() in the vmscan code. 
> > We didn't see fit to document _why_ that exists, but IIRC it's there to
> > create enough free memory for hibernation to be able to successfully
> > complete, but no more.
> 
> That's correct.

Well, my point was: how about the idea of reclaiming clean pagecache
(and inodes, dentries, etc) before hibernation so we read/write less
disk data?

Given that it's so easy to do from the hibernation script, I guess
there's not much point...


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