linux-kernel - Re: [PATCH 2/2] Make is_mem_section_removable more conformable with offlining code

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Date:	Fri, 3 Sep 2010 13:01:14 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Hiroyuki Kamezawa <kamezawa.hiroyuki@...il.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Kleen, Andi" <andi.kleen@...el.com>,
	Haicheng Li <haicheng.li@...ux.intel.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mel Gorman <mel@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/2] Make is_mem_section_removable more conformable
 with offlining code

On Fri 03-09-10 19:05:20, KAMEZAWA Hiroyuki wrote:
> On Fri, 3 Sep 2010 11:50:49 +0200
> Michal Hocko <mhocko@...e.cz> wrote:
> 
> > On Fri 03-09-10 18:13:27, KAMEZAWA Hiroyuki wrote:
> > > On Fri, 3 Sep 2010 10:25:58 +0200
> > > Michal Hocko <mhocko@...e.cz> wrote:
> > > 
> > > > On Fri 03-09-10 12:14:52, KAMEZAWA Hiroyuki wrote:
> > > > [...]
> > [...]
> > > > Cannot ZONE_MOVABLE contain different MIGRATE_types?
> > > > 
> > > never.
> > 
> > Then I am terribly missing something. Zone contains free lists for
> > different MIGRATE_TYPES, doesn't it? Pages allocated from those free
> > lists keep the migration type of the list, right?
> > 
> > ZONE_MOVABLE just says whether it makes sense to move pages in that zone
> > at all, right?
> > 
> 
>  ZONE_MOVABLE means "it only contains MOVABLE pages."
>  So, we can ignore migrate-type.

Ahh. OK, it seems that I have to look over movable related code once
again. Maybe I just got confused from my experience when ZONE_MOVABLE
zone contained MIGRATE_RESERVE pages but now I can see that this is OK
and doesn't have anything to do with other migrate types.

Anyway, thank you for clarification.

[...]

> > > > Isn't this a problem? The function is triggered from userspace by sysfs
> > > > (0444 file) and holds the lock for pageblock_nr_pages. So someone can
> > > > simply read the file and block the zone->lock preventing/delaying
> > > > allocations for the rest of the system.
> > > > 
> > > But we need to take this. Maybe no panic you'll see even if no-lock.
> > 
> > Yes, I think that this can only lead to a false possitive in sysfs
> > interface. Isolating code holds the lock.
> > 
> 
> ok, let's go step by step.
> 
> I'm ok that your new patch to be merged. I'll post some clean up and small
> bugfix (not related to your patch), later.
> (I'll be very busy in this weekend, sorry.)

OK, no problem, we are not in hurry ;)

> 
> 
> Thanks,
> -Kame
> 

Thanks!

-- 
Michal Hocko
L3 team 
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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