makedumpfile memory usage grows with system memory size

[HATAYAMA Daisuke]

From: Atsushi Kumagai <kumagai-atsushi at mxc.nes.nec.co.jp>
Subject: Re: makedumpfile memory usage grows with system memory size
Date: Wed, 16 May 2012 17:02:30 +0900

> On Mon, 14 May 2012 14:44:28 +0900 (JST)
> HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com> wrote:

>> Anyway, I think it better to add _mapcount information to VMCOREINFO
>> on upstream as soon as possible.
> 
> I think it's better way to use _mapcount. 
> But we don't certainly decide to use _mapcount and even if we decide to use it,
> we still have problems to use it.
> For example, the upstream kernel(v3.4-rc7) has _mapcount in union, we need
> a information to judge whether the found data is _mapcount or not. 
> So, more investigation is needed and I think it's too early to send the request
> to upstream kernel.

A quick look into the other part of the union---inuse, objects,
froze---to which _mapcount belongs, they appears to be used in SLUB
allocator. The page with PG_slab appears to use the other part to
_mapcount. This means that to decide whether to use _mapcount, it's
necessary to first investigate how SLUB allocator works.

> 
> I plan to finish working to reduce memory consumption by the end of June, 
> and I will continue to discuss performance issues.
> Therefore, the request will be delayed until July or August.
> 

I'll wait for your patch on memory consumption and feedback to
it. I'll also look into possibility of filtering free memory in
constant space on recent kernels.

Thanks.
HATAYAMA, Daisuke