linux-kernel - Re: [PATCH 1/3] mm: kswapd: Stop high-order balancing when any suitable zone is balanced

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Date:	Wed, 01 Dec 2010 16:24:26 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Mel Gorman <mel@....ul.ie>, Simon Kirby <sim@...tway.ca>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] mm: kswapd: Stop high-order balancing when any
 suitable zone is balanced

On Wed, 2010-12-01 at 15:52 +0800, KOSAKI Motohiro wrote:
> > > > > we can't make
> > > > > perfect VM heuristics obviously, then we need to compare pros/cons.
> > > > if you don't care about small system, let's consider a NORMAL i386
> > > > system with 896m normal zone, and 896M*3 high zone. normal zone will
> > > > quickly exhaust by high order high zone allocation, leave a latter
> > > > allocation which does need normal zone fail.
> > > 
> > > Not happen. slab don't allocate from highmem and page cache allocation
> > > is always using order-0. When happen high order high zone allocation?
> > ok, thanks, I missed this. then how about a x86_64 box with 896M DMA32
> > and 896*3M NORMAL? some pci devices can only dma to DMA32 zone.
> 
> First, DMA32 is 4GB. Second, modern high end system don't use 32bit PCI
> device. Third, while we are thinking desktop users, 4GB is not small
> room. nowadays, typical desktop have only 2GB or 4GB memory.
DMA32 isn't 4G, because there is hole under 4G for PCI bars. I don't
think 32 bit PCI device is rare too. But anyway, if you insist this
isn't a big issue, I'm ok.

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