linux-kernel - Re: [PATCH 1/7] mm: introduce simple_malloc()/simple

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Date:	Sat, 15 Nov 2008 21:03:34 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>,
	Paul Menage <menage@...gle.com>,
	kamezawa.hiroyu@...fujitsu.com,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	"David S. Miller" <davem@...emloft.net>, Jan Kara <jack@...e.cz>,
	Jes Sorensen <jes@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/7] mm: introduce simple_malloc()/simple_free()

On Sat, 15 Nov 2008 20:52:29 -0800 Arjan van de Ven <arjan@...radead.org> wrote:

> On Sun, 16 Nov 2008 12:33:15 +0800
> Lai Jiangshan <laijs@...fujitsu.com> wrote:
> 
> > 
> > some subsystem needs vmalloc() when required memory is large.
> > but current kernel has not APIs for this requirement.
> > this patch introduces simple_malloc() and simple_free().
> 
> Hi
> 
> I kinda really don't like this approach. vmalloc() (and especially,
> vfree()) is a really expensive operation, and vmalloc()'d memory is
> also slower (due to tlb pressure).

And it can fragment, which effectively means a dead box.

> Realistically, people should try hard
> to use small datastructure instead....

Yup, it makes it easier for people to do something which we strongly
discourage.  The risk got worse with all these 64-bit machines with
vast amounts of virtual address space.  It makes it easier for people
to develop and "test" code which isn't reliable on smaller machines.

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