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

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Date:	Sun, 16 Nov 2008 07:08:37 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Lai Jiangshan <laijs@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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()

Arjan van de Ven a écrit :
> On Sun, 16 Nov 2008 13:35:03 +0800
> Lai Jiangshan <laijs@...fujitsu.com> wrote:
> 
>> vmalloc() is not good for performance and increasing fragment.
>> but vmalloc() is need for some subsystems' alternative malloc,
>> like cgroup's tasks file and other subsystems(about 20 subsystems).
> 
> actually what you are pointing out is that these areas need improvement
> to not need such huge blocks of memory... but only a series of smaller
> blocks instead.
> 


Just zap vmalloc()/vfree() then ?

More seriously, vmalloc()/vfree() were designed partly to make people life easier,
not to be *the* premium interface to manage kernel memory

Some parts of the kernel cannot afford the cost of vmalloc()/vfree(), so people
must think and design complex algos.

I personnaly like this cleanup too. For example bnx2 driver actually uses vmalloc() while
a kmalloc() should be OK for bnx2_alloc_rx_mem()

# grep bnx2 /proc/vmallocinfo
0xf8260000-0xf8274000   81920 bnx2_init_board+0x104/0xae0 phys=f6000000 ioremap
0xf8280000-0xf8294000   81920 bnx2_init_board+0x104/0xae0 phys=fa000000 ioremap
0xf82c1000-0xf82c3000    8192 bnx2_alloc_rx_mem+0x33/0x310 pages=1 vmalloc
0xf82d9000-0xf82db000    8192 bnx2_alloc_rx_mem+0x33/0x310 pages=1 vmalloc

I have two comments :

1) Names should be not "simple" : That is misleading. "convenient" maybe, or "slow"...

2) Since vmalloc()/vfree() is potentially a very expensive operation, we should make
   slow_malloc()/slow_free() or whatever name is chosen, uninlined. No need to try to save
   3 or 4 cpu cycles. This will save icache at least.


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