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

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Message-ID: <49224FBC.2000702@cn.fujitsu.com>
Date:	Tue, 18 Nov 2008 13:16:44 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	balbir@...ux.vnet.ibm.com, Arjan van de Ven <arjan@...radead.org>,
	Dave Airlie <airlied@...il.com>,
	David Miller <davem@...emloft.net>, menage@...gle.com,
	jens.axboe@...cle.com, jack@...e.cz, jes@....com,
	linux-kernel@...r.kernel.org, dada1@...mosbay.com,
	Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: [PATCH 1/7] mm: introduce simple_malloc()/simple_free()

Nick Piggin wrote:
> On Monday 17 November 2008 18:13, Andrew Morton wrote:
>> On Mon, 17 Nov 2008 15:43:59 +0900 "KOSAKI Motohiro" 
> <kosaki.motohiro@...fujitsu.com> wrote:
>>>>>> (I'll rename simple_malloc/simple_free to kvmalloc/kvfree)
>>>>> I would prefer to find a way to say that one cannot select gfp_mask
>>>>> with this API.
>>>> I think gfp_mask must be passed explicitly.
>>> Agreed.
>> It would only make sense if __vmalloc() can be called in atomic contexts.
>>
>> __vmalloc() cannot be called from irq contexts due to it taking
>> non-irq-safe spinlocks.
>>
>> __vmalloc() kinda looks like it could be called from non-irq atomic
>> contexts with GFP_ATOMIC, but I think it lies.  For example,
>> pud_alloc_one/pmd_alloc_one/etc use hard-wired GFP_KERNEL.
> 
> vmalloc/vfree / vmap/vunmap I think could now be made to be usable even
> in irq context, I think. Freeing up vmalloc space with global tlb flush
> can't be done from interrupt context, but now with the lazy unmapping,
> you only have to mark the area as freed (and possibly kick off a thread
> to do the actual unmapping).
> 
> I didn't actually add that, because yes it would increase overheads a
> bit, and I would still prefer to wait for a real nice problem it solves
> before adding such a capability...
> 
> 
>> In which case this new allocation function can only be called from
>> contexts where GFP_KERNEL can be used, hence we don't need to pass that
>> in - it would be misleading to do so.
>>
>> In fact it's not immediately clear why __vmalloc() takes a gfp_t
>> argument either?
> 
> Possibly a bugcheck for !GFP_WAIT || !GFP_FS || !GFP_IO, or a might_sleep()
> or something would be a good idea to add...
> 
> 
> 

Thanks.
Now, new patch for it is: http://lkml.org/lkml/2008/11/17/137

Lai.


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