linux-kernel - Re: [PATCH] staging: zcache: fix possible sleep under lock

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Message-ID: <4E52CB88.1060401@linux.vnet.ibm.com>
Date:	Mon, 22 Aug 2011 16:35:04 -0500
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Dan Carpenter <error27@...il.com>
CC:	gregkh@...e.de, devel@...verdev.osuosl.org,
	dan.magenheimer@...cle.com, ascardo@...oscopio.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: zcache: fix possible sleep under lock

On 08/22/2011 04:10 PM, Dan Carpenter wrote:
> On Mon, Aug 22, 2011 at 02:49:45PM -0500, Seth Jennings wrote:
>> Actually, should this be GFP_ATOMIC or GFP_NOWAIT?
>>
> 
> GFP_ATOMIC is sort of a good default answer.
> 
> GFP_NOWAIT is normally used when you want to do something really
> fast and if the allocation fails, you don't want to wait for it.
> So if memory is short, and you drop a packet?  Who cares!  TCP has
> error handling built in.  Other than that, GFP_NOWAIT is used a lot
> in the core kernel.
> 
> You could be right that GFP_NOWAIT is fine here.  I don't know zcache
> well enough to say.  How bad is it if the allocation fails?
> 
> regards,
> dan carpenter

Meh... I think GFP_ATOMIC is fine.  If the allocation fails, then zcache
fails to initialise and the page cache and swaps just go down their normal
non-zache/frontswap/cleancache paths.  The only time there is a difference
between GFP_ATOMIC and GFP_NOWAIT, AFAIK, is if there are no non-emergency pages
left, which is unlikely to be the case.

Plus, I don't want to have to send out v3 of a one line patch :-/

Thanks,
Seth
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