linux-kernel - Re: GFP_NOWAIT and GFP

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Message-ID: <20091004185627.GA1378@ucw.cz>
Date:	Sun, 4 Oct 2009 20:56:27 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Leonidas ." <leonidas137@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: GFP_NOWAIT and GFP_NOMEMALLOC

On Tue 2009-09-29 16:55:24, Leonidas . wrote:
> Hi list,
> 
> I am new here, I have googled/binged enough before posting this message,
> in case of redundancy please point me to appropriate links/resources etc.
> 
> I want to kmalloc memory while holding spinlocks in process context, here I
> can't use GFP_KERNEL flag since it can sleep. Using GFP_ATOMIC guarantees
> that allocation will succeed by allocating from emergency pools if needed.
> But I dont think, I need to use emergency pool and I want to limit my memory
> consumption to ZONE_NORMAL without sleeping, my module is ready to handle
> the allocation failure if any.

Umm. Either preallocate, or use gfp_atomic. It should be ok.

> Something like,
> 
> ptr =  kmalloc(..., GFP_KERNEL | GFP_DONT_SLEEP );
> 
> if( !ptr ) {
> 
>  /*GFP_KERNEL failed, Use GFP_ATOMIC pool*/
>  ptr =  kmalloc(..., GFP_ATOMIC );
> 
> }
> /*Go ahead and do stuff*/

That's pretty stupid, no? Just alloc GFP_ATOMIC directly... oh and
check return values...
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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