linux-kernel - GFP_NOWAIT and GFP

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Message-ID: <f22d86810909290425s46406fe5ib00bcfc9673f70df@mail.gmail.com>
Date:	Tue, 29 Sep 2009 16:55:24 +0530
From:	"Leonidas ." <leonidas137@...il.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: GFP_NOWAIT and GFP_NOMEMALLOC

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.

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*/

Is there any flag which fetches memory from GFP_KERNEL pool with a
guarantee that
it will not sleep?

Does GFP_NOWAIT | GFP_KERNEL guarantee that?

Is ( GFP_NOWAIT | GFP_KERNEL ) == ( GFP_ATOMIC - dont access emergency pools)?

I am a bit confused about GFP_NOWAIT and GFP_NOMEMALLOC, any pointers will be
helpful.

-Leo.
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