linux-kernel - Re: can a kmalloc be both GFP_ATOMIC and GFP

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Message-Id: <20070430100225.353e3030.akpm@linux-foundation.org>
Date:	Mon, 30 Apr 2007 10:02:25 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Robert P. J. Day" <rpjday@...dspring.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: can a kmalloc be both GFP_ATOMIC and GFP_KERNEL at the same
 time?

On Mon, 30 Apr 2007 04:46:54 -0400 (EDT) "Robert P. J. Day" <rpjday@...dspring.com> wrote:

> On Mon, 30 Apr 2007, Andrew Morton wrote:
> 
> > On Sat, 28 Apr 2007 09:40:39 -0400 (EDT) "Robert P. J. Day" <rpjday@...dspring.com> wrote:
> >
> > >
> > >   i'd always assumed that the type flags of GFP_ATOMIC and GFP_KERNEL
> > > were mutually exclusive when it came to calling kmalloc(), at least
> > > based on everything i'd read.  so i'm not sure how to interpret the
> > > following:
> > >
> > > drivers/scsi/aic7xxx_old.c:  aic_dev = kmalloc(sizeof(struct aic_dev_data), GFP_ATOMIC | GFP_KERNEL);
> > > drivers/message/i2o/device.c:   resblk = kmalloc(buflen + 8, GFP_KERNEL | GFP_ATOMIC);
> > >
> > >   clarification?
> >
> > GFP_ATOMIC implies that the memory comes from the zones which
> > GFP_KERNEL also uses.  So the above usage of GFP_KERNEL is redundant
> > and should be removed.
> 
> hang on ... based on an email i just got, is that reference to
> GFP_KERNEL "redundant" or "conflicting"?  big difference there.  and
> is the proper fix to remove "GFP_KERNEL" in both cases?
> 

umm, yeah, oops.  GFP_KERNEL|GFP_ATOMIC is not a redundant combination. 
It's GFP_KERNEL plus "is able to access emergency pools".  We'd normally
represent that as GFP_KERNEL|__GFP_HIGH.

However it's questionable whether that was the intent in those two drivers.
`git-blame' might tell.

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