Re: can a kmalloc be both GFP_ATOMIC and GFP_KERNEL at the sametime?

From: Andrew Morton
Date: Mon Apr 30 2007 - 03:13:29 EST

On Sat, 28 Apr 2007 09:40:39 -0400 (EDT) "Robert P. J. Day" <rpjday@xxxxxxxxxxxxxx> 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

The way to understand this is to look at the definitions:

#define GFP_NOIO (__GFP_WAIT)
#define GFP_NOFS (__GFP_WAIT | __GFP_IO)
#define GFP_KERNEL (__GFP_WAIT | __GFP_IO | __GFP_FS)

GFP_KERNEL: can sleep, can do IO, can enter filesystems

GFP_ATOMIC: cannot sleep, cannot do IO, cannot enter filesystems

Neither of them contains __GFP_DMA or __GFP_HIGHMEM, so both of them refer
to ZONE_NORMAL and any lower zones (ie: ZONE_DMA)
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