Re: can a kmalloc be both GFP_ATOMIC and GFP_KERNEL at the sametime?
From: Robert P. J. Day
Date: Mon Apr 30 2007 - 05:53:39 EST
On Mon, 30 Apr 2007, Jan Engelhardt wrote:
> On Apr 30 2007 04:46, Robert P. J. Day 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?
> #define GFP_ATOMIC (__GFP_HIGH)
> #define GFP_KERNEL (__GFP_WAIT | __GFP_IO | __GFP_FS)
> So combining GFP_ATOMIC with GFP_KERNEL gives you
> "allow io, allow fs, allow waiting, and use emergency pools when it's getting
> which to me looks like a valid, but probably unwanted combination.
... snip ...
at this point, maybe i'll just leave this in the hands of those who
know far more about it than i do. but, while we're here, are there
any *other* combinations that wouldn't make any sense? might as well
check for those in my cleanup script as well.
p.s. as a suggestion that borders on overkill, one could always add a
configuration debugging option that, when set, compiles code into
kmalloc() that does a sanity check on its type flag arguments.
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry
Waterloo, Ontario, CANADA
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