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Re: [PATCH 2/4] Add a __GFP_SLABMEMCG flag [message #46757 is a reply to message #46751] Sat, 09 June 2012 00:56 Go to previous messageGo to previous message
James Bottomley is currently offline  James Bottomley
Messages: 17
Registered: May 2006
Junior Member
On Fri, 2012-06-08 at 14:31 -0500, Christoph Lameter wrote:
> On Fri, 8 Jun 2012, Glauber Costa wrote:
>
> > */
> > #define __GFP_NOTRACK_FALSE_POSITIVE (__GFP_NOTRACK)
> >
> > -#define __GFP_BITS_SHIFT 25 /* Room for N __GFP_FOO bits */
> > +#define __GFP_BITS_SHIFT 26 /* Room for N __GFP_FOO bits */
> > #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
>
> Please make this conditional on CONFIG_MEMCG or so. The bit can be useful
> in particular on 32 bit architectures.

I really don't think that's at all a good idea. It's asking for trouble
when we don't spot we have a flag overlap. It also means that we're
trusting the reuser to know that their use case can never clash with
CONFIG_MEMGC and I can't think of any configuration where this is
possible currently.

I think making the flag define of __GFP_SLABMEMCG conditional might be a
reasonable idea so we get a compile failure if anyone tries to use it
when !CONFIG_MEMCG.

James

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