Re: [PATCH] Revert "mm: remove __GFP_NO_KSWAPD"

Glauber Costa
2012-11-21T08:30:30Z

On 11/21/2012 12:18 AM, Andrew Morton wrote:
> On Tue, 20 Nov 2012 13:18:19 +0400
> Glauber Costa <glommer@parallels.com> wrote:
>
>> On 11/12/2012 03:37 PM, Mel Gorman wrote:
>>> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
>>> index 02c1c971..d0a7967 100644
>>> --- a/include/linux/gfp.h
>>> +++ b/include/linux/gfp.h
>>> @@ -31,6 +31,7 @@ struct vm_area_struct;
>>> #define ___GFP_THISNODE 0x40000u
>>> #define ___GFP_RECLAIMABLE 0x80000u
>>> #define ___GFP_NOTRACK 0x200000u
>>> +#define ___GFP_NO_KSWAPD 0x400000u
>>> #define ___GFP_OTHER_NODE 0x800000u
>>> #define ___GFP_WRITE 0x1000000u
>>
>> Keep in mind that this bit has been reused in -mm.
>> If this patch needs to be reverted, we'll need to first change
>> the definition of __GFP_KMEMCG (and __GFP_BITS_SHIFT as a result), or it
>> would break things.
>
> I presently have
>
> /* Plain integer GFP bitmasks. Do not use this directly. */
> #define ___GFP_DMA 0x01u
> #define ___GFP_HIGHMEM 0x02u
> #define ___GFP_DMA32 0x04u
> #define ___GFP_MOVABLE 0x08u
> #define ___GFP_WAIT 0x10u
> #define ___GFP_HIGH 0x20u
> #define ___GFP_IO 0x40u
> #define ___GFP_FS 0x80u
> #define ___GFP_COLD 0x100u
> #define ___GFP_NOWARN 0x200u
> #define ___GFP_REPEAT 0x400u
> #define ___GFP_NOFAIL 0x800u
> #define ___GFP_NORETRY 0x1000u
> #define ___GFP_MEMALLOC 0x2000u
> #define ___GFP_COMP 0x4000u
> #define ___GFP_ZERO 0x8000u
> #define ___GFP_NOMEMALLOC 0x10000u
> #define ___GFP_HARDWALL 0x20000u
> #define ___GFP_THISNODE 0x40000u
> #define ___GFP_RECLAIMABLE 0x80000u
> #define ___GFP_KMEMCG 0x100000u
> #define ___GFP_NOTRACK 0x200000u
> #define ___GFP_NO_KSWAPD 0x400000u
> #define ___GFP_OTHER_NODE 0x800000u
> #define ___GFP_WRITE 0x1000000u
>
> and
>

Humm, I didn't realize there were also another free space at 0x100000u.
This seems fine.

> #define __GFP_BITS_SHIFT 25 /* Room for N __GFP_FOO bits */
> #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
>
> Which I think is OK?
Yes, if we haven't increased the size of the flag-space, no need to
change it.

>
> I'd forgotten about __GFP_BITS_SHIFT. Should we do this?
>
> --- a/include/linux/gfp.h~a
> +++ a/include/linux/gfp.h
> @@ -35,6 +35,7 @@ struct vm_area_struct;
> #define ___GFP_NO_KSWAPD 0x400000u
> #define ___GFP_OTHER_NODE 0x800000u
> #define ___GFP_WRITE 0x1000000u
> +/* If the above are modified, __GFP_BITS_SHIFT may need updating */
>
This is a very helpful comment.