> From: Matthew Wilcox [mailto:willy@xxxxxxxxxxxxx] > Sent: Friday, May 11, 2018 9:26 PM> > On Fri, May 11, 2018 at 03:24:34AM +0000, Huaisheng HS1 Ye wrote: > > > From: owner-linux-mm@xxxxxxxxx [mailto:owner-linux-mm@xxxxxxxxx] On Behalf Of > Matthew > > > Wilcox > > > On Fri, May 11, 2018 at 12:10:25AM +0800, Huaisheng Ye wrote: > > > > -#define __GFP_DMA ((__force gfp_t)___GFP_DMA) > > > > -#define __GFP_HIGHMEM ((__force gfp_t)___GFP_HIGHMEM) > > > > -#define __GFP_DMA32 ((__force gfp_t)___GFP_DMA32) > > > > +#define __GFP_DMA ((__force gfp_t)OPT_ZONE_DMA ^ ZONE_NORMAL) > > > > +#define __GFP_HIGHMEM ((__force gfp_t)ZONE_MOVABLE ^ ZONE_NORMAL) > > > > +#define __GFP_DMA32 ((__force gfp_t)OPT_ZONE_DMA32 ^ ZONE_NORMAL) > > > > > > No, you've made gfp_zone even more complex than it already is. > > > If you can't use OPT_ZONE_HIGHMEM here, then this is a waste of time. > > > > > Dear Matthew, > > > > The reason why I don't use OPT_ZONE_HIGHMEM for __GFP_HIGHMEM directly is that, > for x86_64 platform there is no CONFIG_HIGHMEM, so OPT_ZONE_HIGHMEM shall always be > equal to ZONE_NORMAL. > > Right. On 64-bit platforms, if somebody asks for HIGHMEM, they should > get NORMAL pages. > > > For gfp_zone it is impossible to distinguish the meaning of lowest 3 bits in flags. > How can gfp_zone to understand it comes from OPT_ZONE_HIGHMEM or ZONE_NORMAL? > > And the most pained thing is that, if __GFP_HIGHMEM with movable flag enabled, it > means that ZONE_MOVABLE shall be returned. > > That is different from ZONE_DMA, ZONE_DMA32 and ZONE_NORMAL. > > The point of this exercise is to actually encode the zone number in > the bottom bits of the GFP flags instead of something which has to be > interpreted into a zone number. When somebody sets __GFP_MOVABLE, they > should also be setting ZONE_MOVABLE: > > -#define __GFP_MOVABLE ((__force gfp_t)___GFP_MOVABLE) /* ZONE_MOVABLE allowed */ > +#define __GFP_MOVABLE ((__force gfp_t)(___GFP_MOVABLE | (ZONE_MOVABLE ^ ZONE_NORMAL))) > I am afraid we couldn't do that, because __GFP_MOVABLE would be used potentially with other __GFPs like __GFP_DMA and __GFP_DMA32. Let's go back to the previous example. We assume ZONE_DMA equals to 0, and ZONE_DMA32 equals to 1. After encoding with ZONE_NORMAL (which equals to 2), we could get that. #define __GFP_DMA ((__force gfp_t)OPT_ZONE_DMA ^ ZONE_NORMAL) #define __GFP_DMA32 ((__force gfp_t)OPT_ZONE_DMA32 ^ ZONE_NORMAL) __GPF_DMA = 0b 0010 __GPF_DMA32 = 0b 0011 We assume ZONE_MOVABLE equals to 3, #define __GFP_MOVABLE ((__force gfp_t)(___GFP_MOVABLE | (ZONE_MOVABLE ^ ZONE_NORMAL))) __GFP_MOVABLE = 0b 1001 If we OR'ing __GFP_MOVABLE and either __GFP_DMA or __GFP_DMA32, we could get same result as '0b 1011'. This is unacceptable, because inline function gfp_zone couldn't distinguish that is a request of ZONE_DMA or ZONE_DMA32 from parameter flags. Once more, I think if we want to encode ZONE_MOVABLE to __GFP_MOVABLE, then the operation of __GFP_MOVABLE OR'ing with any other __GFP* would have risk. Sincerely, Huaisheng Ye > One thing that does need to change is: > > -#define GFP_HIGHUSER_MOVABLE (GFP_HIGHUSER | __GFP_MOVABLE) > +#define GFP_HIGHUSER_MOVABLE (GFP_USER | __GFP_MOVABLE) > > otherwise we'll be OR'ing ZONE_MOVABLE and ZONE_HIGHMEM together. > > > I was thinking... > > Whether it is possible to use other judgement condition to decide OPT_ZONE_HIGHMEM > or ZONE_MOVABLE shall be returned from gfp_zone. > > > > Sincerely, > > Huaisheng Ye > > > > > > > > static inline enum zone_type gfp_zone(gfp_t flags) > > > > { > > > > enum zone_type z; > > > > - int bit = (__force int) (flags & GFP_ZONEMASK); > > > > + z = ((__force unsigned int)flags & ___GFP_ZONE_MASK) ^ ZONE_NORMAL; > > > > + > > > > + if (z > OPT_ZONE_HIGHMEM) > > > > + z = OPT_ZONE_HIGHMEM + > > > > + !!((__force unsigned int)flags & ___GFP_MOVABLE); > > > > > > > > - z = (GFP_ZONE_TABLE >> (bit * GFP_ZONES_SHIFT)) & > > > > - ((1 << GFP_ZONES_SHIFT) - 1); > > > > - VM_BUG_ON((GFP_ZONE_BAD >> bit) & 1); > > > > + VM_BUG_ON(z > ZONE_MOVABLE); > > > > return z; > > > > } > >
