> 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))) > > 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. Dear Matthew, After thinking it over and over, I am afraid there is something needs to be discussed here. You know current X86_64 config file of kernel doesn't enable CONFIG_HIGHMEM, that is to say from this below, #define __GFP_HIGHMEM ((__force gfp_t)OPT_ZONE_HIGHMEM ^ ZONE_NORMAL) __GFP_HIGHMEM should equal to 0b0000, same as the value of ZONE_NORMAL gets encoded. If we define __GFP_MOVABLE like this, #define __GFP_MOVABLE ((__force gfp_t)(___GFP_MOVABLE | (ZONE_MOVABLE ^ ZONE_NORMAL))) Just like your introduced before, with this modification when somebody sets __GFP_MOVABLE, they should also be setting ZONE_MOVABLE. That brings us a problem, current mm (GFP_ZONE_TABLE) treats __GFP_MOVABLE as ZONE_NORMAL with movable policy, if without __GFP_HIGHMEM. The mm shall allocate a page or pages from migrate movable list of ZONE_NORMAL's freelist. So that conflicts with this modification. And I have checked current kernel, some of function directly set parameter gfp like this. For example, in fs/ext4/extents.c __read_extent_tree_block, bh = sb_getblk_gfp(inode->i_sb, pblk, __GFP_MOVABLE | GFP_NOFS); for these situations, I think only modify GFP_HIGHUSER_MOVABLE is not enough. I am preparing a workaround to solve this in the V2 patch. Later I will upload it to email loop. Sincerely, Huaisheng Ye > > 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; > > > > } > >
