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.
> 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;
> }
> From: [email protected] [mailto:[email protected]] 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.
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.
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;
> > }
On Fri, May 11, 2018 at 03:24:34AM +0000, Huaisheng HS1 Ye wrote:
> > From: [email protected] [mailto:[email protected]] 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.
> 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;
> > > }
>
> From: Matthew Wilcox [mailto:[email protected]]
> Sent: Friday, May 11, 2018 9:26 PM>
> On Fri, May 11, 2018 at 03:24:34AM +0000, Huaisheng HS1 Ye wrote:
> > > From: [email protected] [mailto:[email protected]] 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;
> > > > }
> >
On Sat, May 12, 2018 at 11:35:00AM +0000, Huaisheng HS1 Ye wrote:
> > 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.
That's not a combination that makes much sense. I know it's permitted today
(and it has the effect of being a no-op), but when you think about it, it
doesn't actually make any sense.
> From: Matthew Wilcox [mailto:[email protected]]
> Sent: Saturday, May 12, 2018 10:23 PM>
> On Sat, May 12, 2018 at 11:35:00AM +0000, Huaisheng HS1 Ye wrote:
> > > 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.
>
> That's not a combination that makes much sense. I know it's permitted today
> (and it has the effect of being a no-op), but when you think about it, it
> doesn't actually make any sense.
Yes, you are right.
After checking almost all references of __GFP_MOVABLE and other __GFP_* flags, perhaps I was far to get excessive pursuit of logical correctness.
For those nonsense combinations, I should ignore them.
Current GFP_ZONE_TABLE can ensure all logical correctness. That makes me want to pursue same effect.
Next, I will revise the patch according to your advice, then try to get overall testing result as far as possible.
There are many combinations because of a lot of conditions in file system and drivers. Hope I could test all things related to the lower 4 bits of gfp.
Sincerely,
Huaisheng Ye
> From: Matthew Wilcox [mailto:[email protected]]
> Sent: Friday, May 11, 2018 9:26 PM
> On Fri, May 11, 2018 at 03:24:34AM +0000, Huaisheng HS1 Ye wrote:
> > > From: [email protected] [mailto:[email protected]] 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;
> > > > }
> >