Re: [PATCH v5 1/1] mm: enumerate all gfp flags

[Suren Baghdasaryan]

On Sat, Feb 24, 2024 at 7:03 AM Christophe JAILLET
<christophe.jaillet@xxxxxxxxxx> wrote:
>
> Le 24/02/2024 à 02:58, Suren Baghdasaryan a écrit :
> > Introduce GFP bits enumeration to let compiler track the number of used
> > bits (which depends on the config options) instead of hardcoding them.
> > That simplifies __GFP_BITS_SHIFT calculation.
> >
> > Suggested-by: Petr Tesařík <petr@xxxxxxxxxxx>
> > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > Reviewed-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
> > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> > ---
> > Changes from v4 [1]:
> > - Split from the series [2] as a stand-alone patch, per Michal Hocko
> > - Added Reviewed-by, per Pasha Tatashin
> > - Added Acked-by, per Michal Hocko
> >
> > [1] https://lore.kernel.org/all/20240221194052.927623-7-surenb@xxxxxxxxxx/
> > [2] https://lore.kernel.org/all/20240221194052.927623-1-surenb@xxxxxxxxxx/
> >
> >   include/linux/gfp_types.h | 90 +++++++++++++++++++++++++++------------
> >   1 file changed, 62 insertions(+), 28 deletions(-)
> >
> > diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h
> > index 1b6053da8754..868c8fb1bbc1 100644
> > --- a/include/linux/gfp_types.h
> > +++ b/include/linux/gfp_types.h
> > @@ -21,44 +21,78 @@ typedef unsigned int __bitwise gfp_t;
> >    * include/trace/events/mmflags.h and tools/perf/builtin-kmem.c
> >    */
> >
> > +enum {
> > +     ___GFP_DMA_BIT,
> > +     ___GFP_HIGHMEM_BIT,
> > +     ___GFP_DMA32_BIT,
> > +     ___GFP_MOVABLE_BIT,
> > +     ___GFP_RECLAIMABLE_BIT,
> > +     ___GFP_HIGH_BIT,
> > +     ___GFP_IO_BIT,
> > +     ___GFP_FS_BIT,
> > +     ___GFP_ZERO_BIT,
> > +     ___GFP_UNUSED_BIT,      /* 0x200u unused */
>
> Hi,
>
> what is the need to have this ___GFP_UNUSED_BIT now?

Hi!
We can remove it but then all values will shift. That should be safe
to do now but I prefer one patch to do only one thing. We can add a
separate patch to do further cleanup of unused values.

>
> > +     ___GFP_DIRECT_RECLAIM_BIT,
> > +     ___GFP_KSWAPD_RECLAIM_BIT,
> > +     ___GFP_WRITE_BIT,
> > +     ___GFP_NOWARN_BIT,
> > +     ___GFP_RETRY_MAYFAIL_BIT,
> > +     ___GFP_NOFAIL_BIT,
> > +     ___GFP_NORETRY_BIT,
> > +     ___GFP_MEMALLOC_BIT,
> > +     ___GFP_COMP_BIT,
> > +     ___GFP_NOMEMALLOC_BIT,
> > +     ___GFP_HARDWALL_BIT,
> > +     ___GFP_THISNODE_BIT,
> > +     ___GFP_ACCOUNT_BIT,
> > +     ___GFP_ZEROTAGS_BIT,
> > +#ifdef CONFIG_KASAN_HW_TAGS
> > +     ___GFP_SKIP_ZERO_BIT,
> > +     ___GFP_SKIP_KASAN_BIT,
> > +#endif
> > +#ifdef CONFIG_LOCKDEP
> > +     ___GFP_NOLOCKDEP_BIT,
> > +#endif
> > +     ___GFP_LAST_BIT
> > +};
>
> Does it make sense to have something like:
>    BUILD_BUG_ON(___GFP_LAST_BIT > BITS_PER_LONG, "blah");

I suppose that would not hurt, except gfp_t is unsigned int, not long.
Something like this would work I think:

BUILD_BUG_ON_MSG(___GFP_LAST_BIT > BITS_PER_TYPE(gfp_t), "GFP bit overflow");

except I'm not sure where to put this check. One of the __init
functions in page_alloc.c would probably work but none seem to be
appropriate. mm_core_init() perhaps? Other ideas?

> (should we need to use BIT_ULL() one day)
>
> > +
> >   /* 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_RECLAIMABLE   0x10u
> > -#define ___GFP_HIGH          0x20u
> > -#define ___GFP_IO            0x40u
> > -#define ___GFP_FS            0x80u
> > -#define ___GFP_ZERO          0x100u
> > +#define ___GFP_DMA           BIT(___GFP_DMA_BIT)
> > +#define ___GFP_HIGHMEM               BIT(___GFP_HIGHMEM_BIT)
> > +#define ___GFP_DMA32         BIT(___GFP_DMA32_BIT)
> > +#define ___GFP_MOVABLE               BIT(___GFP_MOVABLE_BIT)
> > +#define ___GFP_RECLAIMABLE   BIT(___GFP_RECLAIMABLE_BIT)
> > +#define ___GFP_HIGH          BIT(___GFP_HIGH_BIT)
> > +#define ___GFP_IO            BIT(___GFP_IO_BIT)
> > +#define ___GFP_FS            BIT(___GFP_FS_BIT)
> > +#define ___GFP_ZERO          BIT(___GFP_ZERO_BIT)
> >   /* 0x200u unused */
>
> Keeping this comment here is now useless, IMHO.

Until the cleanup I would prefer to have it here to denote the gap.
Thanks,
Suren.

>
> CJ
>
> > -#define ___GFP_DIRECT_RECLAIM        0x400u
> > -#define ___GFP_KSWAPD_RECLAIM        0x800u
> > -#define ___GFP_WRITE         0x1000u
> > -#define ___GFP_NOWARN                0x2000u
> > -#define ___GFP_RETRY_MAYFAIL 0x4000u
> > -#define ___GFP_NOFAIL                0x8000u
> > -#define ___GFP_NORETRY               0x10000u
> > -#define ___GFP_MEMALLOC              0x20000u
> > -#define ___GFP_COMP          0x40000u
> > -#define ___GFP_NOMEMALLOC    0x80000u
> > -#define ___GFP_HARDWALL              0x100000u
> > -#define ___GFP_THISNODE              0x200000u
> > -#define ___GFP_ACCOUNT               0x400000u
> > -#define ___GFP_ZEROTAGS              0x800000u
> > +#define ___GFP_DIRECT_RECLAIM        BIT(___GFP_DIRECT_RECLAIM_BIT)
> > +#define ___GFP_KSWAPD_RECLAIM        BIT(___GFP_KSWAPD_RECLAIM_BIT)
> > +#define ___GFP_WRITE         BIT(___GFP_WRITE_BIT)
> > +#define ___GFP_NOWARN                BIT(___GFP_NOWARN_BIT)
> > +#define ___GFP_RETRY_MAYFAIL BIT(___GFP_RETRY_MAYFAIL_BIT)
> > +#define ___GFP_NOFAIL                BIT(___GFP_NOFAIL_BIT)
> > +#define ___GFP_NORETRY               BIT(___GFP_NORETRY_BIT)
> > +#define ___GFP_MEMALLOC              BIT(___GFP_MEMALLOC_BIT)
> > +#define ___GFP_COMP          BIT(___GFP_COMP_BIT)
> > +#define ___GFP_NOMEMALLOC    BIT(___GFP_NOMEMALLOC_BIT)
> > +#define ___GFP_HARDWALL              BIT(___GFP_HARDWALL_BIT)
> > +#define ___GFP_THISNODE              BIT(___GFP_THISNODE_BIT)
> > +#define ___GFP_ACCOUNT               BIT(___GFP_ACCOUNT_BIT)
> > +#define ___GFP_ZEROTAGS              BIT(___GFP_ZEROTAGS_BIT)
> >   #ifdef CONFIG_KASAN_HW_TAGS
> > -#define ___GFP_SKIP_ZERO     0x1000000u
> > -#define ___GFP_SKIP_KASAN    0x2000000u
> > +#define ___GFP_SKIP_ZERO     BIT(___GFP_SKIP_ZERO_BIT)
> > +#define ___GFP_SKIP_KASAN    BIT(___GFP_SKIP_KASAN_BIT)
> >   #else
> >   #define ___GFP_SKIP_ZERO    0
> >   #define ___GFP_SKIP_KASAN   0
> >   #endif
> >   #ifdef CONFIG_LOCKDEP
> > -#define ___GFP_NOLOCKDEP     0x4000000u
> > +#define ___GFP_NOLOCKDEP     BIT(___GFP_NOLOCKDEP_BIT)
> >   #else
> >   #define ___GFP_NOLOCKDEP    0
> >   #endif
> > -/* If the above are modified, __GFP_BITS_SHIFT may need updating */
> >
> >   /*
> >    * Physical address zone modifiers (see linux/mmzone.h - low four bits)
> > @@ -249,7 +283,7 @@ typedef unsigned int __bitwise gfp_t;
> >   #define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP)
> >
> >   /* Room for N __GFP_FOO bits */
> > -#define __GFP_BITS_SHIFT (26 + IS_ENABLED(CONFIG_LOCKDEP))
> > +#define __GFP_BITS_SHIFT ___GFP_LAST_BIT
> >   #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
> >
> >   /**
> >
> > base-commit: 603c04e27c3e9891ce7afa5cd6b496bfacff4206
>