Re: [PATCH v2 06/39] mm: enumerate all gfp flags

From: Suren Baghdasaryan
Date: Wed Oct 25 2023 - 11:30:03 EST

On Tue, Oct 24, 2023 at 10:47 PM Petr Tesařík <petr@xxxxxxxxxxx> wrote:
>
> On Tue, 24 Oct 2023 06:46:03 -0700
> Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:
>
> > 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>
> > ---
> > 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 6583a58670c5..3fbe624763d9 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 */
> > + ___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
> > +};
> > +
> > /* 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 */
>
> This comment can be also removed here, because it is already stated
> above with the definition of ___GFP_UNUSED_BIT.

Ack.

>
> Then again, I think that the GFP bits have never been compacted after
> Neil Brown removed __GFP_ATOMIC with commit 2973d8229b78 simply because
> that would mean changing definitions of all subsequent GFP flags. FWIW
> I am not aware of any code that would depend on the numeric value of
> ___GFP_* macros, so this patch seems like a good opportunity to change
> the numbering and get rid of this unused 0x200u altogether.
>
> @Neil: I have added you to the conversation in case you want to correct
> my understanding of the unused bit.

Hmm. I would prefer to do that in a separate patch even though it
would be a one-line change. Seems safer to me in case something goes
wrong and we have to bisect and revert it. If that sounds ok I'll post
that in the next version.

>
> Other than that LGTM.

Thanks for the review!
Suren.

>
> Petr T
>
> > -#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))
> >
> > /**
>
>