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Date:   Wed, 25 Oct 2023 07:46:52 +0200
From:   Petr =?UTF-8?B?VGVzYcWZw61r?= <petr@tesarici.cz>
To:     Suren Baghdasaryan <surenb@google.com>, Neil Brown <neilb@suse.de>
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Subject: Re: [PATCH v2 06/39] mm: enumerate all gfp flags
Message-ID: <20231025074652.44bc0eb4@meshulam.tesarici.cz>
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        <20231024134637.3120277-7-surenb@google.com>
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On Tue, 24 Oct 2023 06:46:03 -0700
Suren Baghdasaryan <surenb@google.com> 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 Tesa=C5=99=C3=ADk <petr@tesarici.cz>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
>  include/linux/gfp_types.h | 90 +++++++++++++++++++++++++++------------
>  1 file changed, 62 insertions(+), 28 deletions(-)
>=20
> 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
>   */
> =20
> +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.

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.

Other than that LGTM.

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 */
> =20
>  /*
>   * 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)
> =20
>  /* 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))
> =20
>  /**