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7e0fb73c52
Pull string hash improvements from George Spelvin:
"This series does several related things:
- Makes the dcache hash (fs/namei.c) useful for general kernel use.
(Thanks to Bruce for noticing the zero-length corner case)
- Converts the string hashes in <linux/sunrpc/svcauth.h> to use the
above.
- Avoids 64-bit multiplies in hash_64() on 32-bit platforms. Two
32-bit multiplies will do well enough.
- Rids the world of the bad hash multipliers in hash_32.
This finishes the job started in commit 689de1d6ca ("Minimal
fix-up of bad hashing behavior of hash_64()")
The vast majority of Linux architectures have hardware support for
32x32-bit multiply and so derive no benefit from "simplified"
multipliers.
The few processors that do not (68000, h8/300 and some models of
Microblaze) have arch-specific implementations added. Those
patches are last in the series.
- Overhauls the dcache hash mixing.
The patch in commit 0fed3ac866 ("namei: Improve hash mixing if
CONFIG_DCACHE_WORD_ACCESS") was an off-the-cuff suggestion.
Replaced with a much more careful design that's simultaneously
faster and better. (My own invention, as there was noting suitable
in the literature I could find. Comments welcome!)
- Modify the hash_name() loop to skip the initial HASH_MIX(). This
would let us salt the hash if we ever wanted to.
- Sort out partial_name_hash().
The hash function is declared as using a long state, even though
it's truncated to 32 bits at the end and the extra internal state
contributes nothing to the result. And some callers do odd things:
- fs/hfs/string.c only allocates 32 bits of state
- fs/hfsplus/unicode.c uses it to hash 16-bit unicode symbols not bytes
- Modify bytemask_from_count to handle inputs of 1..sizeof(long)
rather than 0..sizeof(long)-1. This would simplify users other
than full_name_hash"
Special thanks to Bruce Fields for testing and finding bugs in v1. (I
learned some humbling lessons about "obviously correct" code.)
On the arch-specific front, the m68k assembly has been tested in a
standalone test harness, I've been in contact with the Microblaze
maintainers who mostly don't care, as the hardware multiplier is never
omitted in real-world applications, and I haven't heard anything from
the H8/300 world"
* 'hash' of git://ftp.sciencehorizons.net/linux:
h8300: Add <asm/hash.h>
microblaze: Add <asm/hash.h>
m68k: Add <asm/hash.h>
<linux/hash.h>: Add support for architecture-specific functions
fs/namei.c: Improve dcache hash function
Eliminate bad hash multipliers from hash_32() and hash_64()
Change hash_64() return value to 32 bits
<linux/sunrpc/svcauth.h>: Define hash_str() in terms of hashlen_string()
fs/namei.c: Add hashlen_string() function
Pull out string hash to <linux/stringhash.h>
82 lines
1.2 KiB
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82 lines
1.2 KiB
Text
config H8300
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def_bool y
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select GENERIC_ATOMIC64
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select HAVE_UID16
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select VIRT_TO_BUS
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select GENERIC_IRQ_SHOW
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select FRAME_POINTER
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select GENERIC_CPU_DEVICES
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select MODULES_USE_ELF_RELA
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select GENERIC_CLOCKEVENTS
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select CLKDEV_LOOKUP
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select COMMON_CLK
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select ARCH_WANT_FRAME_POINTERS
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select OF
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select OF_IRQ
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select OF_EARLY_FLATTREE
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select HAVE_MEMBLOCK
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select CLKSRC_OF
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select H8300_TMR8
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select HAVE_KERNEL_GZIP
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select HAVE_KERNEL_LZO
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select HAVE_ARCH_KGDB
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select HAVE_ARCH_HASH
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select CPU_NO_EFFICIENT_FFS
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config RWSEM_GENERIC_SPINLOCK
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def_bool y
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config GENERIC_HWEIGHT
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def_bool y
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config NO_IOPORT_MAP
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def_bool y
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config GENERIC_CSUM
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def_bool y
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config HZ
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int
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default 100
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config NR_CPUS
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int
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default 1
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source "init/Kconfig"
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source "kernel/Kconfig.freezer"
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source "arch/h8300/Kconfig.cpu"
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menu "Kernel Features"
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source "kernel/Kconfig.preempt"
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source "mm/Kconfig"
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endmenu
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menu "Executable file formats"
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source "fs/Kconfig.binfmt"
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endmenu
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source "net/Kconfig"
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source "drivers/Kconfig"
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source "fs/Kconfig"
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menu "Kernel hacking"
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source "lib/Kconfig.debug"
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endmenu
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source "security/Kconfig"
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source "crypto/Kconfig"
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source "lib/Kconfig"
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