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Re: [PATCH v3 06/10] fs/namei.c: Improve dcache hash function

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On Sat, May 28, 2016 at 03:57:19PM -0400, George Spelvin wrote:

> +static inline unsigned int fold_hash(unsigned long x, unsigned long y)
>  {
> +	y ^= x * GOLDEN_RATIO_64;
> +	y *= GOLDEN_RATIO_64;
> +	return y >> 32;
>  }

So does it make sense to use that pattern here too?

This code doesn't much care about performance, but wants a decent hash
from the stack of class keys.

---
 kernel/locking/lockdep.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 81f1a7107c0e..c8498efcd5d9 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -309,10 +309,12 @@ static struct hlist_head chainhash_table[CHAINHASH_SIZE];
  * It's a 64-bit hash, because it's important for the keys to be
  * unique.
  */
-#define iterate_chain_key(key1, key2) \
-	(((key1) << MAX_LOCKDEP_KEYS_BITS) ^ \
-	((key1) >> (64-MAX_LOCKDEP_KEYS_BITS)) ^ \
-	(key2))
+static inline u64 iterate_chain_key(u64 x, u64 y)
+{
+	y ^= x * GOLDEN_RATIO_64;
+	y *= GOLDEN_RATIO_64;
+	return y;
+}
 
 void lockdep_off(void)
 {

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[PATCH 00/10] String hash improvements "George Spelvin" <linux@sciencehorizons.net> - 2016-05-25 09:30 +0200
  Re: [PATCH 00/10] String hash improvements Geert Uytterhoeven <geert@linux-m68k.org> - 2016-05-25 10:10 +0200
    Re: [PATCH 00/10] String hash improvements "George Spelvin" <linux@sciencehorizons.net> - 2016-05-25 10:20 +0200
      Re: [PATCH 00/10] String hash improvements Geert Uytterhoeven <geert@linux-m68k.org> - 2016-05-25 11:00 +0200
        Re: [PATCH 00/10] String hash improvements "George Spelvin" <linux@sciencehorizons.net> - 2016-05-25 11:10 +0200
  Re: [PATCH 00/10] String hash improvements Linus Torvalds <torvalds@linux-foundation.org> - 2016-05-25 18:10 +0200
    [PATCH v3 01/10] Pull out string hash to <linux/stringhash.h> George Spelvin <linux@sciencehorizons.net> - 2016-05-28 22:00 +0200
    [PATCH v3 04/10] Change hash_64() return value to 32 bits George Spelvin <linux@sciencehorizons.net> - 2016-05-28 22:00 +0200
    [PATCH v3 03/10] <linux/sunrpc/svcauth.h>: Define hash_str() in terms of hashlen_string() George Spelvin <linux@sciencehorizons.net> - 2016-05-28 22:00 +0200
    [PATCH v3 10/10] h8300: Add <asm/hash.h> George Spelvin <linux@sciencehorizons.net> - 2016-05-28 22:00 +0200
    [PATCH v3 07/10] <linux/hash.h>: Add support for architecture-specific functions George Spelvin <linux@sciencehorizons.net> - 2016-05-28 22:00 +0200
      Re: [PATCH v3 07/10] <linux/hash.h>: Add support for  architecture-specific functions Geert Uytterhoeven <geert@linux-m68k.org> - 2016-05-29 10:00 +0200
    [PATCH v3 00/10] String hash improvements George Spelvin <linux@sciencehorizons.net> - 2016-05-28 22:00 +0200
      [PATCH v3 05/10] Eliminate bad hash multipliers from hash_32() and  hash_64() George Spelvin <linux@sciencehorizons.net> - 2016-05-28 22:00 +0200
      [PATCH v3 09/10] microblaze: Add <asm/hash.h> George Spelvin <linux@sciencehorizons.net> - 2016-05-28 22:00 +0200
      [PATCH v3 08/10] m68k: Add <asm/hash.h> George Spelvin <linux@sciencehorizons.net> - 2016-05-28 22:00 +0200
      [PATCH v3 06/10] fs/namei.c: Improve dcache hash function George Spelvin <linux@sciencehorizons.net> - 2016-05-28 22:00 +0200
        Re: [PATCH v3 06/10] fs/namei.c: Improve dcache hash function Peter Zijlstra <peterz@infradead.org> - 2016-05-30 17:20 +0200
          Re: [PATCH v3 06/10] fs/namei.c: Improve dcache hash function "George Spelvin" <linux@sciencehorizons.net> - 2016-05-30 18:10 +0200
            Re: [PATCH v3 06/10] fs/namei.c: Improve dcache hash function Peter Zijlstra <peterz@infradead.org> - 2016-05-30 18:30 +0200
              Re: [PATCH v3 06/10] fs/namei.c: Improve dcache hash function "George Spelvin" <linux@sciencehorizons.net> - 2016-05-30 20:20 +0200
      [PATCH v3 02/10] fs/namei.c: Add hashlen_string() function George Spelvin <linux@sciencehorizons.net> - 2016-05-28 22:10 +0200
      Re: [PATCH v3 00/10] String hash improvements Linus Torvalds <torvalds@linux-foundation.org> - 2016-05-28 22:50 +0200
        Re: [PATCH v3 00/10] String hash improvements "George Spelvin" <linux@sciencehorizons.net> - 2016-05-28 23:00 +0200
  [PATCH v2 00/10] String hash improvements "George Spelvin" <linux@horizon.com> - 2016-05-27 17:00 +0200

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