Commit 830f1111 authored by Trond Myklebust's avatar Trond Myklebust
Browse files

NFS: Replace readdir's use of xxhash() with hash_64() 



Both xxhash() and hash_64() appear to give similarly low collision
rates with a standard linearly increasing readdir offset. They both give
similarly higher collision rates when applied to ext4's offsets.

So switch to using the standard hash_64().

Signed-off-by: default avatarTrond Myklebust <trond.myklebust@hammerspace.com>
parent eb07d5a4

fs/nfs/Kconfig

+0 −4
Original line number Diff line number Diff line
@@ -4,10 +4,6 @@ config NFS_FS 
	depends on INET && FILE_LOCKING && MULTIUSER

	select LOCKD

	select SUNRPC

	select CRYPTO

	select CRYPTO_HASH

	select XXHASH

	select CRYPTO_XXHASH

	select NFS_ACL_SUPPORT if NFS_V3_ACL

	help

	  Choose Y here if you want to access files residing on other

fs/nfs/dir.c

+3 −6
Original line number Diff line number Diff line
@@ -39,7 +39,7 @@ 
#include <linux/sched.h>

#include <linux/kmemleak.h>

#include <linux/xattr.h>

#include <linux/xxhash.h>

#include <linux/hash.h>



#include "delegation.h"

#include "iostat.h"
@@ -350,10 +350,7 @@ static int nfs_readdir_page_array_append(struct page *page, 
 * of directory cookies. Content is addressed by the value of the

 * cookie index of the first readdir entry in a page.

 *

 * The xxhash algorithm is chosen because it is fast, and is supposed

 * to result in a decent flat distribution of hashes.

 *

 * We then select only the first 18 bits to avoid issues with excessive

 * We select only the first 18 bits to avoid issues with excessive

 * memory use for the page cache XArray. 18 bits should allow the caching

 * of 262144 pages of sequences of readdir entries. Since each page holds

 * 127 readdir entries for a typical 64-bit system, that works out to a
@@ -363,7 +360,7 @@ static pgoff_t nfs_readdir_page_cookie_hash(u64 cookie) 
{

	if (cookie == 0)

		return 0;

	return xxhash(&cookie, sizeof(cookie), 0) & NFS_READDIR_COOKIE_MASK;

	return hash_64(cookie, 18);

}



static bool nfs_readdir_page_validate(struct page *page, u64 last_cookie,