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authorEric Dumazet <dada1@cosmosbay.com>2005-09-06 15:18:16 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2005-09-07 16:57:41 -0700
commit3f4bb1f4199b7dc0c958447b1e4898980013b884 (patch)
tree3d8aacfc6b7bbf7b2d224ae10ca693c55c64739e /include/linux
parent0811bab24ff1eecab38110eda7ea7847db95c64e (diff)
downloadblackbird-op-linux-3f4bb1f4199b7dc0c958447b1e4898980013b884.tar.gz
blackbird-op-linux-3f4bb1f4199b7dc0c958447b1e4898980013b884.zip
[PATCH] struct dentry: place d_hash close to d_parent and d_name to speedup lookups
dentry cache uses sophisticated RCU technology (and prefetching if available) but touches 2 cache lines per dentry during hlist lookup. This patch moves d_hash in the same cache line than d_parent and d_name fields so that : 1) One cache line is needed instead of two. 2) the hlist_for_each_rcu() prefetching has a chance to bring all the needed data in advance, not only the part that includes d_hash.next. I also changed one old comment that was wrong for 64bits. A further optimisation would be to separate dentry in two parts, one that is mostly read, and one writen (d_count/d_lock) to avoid false sharing on SMP/NUMA but this would need different field placement depending on 32bits or 64bits platform. Signed-off-by: Eric Dumazet <dada1@cosmosbay.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/dcache.h4
1 files changed, 2 insertions, 2 deletions
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 50be290d24d2..ab04b4f9b0db 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -88,8 +88,9 @@ struct dentry {
* negative */
/*
* The next three fields are touched by __d_lookup. Place them here
- * so they all fit in a 16-byte range, with 16-byte alignment.
+ * so they all fit in a cache line.
*/
+ struct hlist_node d_hash; /* lookup hash list */
struct dentry *d_parent; /* parent directory */
struct qstr d_name;
@@ -103,7 +104,6 @@ struct dentry {
void *d_fsdata; /* fs-specific data */
struct rcu_head d_rcu;
struct dcookie_struct *d_cookie; /* cookie, if any */
- struct hlist_node d_hash; /* lookup hash list */
int d_mounted;
unsigned char d_iname[DNAME_INLINE_LEN_MIN]; /* small names */
};
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