From: Eric Dumazet Date: Tue, 6 Sep 2005 22:18:16 +0000 (-0700) Subject: [PATCH] struct dentry: place d_hash close to d_parent and d_name to speedup lookups X-Git-Tag: v2.6.14-rc1~635 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3f4bb1f4199b7dc0c958447b1e4898980013b884;p=linux-2.6 [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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/include/linux/dcache.h b/include/linux/dcache.h index 50be290d24..ab04b4f9b0 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 */ };