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authorEric Dumazet <dada1@cosmosbay.com>2006-01-08 04:03:32 -0500
committerLinus Torvalds <torvalds@g5.osdl.org>2006-01-08 23:13:58 -0500
commit5160ee6fc891a9ca114be0e90fa6655647bb64b2 (patch)
tree35d3740a777935582af1b78238f20d2c2971ed55 /fs/coda/cache.c
parent21b6bf143d05d77c350d9c6764ae090a877b66ea (diff)
[PATCH] shrink dentry struct
Some long time ago, dentry struct was carefully tuned so that on 32 bits UP, sizeof(struct dentry) was exactly 128, ie a power of 2, and a multiple of memory cache lines. Then RCU was added and dentry struct enlarged by two pointers, with nice results for SMP, but not so good on UP, because breaking the above tuning (128 + 8 = 136 bytes) This patch reverts this unwanted side effect, by using an union (d_u), where d_rcu and d_child are placed so that these two fields can share their memory needs. At the time d_free() is called (and d_rcu is really used), d_child is known to be empty and not touched by the dentry freeing. Lockless lookups only access d_name, d_parent, d_lock, d_op, d_flags (so the previous content of d_child is not needed if said dentry was unhashed but still accessed by a CPU because of RCU constraints) As dentry cache easily contains millions of entries, a size reduction is worth the extra complexity of the ugly C union. Signed-off-by: Eric Dumazet <dada1@cosmosbay.com> Cc: Dipankar Sarma <dipankar@in.ibm.com> Cc: Maneesh Soni <maneesh@in.ibm.com> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: "Paul E. McKenney" <paulmck@us.ibm.com> Cc: Ian Kent <raven@themaw.net> Cc: Paul Jackson <pj@sgi.com> Cc: Al Viro <viro@ftp.linux.org.uk> Cc: Christoph Hellwig <hch@lst.de> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Cc: Neil Brown <neilb@cse.unsw.edu.au> Cc: James Morris <jmorris@namei.org> Cc: Stephen Smalley <sds@epoch.ncsc.mil> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'fs/coda/cache.c')
-rw-r--r--fs/coda/cache.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/coda/cache.c b/fs/coda/cache.c
index 80072fd9b7fa..c607d923350a 100644
--- a/fs/coda/cache.c
+++ b/fs/coda/cache.c
@@ -93,7 +93,7 @@ static void coda_flag_children(struct dentry *parent, int flag)
93 spin_lock(&dcache_lock); 93 spin_lock(&dcache_lock);
94 list_for_each(child, &parent->d_subdirs) 94 list_for_each(child, &parent->d_subdirs)
95 { 95 {
96 de = list_entry(child, struct dentry, d_child); 96 de = list_entry(child, struct dentry, d_u.d_child);
97 /* don't know what to do with negative dentries */ 97 /* don't know what to do with negative dentries */
98 if ( ! de->d_inode ) 98 if ( ! de->d_inode )
99 continue; 99 continue;