[PATCH] don't insert pipe dentries into dentry_hashtable.
We currently insert pipe dentries into the global dentry hashtable. This
is suboptimal because there is currently no way these entries can be used
for a lookup(). (/proc/xxx/fd/xxx uses a different mechanism). Inserting
them in dentry hashtable slows dcache lookups.
To let __dpath() still work correctly (ie not adding a " (deleted)") after
dentry name, we do :
- Right after d_alloc(), pretend they are hashed by clearing the
DCACHE_UNHASHED bit.
- Call d_instantiate() instead of d_add() : dentry is not inserted in
hash table.
__dpath() & friends work as intended during dentry lifetime.
- At dismantle time, once dput() must clear the dentry, setting again
DCACHE_UNHASHED bit inside the custom d_delete() function provided by
pipe code, so that dput() can just kill_it.
This patch, combined with (avoid RCU for never hashed dentries) reduced
time of { pipe(p); close(p[0]); close(p[1]);} on my UP machine (1.6GHz
Pentium-M) from 3.23 us to 2.86 us (But this patch does not depend on other
patches, only bench results)
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Acked-by: David Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/fs/pipe.c b/fs/pipe.c
index b1626f2..ae36b89 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -830,7 +830,14 @@
static struct vfsmount *pipe_mnt __read_mostly;
static int pipefs_delete_dentry(struct dentry *dentry)
{
- return 1;
+ /*
+ * At creation time, we pretended this dentry was hashed
+ * (by clearing DCACHE_UNHASHED bit in d_flags)
+ * At delete time, we restore the truth : not hashed.
+ * (so that dput() can proceed correctly)
+ */
+ dentry->d_flags |= DCACHE_UNHASHED;
+ return 0;
}
static struct dentry_operations pipefs_dentry_operations = {
@@ -891,17 +898,22 @@
if (!inode)
goto err_file;
- sprintf(name, "[%lu]", inode->i_ino);
+ this.len = sprintf(name, "[%lu]", inode->i_ino);
this.name = name;
- this.len = strlen(name);
- this.hash = inode->i_ino; /* will go */
+ this.hash = 0;
err = -ENOMEM;
dentry = d_alloc(pipe_mnt->mnt_sb->s_root, &this);
if (!dentry)
goto err_inode;
dentry->d_op = &pipefs_dentry_operations;
- d_add(dentry, inode);
+ /*
+ * We dont want to publish this dentry into global dentry hash table.
+ * We pretend dentry is already hashed, by unsetting DCACHE_UNHASHED
+ * This permits a working /proc/$pid/fd/XXX on pipes
+ */
+ dentry->d_flags &= ~DCACHE_UNHASHED;
+ d_instantiate(dentry, inode);
f->f_vfsmnt = mntget(pipe_mnt);
f->f_dentry = dentry;
f->f_mapping = inode->i_mapping;
