lkml.org 
[lkml]   [2006]   [Nov]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] dont insert pipe dentries into dentry_hashtable.
Date
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 slow 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 the next one (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>
--- linux-2.6.19-rc6/fs/pipe.c 2006-11-22 17:33:52.000000000 +0100
+++ linux-2.6.19-rc6-ed/fs/pipe.c 2006-11-22 17:53:02.000000000 +0100
@@ -830,7 +830,14 @@ void free_pipe_info(struct inode *inode)
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 @@ struct file *create_write_pipe(void)
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;
\
 
 \ /
  Last update: 2006-11-22 18:51    [W:0.131 / U:1.716 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site