From: Eric Dumazet Date: Thu, 7 Dec 2006 04:38:45 +0000 (-0800) Subject: [PATCH] don't insert pipe dentries into dentry_hashtable. X-Git-Tag: v2.6.20-rc1~145^2^2~112 X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=d18de5a2721f84ffd6a5d637915746ed47becc1c;p=linux-2.6-omap-h63xx.git [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 Acked-by: David Miller Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/fs/pipe.c b/fs/pipe.c index b1626f269a3..ae36b89b1a3 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -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;