[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>
1 file changed