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authorNick Piggin <npiggin@suse.de>2008-12-01 09:33:43 +0100
committerAl Viro <viro@zeniv.linux.org.uk>2008-12-31 18:07:38 -0500
commitc2452f32786159ed85f0e4b21fec09258f822fc8 (patch)
tree50d93df47f4547a5699c87a608e85596e4c6165f
parente2b689d82c0394e5239a3557a217f19e2f47f1be (diff)
shrink struct dentry
struct dentry is one of the most critical structures in the kernel. So it's sad to see it going neglected. With CONFIG_PROFILING turned on (which is probably the common case at least for distros and kernel developers), sizeof(struct dcache) == 208 here (64-bit). This gives 19 objects per slab. I packed d_mounted into a hole, and took another 4 bytes off the inline name length to take the padding out from the end of the structure. This shinks it to 200 bytes. I could have gone the other way and increased the length to 40, but I'm aiming for a magic number, read on... I then got rid of the d_cookie pointer. This shrinks it to 192 bytes. Rant: why was this ever a good idea? The cookie system should increase its hash size or use a tree or something if lookups are a problem. Also the "fast dcookie lookups" in oprofile should be moved into the dcookie code -- how can oprofile possibly care about the dcookie_mutex? It gets dropped after get_dcookie() returns so it can't be providing any sort of protection. At 192 bytes, 21 objects fit into a 4K page, saving about 3MB on my system with ~140 000 entries allocated. 192 is also a multiple of 64, so we get nice cacheline alignment on 64 and 32 byte line systems -- any given dentry will now require 3 cachelines to touch all fields wheras previously it would require 4. I know the inline name size was chosen quite carefully, however with the reduction in cacheline footprint, it should actually be just about as fast to do a name lookup for a 36 character name as it was before the patch (and faster for other sizes). The memory footprint savings for names which are <= 32 or > 36 bytes long should more than make up for the memory cost for 33-36 byte names. Performance is a feature... Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r--arch/powerpc/oprofile/cell/spu_task_sync.c2
-rw-r--r--drivers/oprofile/buffer_sync.c2
-rw-r--r--fs/dcache.c4
-rw-r--r--fs/dcookies.c28
-rw-r--r--include/linux/dcache.h21
5 files changed, 35 insertions, 22 deletions
diff --git a/arch/powerpc/oprofile/cell/spu_task_sync.c b/arch/powerpc/oprofile/cell/spu_task_sync.c
index 2949126d28d1..6b793aeda72e 100644
--- a/arch/powerpc/oprofile/cell/spu_task_sync.c
+++ b/arch/powerpc/oprofile/cell/spu_task_sync.c
@@ -297,7 +297,7 @@ static inline unsigned long fast_get_dcookie(struct path *path)
{
unsigned long cookie;
- if (path->dentry->d_cookie)
+ if (path->dentry->d_flags & DCACHE_COOKIE)
return (unsigned long)path->dentry;
get_dcookie(path, &cookie);
return cookie;
diff --git a/drivers/oprofile/buffer_sync.c b/drivers/oprofile/buffer_sync.c
index 737bd9484822..65e8294a9e29 100644
--- a/drivers/oprofile/buffer_sync.c
+++ b/drivers/oprofile/buffer_sync.c
@@ -200,7 +200,7 @@ static inline unsigned long fast_get_dcookie(struct path *path)
{
unsigned long cookie;
- if (path->dentry->d_cookie)
+ if (path->dentry->d_flags & DCACHE_COOKIE)
return (unsigned long)path->dentry;
get_dcookie(path, &cookie);
return cookie;
diff --git a/fs/dcache.c b/fs/dcache.c
index a1d86c7f3e66..fd244c7a7cc0 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -34,7 +34,6 @@
#include <linux/bootmem.h>
#include "internal.h"
-
int sysctl_vfs_cache_pressure __read_mostly = 100;
EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
@@ -948,9 +947,6 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
dentry->d_op = NULL;
dentry->d_fsdata = NULL;
dentry->d_mounted = 0;
-#ifdef CONFIG_PROFILING
- dentry->d_cookie = NULL;
-#endif
INIT_HLIST_NODE(&dentry->d_hash);
INIT_LIST_HEAD(&dentry->d_lru);
INIT_LIST_HEAD(&dentry->d_subdirs);
diff --git a/fs/dcookies.c b/fs/dcookies.c
index 855d4b1d619a..180e9fec4ad8 100644
--- a/fs/dcookies.c
+++ b/fs/dcookies.c
@@ -93,10 +93,15 @@ static struct dcookie_struct *alloc_dcookie(struct path *path)
{
struct dcookie_struct *dcs = kmem_cache_alloc(dcookie_cache,
GFP_KERNEL);
+ struct dentry *d;
if (!dcs)
return NULL;
- path->dentry->d_cookie = dcs;
+ d = path->dentry;
+ spin_lock(&d->d_lock);
+ d->d_flags |= DCACHE_COOKIE;
+ spin_unlock(&d->d_lock);
+
dcs->path = *path;
path_get(path);
hash_dcookie(dcs);
@@ -119,14 +124,14 @@ int get_dcookie(struct path *path, unsigned long *cookie)
goto out;
}
- dcs = path->dentry->d_cookie;
-
- if (!dcs)
+ if (path->dentry->d_flags & DCACHE_COOKIE) {
+ dcs = find_dcookie((unsigned long)path->dentry);
+ } else {
dcs = alloc_dcookie(path);
-
- if (!dcs) {
- err = -ENOMEM;
- goto out;
+ if (!dcs) {
+ err = -ENOMEM;
+ goto out;
+ }
}
*cookie = dcookie_value(dcs);
@@ -251,7 +256,12 @@ out_kmem:
static void free_dcookie(struct dcookie_struct * dcs)
{
- dcs->path.dentry->d_cookie = NULL;
+ struct dentry *d = dcs->path.dentry;
+
+ spin_lock(&d->d_lock);
+ d->d_flags &= ~DCACHE_COOKIE;
+ spin_unlock(&d->d_lock);
+
path_put(&dcs->path);
kmem_cache_free(dcookie_cache, dcs);
}
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index a37359d0bad1..c66d22487bf8 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -75,14 +75,22 @@ full_name_hash(const unsigned char *name, unsigned int len)
return end_name_hash(hash);
}
-struct dcookie_struct;
-
-#define DNAME_INLINE_LEN_MIN 36
+/*
+ * Try to keep struct dentry aligned on 64 byte cachelines (this will
+ * give reasonable cacheline footprint with larger lines without the
+ * large memory footprint increase).
+ */
+#ifdef CONFIG_64BIT
+#define DNAME_INLINE_LEN_MIN 32 /* 192 bytes */
+#else
+#define DNAME_INLINE_LEN_MIN 40 /* 128 bytes */
+#endif
struct dentry {
atomic_t d_count;
unsigned int d_flags; /* protected by d_lock */
spinlock_t d_lock; /* per dentry lock */
+ int d_mounted;
struct inode *d_inode; /* Where the name belongs to - NULL is
* negative */
/*
@@ -107,10 +115,7 @@ struct dentry {
struct dentry_operations *d_op;
struct super_block *d_sb; /* The root of the dentry tree */
void *d_fsdata; /* fs-specific data */
-#ifdef CONFIG_PROFILING
- struct dcookie_struct *d_cookie; /* cookie, if any */
-#endif
- int d_mounted;
+
unsigned char d_iname[DNAME_INLINE_LEN_MIN]; /* small names */
};
@@ -177,6 +182,8 @@ d_iput: no no no yes
#define DCACHE_INOTIFY_PARENT_WATCHED 0x0020 /* Parent inode is watched */
+#define DCACHE_COOKIE 0x0040 /* For use by dcookie subsystem */
+
extern spinlock_t dcache_lock;
extern seqlock_t rename_lock;