From c2452f32786159ed85f0e4b21fec09258f822fc8 Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Mon, 1 Dec 2008 09:33:43 +0100 Subject: [PATCH] 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 --- arch/powerpc/oprofile/cell/spu_task_sync.c | 2 +- drivers/oprofile/buffer_sync.c | 2 +- fs/dcache.c | 4 ---- fs/dcookies.c | 28 +++++++++++++++------- include/linux/dcache.h | 21 ++++++++++------ 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 2949126d28d..6b793aeda72 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 737bd948482..65e8294a9e2 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 a1d86c7f3e6..fd244c7a7cc 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -34,7 +34,6 @@ #include #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 855d4b1d619..180e9fec4ad 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 a37359d0bad..c66d22487bf 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; -- 2.41.1