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authorTim Chen <tim.c.chen@linux.intel.com>2010-08-09 17:19:05 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-08-09 20:44:58 -0700
commit7e496299d4d2ad8083effed6c5a18313a919edc6 (patch)
tree8324a3fa378d28f6a63c8b5f5a86311e4eea3562
parent27f5e0f694fd0600274a76854636c0749e3bb1f6 (diff)
downloadlinux-7e496299d4d2ad8083effed6c5a18313a919edc6.tar.bz2
tmpfs: make tmpfs scalable with percpu_counter for used blocks
The current implementation of tmpfs is not scalable. We found that stat_lock is contended by multiple threads when we need to get a new page, leading to useless spinning inside this spin lock. This patch makes use of the percpu_counter library to maintain local count of used blocks to speed up getting and returning of pages. So the acquisition of stat_lock is unnecessary for getting and returning blocks, improving the performance of tmpfs on system with large number of cpus. On a 4 socket 32 core NHM-EX system, we saw improvement of 270%. The implementation below has a slight chance of race between threads causing a slight overshoot of the maximum configured blocks. However, any overshoot is small, and is bounded by the number of cpus. This happens when the number of used blocks is slightly below the maximum configured blocks when a thread checks the used block count, and another thread allocates the last block before the current thread does. This should not be a problem for tmpfs, as the overshoot is most likely to be a few blocks and bounded. If a strict limit is really desired, then configured the max blocks to be the limit less the number of cpus in system. Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com> Cc: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/shmem_fs.h3
-rw-r--r--mm/shmem.c40
2 files changed, 19 insertions, 24 deletions
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index e164291fb3e7..399be5ad2f99 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -3,6 +3,7 @@
#include <linux/swap.h>
#include <linux/mempolicy.h>
+#include <linux/percpu_counter.h>
/* inode in-kernel data */
@@ -23,7 +24,7 @@ struct shmem_inode_info {
struct shmem_sb_info {
unsigned long max_blocks; /* How many blocks are allowed */
- unsigned long free_blocks; /* How many are left for allocation */
+ struct percpu_counter used_blocks; /* How many are allocated */
unsigned long max_inodes; /* How many inodes are allowed */
unsigned long free_inodes; /* How many are left for allocation */
spinlock_t stat_lock; /* Serialize shmem_sb_info changes */
diff --git a/mm/shmem.c b/mm/shmem.c
index f65f84062db5..0618fdad406c 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -28,6 +28,7 @@
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/module.h>
+#include <linux/percpu_counter.h>
#include <linux/swap.h>
static struct vfsmount *shm_mnt;
@@ -233,10 +234,10 @@ static void shmem_free_blocks(struct inode *inode, long pages)
{
struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
if (sbinfo->max_blocks) {
- spin_lock(&sbinfo->stat_lock);
- sbinfo->free_blocks += pages;
+ percpu_counter_add(&sbinfo->used_blocks, -pages);
+ spin_lock(&inode->i_lock);
inode->i_blocks -= pages*BLOCKS_PER_PAGE;
- spin_unlock(&sbinfo->stat_lock);
+ spin_unlock(&inode->i_lock);
}
}
@@ -416,19 +417,17 @@ static swp_entry_t *shmem_swp_alloc(struct shmem_inode_info *info, unsigned long
if (sgp == SGP_READ)
return shmem_swp_map(ZERO_PAGE(0));
/*
- * Test free_blocks against 1 not 0, since we have 1 data
+ * Test used_blocks against 1 less max_blocks, since we have 1 data
* page (and perhaps indirect index pages) yet to allocate:
* a waste to allocate index if we cannot allocate data.
*/
if (sbinfo->max_blocks) {
- spin_lock(&sbinfo->stat_lock);
- if (sbinfo->free_blocks <= 1) {
- spin_unlock(&sbinfo->stat_lock);
+ if (percpu_counter_compare(&sbinfo->used_blocks, (sbinfo->max_blocks - 1)) > 0)
return ERR_PTR(-ENOSPC);
- }
- sbinfo->free_blocks--;
+ percpu_counter_inc(&sbinfo->used_blocks);
+ spin_lock(&inode->i_lock);
inode->i_blocks += BLOCKS_PER_PAGE;
- spin_unlock(&sbinfo->stat_lock);
+ spin_unlock(&inode->i_lock);
}
spin_unlock(&info->lock);
@@ -1387,17 +1386,16 @@ repeat:
shmem_swp_unmap(entry);
sbinfo = SHMEM_SB(inode->i_sb);
if (sbinfo->max_blocks) {
- spin_lock(&sbinfo->stat_lock);
- if (sbinfo->free_blocks == 0 ||
+ if ((percpu_counter_compare(&sbinfo->used_blocks, sbinfo->max_blocks) > 0) ||
shmem_acct_block(info->flags)) {
- spin_unlock(&sbinfo->stat_lock);
spin_unlock(&info->lock);
error = -ENOSPC;
goto failed;
}
- sbinfo->free_blocks--;
+ percpu_counter_inc(&sbinfo->used_blocks);
+ spin_lock(&inode->i_lock);
inode->i_blocks += BLOCKS_PER_PAGE;
- spin_unlock(&sbinfo->stat_lock);
+ spin_unlock(&inode->i_lock);
} else if (shmem_acct_block(info->flags)) {
spin_unlock(&info->lock);
error = -ENOSPC;
@@ -1791,17 +1789,16 @@ static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
buf->f_type = TMPFS_MAGIC;
buf->f_bsize = PAGE_CACHE_SIZE;
buf->f_namelen = NAME_MAX;
- spin_lock(&sbinfo->stat_lock);
if (sbinfo->max_blocks) {
buf->f_blocks = sbinfo->max_blocks;
- buf->f_bavail = buf->f_bfree = sbinfo->free_blocks;
+ buf->f_bavail = buf->f_bfree =
+ sbinfo->max_blocks - percpu_counter_sum(&sbinfo->used_blocks);
}
if (sbinfo->max_inodes) {
buf->f_files = sbinfo->max_inodes;
buf->f_ffree = sbinfo->free_inodes;
}
/* else leave those fields 0 like simple_statfs */
- spin_unlock(&sbinfo->stat_lock);
return 0;
}
@@ -2242,7 +2239,6 @@ static int shmem_remount_fs(struct super_block *sb, int *flags, char *data)
{
struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
struct shmem_sb_info config = *sbinfo;
- unsigned long blocks;
unsigned long inodes;
int error = -EINVAL;
@@ -2250,9 +2246,8 @@ static int shmem_remount_fs(struct super_block *sb, int *flags, char *data)
return error;
spin_lock(&sbinfo->stat_lock);
- blocks = sbinfo->max_blocks - sbinfo->free_blocks;
inodes = sbinfo->max_inodes - sbinfo->free_inodes;
- if (config.max_blocks < blocks)
+ if (percpu_counter_compare(&sbinfo->used_blocks, config.max_blocks) > 0)
goto out;
if (config.max_inodes < inodes)
goto out;
@@ -2269,7 +2264,6 @@ static int shmem_remount_fs(struct super_block *sb, int *flags, char *data)
error = 0;
sbinfo->max_blocks = config.max_blocks;
- sbinfo->free_blocks = config.max_blocks - blocks;
sbinfo->max_inodes = config.max_inodes;
sbinfo->free_inodes = config.max_inodes - inodes;
@@ -2344,7 +2338,7 @@ int shmem_fill_super(struct super_block *sb, void *data, int silent)
#endif
spin_lock_init(&sbinfo->stat_lock);
- sbinfo->free_blocks = sbinfo->max_blocks;
+ percpu_counter_init(&sbinfo->used_blocks, 0);
sbinfo->free_inodes = sbinfo->max_inodes;
sb->s_maxbytes = SHMEM_MAX_BYTES;