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ext4: improve smp scalability for inode generation 

->s_next_generation is protected by s_next_gen_lock but its usage
pattern is very primitive.  We don't actually need sequentially
increasing new generation numbers, so let's use prandom_u32() instead.

Reported-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Theodore Ts'o 2017-11-08 22:23:20 -05:00
parent d77147ff44
commit 2325306802
4 changed files with 4 additions and 12 deletions
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2
fs/ext4/ext4.h
View File

@ -1355,8 +1355,6 @@ struct ext4_sb_info {
int s_first_ino;
unsigned int s_inode_readahead_blks;
unsigned int s_inode_goal;
spinlock_t s_next_gen_lock;
u32 s_next_generation;
u32 s_hash_seed[4];
int s_def_hash_version;
int s_hash_unsigned; /* 3 if hash should be signed, 0 if not */

4
fs/ext4/ialloc.c
View File

@ -1138,9 +1138,7 @@ struct inode *__ext4_new_inode(handle_t *handle, struct inode *dir,
inode->i_ino);
goto out;
}
spin_lock(&sbi->s_next_gen_lock);
inode->i_generation = sbi->s_next_generation++;
spin_unlock(&sbi->s_next_gen_lock);
inode->i_generation = prandom_u32();
/* Precompute checksum seed for inode metadata */
if (ext4_has_metadata_csum(sb)) {

8
fs/ext4/ioctl.c
View File

@ -14,6 +14,7 @@
#include <linux/mount.h>
#include <linux/file.h>
#include <linux/quotaops.h>
#include <linux/random.h>
#include <linux/uuid.h>
#include <linux/uaccess.h>
#include <linux/delay.h>
@ -98,7 +99,6 @@ static long swap_inode_boot_loader(struct super_block *sb,
int err;
struct inode *inode_bl;
struct ext4_inode_info *ei_bl;
struct ext4_sb_info *sbi = EXT4_SB(sb);
if (inode->i_nlink != 1 || !S_ISREG(inode->i_mode))
return -EINVAL;
@ -157,10 +157,8 @@ static long swap_inode_boot_loader(struct super_block *sb,
inode->i_ctime = inode_bl->i_ctime = current_time(inode);
spin_lock(&sbi->s_next_gen_lock);
inode->i_generation = sbi->s_next_generation++;
inode_bl->i_generation = sbi->s_next_generation++;
spin_unlock(&sbi->s_next_gen_lock);
inode->i_generation = prandom_u32();
inode_bl->i_generation = prandom_u32();
ext4_discard_preallocations(inode);

2
fs/ext4/super.c
View File

@ -3982,8 +3982,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
}
sbi->s_gdb_count = db_count;
get_random_bytes(&sbi->s_next_generation, sizeof(u32));
spin_lock_init(&sbi->s_next_gen_lock);
timer_setup(&sbi->s_err_report, print_daily_error_info, 0);