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[PATCH] O(1) sb list traversing on syncs
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This patch removes O(n^2) super block loops in sync_inodes(),
sync_filesystems() etc.  in favour of using __put_super_and_need_restart()
which I introduced earlier.  We faced a noticably long freezes on sb
syncing when there are thousands of super blocks in the system.

Signed-Off-By: Kirill Korotaev <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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Kirill Korotaev authored and Linus Torvalds committed Jun 23, 2005
1 parent 4fea283 commit 618f063
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Showing 3 changed files with 96 additions and 111 deletions.
64 changes: 27 additions & 37 deletions fs/fs-writeback.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -485,32 +485,6 @@ static void set_sb_syncing(int val)
spin_unlock(&sb_lock);
}

/*
* Find a superblock with inodes that need to be synced
*/
static struct super_block *get_super_to_sync(void)
{
struct super_block *sb;
restart:
spin_lock(&sb_lock);
sb = sb_entry(super_blocks.prev);
for (; sb != sb_entry(&super_blocks); sb = sb_entry(sb->s_list.prev)) {
if (sb->s_syncing)
continue;
sb->s_syncing = 1;
sb->s_count++;
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
if (!sb->s_root) {
drop_super(sb);
goto restart;
}
return sb;
}
spin_unlock(&sb_lock);
return NULL;
}

/**
* sync_inodes - writes all inodes to disk
* @wait: wait for completion
Expand All @@ -530,23 +504,39 @@ static struct super_block *get_super_to_sync(void)
* outstanding dirty inodes, the writeback goes block-at-a-time within the
* filesystem's write_inode(). This is extremely slow.
*/
void sync_inodes(int wait)
static void __sync_inodes(int wait)
{
struct super_block *sb;

set_sb_syncing(0);
while ((sb = get_super_to_sync()) != NULL) {
sync_inodes_sb(sb, 0);
sync_blockdev(sb->s_bdev);
drop_super(sb);
spin_lock(&sb_lock);
restart:
list_for_each_entry(sb, &super_blocks, s_list) {
if (sb->s_syncing)
continue;
sb->s_syncing = 1;
sb->s_count++;
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
if (sb->s_root) {
sync_inodes_sb(sb, wait);
sync_blockdev(sb->s_bdev);
}
up_read(&sb->s_umount);
spin_lock(&sb_lock);
if (__put_super_and_need_restart(sb))
goto restart;
}
spin_unlock(&sb_lock);
}

void sync_inodes(int wait)
{
set_sb_syncing(0);
__sync_inodes(0);

if (wait) {
set_sb_syncing(0);
while ((sb = get_super_to_sync()) != NULL) {
sync_inodes_sb(sb, 1);
sync_blockdev(sb->s_bdev);
drop_super(sb);
}
__sync_inodes(1);
}
}

Expand Down
60 changes: 24 additions & 36 deletions fs/quota.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -149,36 +149,6 @@ static int check_quotactl_valid(struct super_block *sb, int type, int cmd, qid_t
return error;
}

static struct super_block *get_super_to_sync(int type)
{
struct list_head *head;
int cnt, dirty;

restart:
spin_lock(&sb_lock);
list_for_each(head, &super_blocks) {
struct super_block *sb = list_entry(head, struct super_block, s_list);

/* This test just improves performance so it needn't be reliable... */
for (cnt = 0, dirty = 0; cnt < MAXQUOTAS; cnt++)
if ((type == cnt || type == -1) && sb_has_quota_enabled(sb, cnt)
&& info_any_dirty(&sb_dqopt(sb)->info[cnt]))
dirty = 1;
if (!dirty)
continue;
sb->s_count++;
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
if (!sb->s_root) {
drop_super(sb);
goto restart;
}
return sb;
}
spin_unlock(&sb_lock);
return NULL;
}

static void quota_sync_sb(struct super_block *sb, int type)
{
int cnt;
Expand Down Expand Up @@ -219,17 +189,35 @@ static void quota_sync_sb(struct super_block *sb, int type)

void sync_dquots(struct super_block *sb, int type)
{
int cnt, dirty;

if (sb) {
if (sb->s_qcop->quota_sync)
quota_sync_sb(sb, type);
return;
}
else {
while ((sb = get_super_to_sync(type)) != NULL) {
if (sb->s_qcop->quota_sync)
quota_sync_sb(sb, type);
drop_super(sb);
}

spin_lock(&sb_lock);
restart:
list_for_each_entry(sb, &super_blocks, s_list) {
/* This test just improves performance so it needn't be reliable... */
for (cnt = 0, dirty = 0; cnt < MAXQUOTAS; cnt++)
if ((type == cnt || type == -1) && sb_has_quota_enabled(sb, cnt)
&& info_any_dirty(&sb_dqopt(sb)->info[cnt]))
dirty = 1;
if (!dirty)
continue;
sb->s_count++;
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
if (sb->s_root && sb->s_qcop->quota_sync)
quota_sync_sb(sb, type);
up_read(&sb->s_umount);
spin_lock(&sb_lock);
if (__put_super_and_need_restart(sb))
goto restart;
}
spin_unlock(&sb_lock);
}

/* Copy parameters and call proper function */
Expand Down
83 changes: 45 additions & 38 deletions fs/super.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -341,20 +341,22 @@ static inline void write_super(struct super_block *sb)
*/
void sync_supers(void)
{
struct super_block * sb;
restart:
struct super_block *sb;

spin_lock(&sb_lock);
sb = sb_entry(super_blocks.next);
while (sb != sb_entry(&super_blocks))
restart:
list_for_each_entry(sb, &super_blocks, s_list) {
if (sb->s_dirt) {
sb->s_count++;
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
write_super(sb);
drop_super(sb);
goto restart;
} else
sb = sb_entry(sb->s_list.next);
up_read(&sb->s_umount);
spin_lock(&sb_lock);
if (__put_super_and_need_restart(sb))
goto restart;
}
}
spin_unlock(&sb_lock);
}

Expand All @@ -381,20 +383,16 @@ void sync_filesystems(int wait)

down(&mutex); /* Could be down_interruptible */
spin_lock(&sb_lock);
for (sb = sb_entry(super_blocks.next); sb != sb_entry(&super_blocks);
sb = sb_entry(sb->s_list.next)) {
list_for_each_entry(sb, &super_blocks, s_list) {
if (!sb->s_op->sync_fs)
continue;
if (sb->s_flags & MS_RDONLY)
continue;
sb->s_need_sync_fs = 1;
}
spin_unlock(&sb_lock);

restart:
spin_lock(&sb_lock);
for (sb = sb_entry(super_blocks.next); sb != sb_entry(&super_blocks);
sb = sb_entry(sb->s_list.next)) {
list_for_each_entry(sb, &super_blocks, s_list) {
if (!sb->s_need_sync_fs)
continue;
sb->s_need_sync_fs = 0;
Expand All @@ -405,8 +403,11 @@ void sync_filesystems(int wait)
down_read(&sb->s_umount);
if (sb->s_root && (wait || sb->s_dirt))
sb->s_op->sync_fs(sb, wait);
drop_super(sb);
goto restart;
up_read(&sb->s_umount);
/* restart only when sb is no longer on the list */
spin_lock(&sb_lock);
if (__put_super_and_need_restart(sb))
goto restart;
}
spin_unlock(&sb_lock);
up(&mutex);
Expand All @@ -422,21 +423,25 @@ void sync_filesystems(int wait)

struct super_block * get_super(struct block_device *bdev)
{
struct list_head *p;
struct super_block *sb;

if (!bdev)
return NULL;
rescan:

spin_lock(&sb_lock);
list_for_each(p, &super_blocks) {
struct super_block *s = sb_entry(p);
if (s->s_bdev == bdev) {
s->s_count++;
rescan:
list_for_each_entry(sb, &super_blocks, s_list) {
if (sb->s_bdev == bdev) {
sb->s_count++;
spin_unlock(&sb_lock);
down_read(&s->s_umount);
if (s->s_root)
return s;
drop_super(s);
goto rescan;
down_read(&sb->s_umount);
if (sb->s_root)
return sb;
up_read(&sb->s_umount);
/* restart only when sb is no longer on the list */
spin_lock(&sb_lock);
if (__put_super_and_need_restart(sb))
goto rescan;
}
}
spin_unlock(&sb_lock);
Expand All @@ -447,20 +452,22 @@ EXPORT_SYMBOL(get_super);

struct super_block * user_get_super(dev_t dev)
{
struct list_head *p;
struct super_block *sb;

rescan:
spin_lock(&sb_lock);
list_for_each(p, &super_blocks) {
struct super_block *s = sb_entry(p);
if (s->s_dev == dev) {
s->s_count++;
rescan:
list_for_each_entry(sb, &super_blocks, s_list) {
if (sb->s_dev == dev) {
sb->s_count++;
spin_unlock(&sb_lock);
down_read(&s->s_umount);
if (s->s_root)
return s;
drop_super(s);
goto rescan;
down_read(&sb->s_umount);
if (sb->s_root)
return sb;
up_read(&sb->s_umount);
/* restart only when sb is no longer on the list */
spin_lock(&sb_lock);
if (__put_super_and_need_restart(sb))
goto rescan;
}
}
spin_unlock(&sb_lock);
Expand Down

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