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writeback: Refactor writeback_single_inode()

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The code in writeback_single_inode() is relatively complex. The list requeing
logic makes sense only for flusher thread but not really for sync_inode() or
write_inode_now() callers. Also when we want to get rid of inode references
held by flusher thread, we will need a special I_SYNC handling there.

So separate part of writeback_single_inode() which does the real writeback work
into __writeback_single_inode() and make writeback_single_inode() do only stuff
necessary for callers writing only one inode, moving the special list handling
into writeback_sb_inodes(). As a sideeffect this fixes a possible race where we
could skip some inode during sync(2) because other writer refiled it from b_io
to b_dirty list. Also I_SYNC handling is moved into the callers of
__writeback_single_inode() to make locking easier.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
This commit is contained in:
Jan Kara 2012-05-03 14:48:00 +02:00 committed by Fengguang Wu
parent f0d07b7ffd
commit 4f8ad655db
1 changed files with 86 additions and 56 deletions
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142
fs/fs-writeback.c
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@ -364,6 +364,15 @@ static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
(wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
inode->dirtied_when = jiffies;
if (wbc->pages_skipped) {
/*
* writeback is not making progress due to locked
* buffers. Skip this inode for now.
*/
redirty_tail(inode, wb);
return;
}
if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
/*
* We didn't write back all the pages. nfs_writepages()
@ -396,46 +405,20 @@ static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
}
/*
* Write out an inode's dirty pages. Called under wb->list_lock and
* inode->i_lock. Either the caller has an active reference on the inode or
* the inode has I_WILL_FREE set.
*
* If `wait' is set, wait on the writeout.
*
* The whole writeout design is quite complex and fragile. We want to avoid
* starvation of particular inodes when others are being redirtied, prevent
* livelocks, etc.
* Write out an inode and its dirty pages. Do not update the writeback list
* linkage. That is left to the caller. The caller is also responsible for
* setting I_SYNC flag and calling inode_sync_complete() to clear it.
*/
static int
writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
struct writeback_control *wbc)
__writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
struct writeback_control *wbc)
{
struct address_space *mapping = inode->i_mapping;
long nr_to_write = wbc->nr_to_write;
unsigned dirty;
int ret;
assert_spin_locked(&inode->i_lock);
if (!atomic_read(&inode->i_count))
WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
else
WARN_ON(inode->i_state & I_WILL_FREE);
if (inode->i_state & I_SYNC) {
if (wbc->sync_mode != WB_SYNC_ALL)
return 0;
/*
* It's a data-integrity sync. We must wait.
*/
inode_wait_for_writeback(inode);
}
BUG_ON(inode->i_state & I_SYNC);
/* Set I_SYNC, reset I_DIRTY_PAGES */
inode->i_state |= I_SYNC;
spin_unlock(&inode->i_lock);
WARN_ON(!(inode->i_state & I_SYNC));
ret = do_writepages(mapping, wbc);
@ -468,12 +451,65 @@ writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
if (ret == 0)
ret = err;
}
trace_writeback_single_inode(inode, wbc, nr_to_write);
return ret;
}
/*
* Write out an inode's dirty pages. Either the caller has an active reference
* on the inode or the inode has I_WILL_FREE set.
*
* This function is designed to be called for writing back one inode which
* we go e.g. from filesystem. Flusher thread uses __writeback_single_inode()
* and does more profound writeback list handling in writeback_sb_inodes().
*/
static int
writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
struct writeback_control *wbc)
{
int ret = 0;
spin_lock(&inode->i_lock);
if (!atomic_read(&inode->i_count))
WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
else
WARN_ON(inode->i_state & I_WILL_FREE);
if (inode->i_state & I_SYNC) {
if (wbc->sync_mode != WB_SYNC_ALL)
goto out;
/*
* It's a data-integrity sync. We must wait.
*/
inode_wait_for_writeback(inode);
}
WARN_ON(inode->i_state & I_SYNC);
/*
* Skip inode if it is clean. We don't want to mess with writeback
* lists in this function since flusher thread may be doing for example
* sync in parallel and if we move the inode, it could get skipped. So
* here we make sure inode is on some writeback list and leave it there
* unless we have completely cleaned the inode.
*/
if (!(inode->i_state & I_DIRTY))
goto out;
inode->i_state |= I_SYNC;
spin_unlock(&inode->i_lock);
ret = __writeback_single_inode(inode, wb, wbc);
spin_lock(&wb->list_lock);
spin_lock(&inode->i_lock);
requeue_inode(inode, wb, wbc);
/*
* If inode is clean, remove it from writeback lists. Otherwise don't
* touch it. See comment above for explanation.
*/
if (!(inode->i_state & I_DIRTY))
list_del_init(&inode->i_wb_list);
spin_unlock(&wb->list_lock);
inode_sync_complete(inode);
trace_writeback_single_inode(inode, wbc, nr_to_write);
out:
spin_unlock(&inode->i_lock);
return ret;
}
@ -585,23 +621,29 @@ static long writeback_sb_inodes(struct super_block *sb,
spin_unlock(&wb->list_lock);
__iget(inode);
/*
* We already requeued the inode if it had I_SYNC set and we
* are doing WB_SYNC_NONE writeback. So this catches only the
* WB_SYNC_ALL case.
*/
if (inode->i_state & I_SYNC)
inode_wait_for_writeback(inode);
inode->i_state |= I_SYNC;
spin_unlock(&inode->i_lock);
write_chunk = writeback_chunk_size(wb->bdi, work);
wbc.nr_to_write = write_chunk;
wbc.pages_skipped = 0;
writeback_single_inode(inode, wb, &wbc);
__writeback_single_inode(inode, wb, &wbc);
work->nr_pages -= write_chunk - wbc.nr_to_write;
wrote += write_chunk - wbc.nr_to_write;
spin_lock(&wb->list_lock);
spin_lock(&inode->i_lock);
if (!(inode->i_state & I_DIRTY))
wrote++;
if (wbc.pages_skipped) {
/*
* writeback is not making progress due to locked
* buffers. Skip this inode for now.
*/
redirty_tail(inode, wb);
}
requeue_inode(inode, wb, &wbc);
inode_sync_complete(inode);
spin_unlock(&inode->i_lock);
spin_unlock(&wb->list_lock);
iput(inode);
@ -1337,7 +1379,6 @@ EXPORT_SYMBOL(sync_inodes_sb);
int write_inode_now(struct inode *inode, int sync)
{
struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
int ret;
struct writeback_control wbc = {
.nr_to_write = LONG_MAX,
.sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
@ -1349,11 +1390,7 @@ int write_inode_now(struct inode *inode, int sync)
wbc.nr_to_write = 0;
might_sleep();
spin_lock(&inode->i_lock);
ret = writeback_single_inode(inode, wb, &wbc);
spin_unlock(&inode->i_lock);
spin_unlock(&wb->list_lock);
return ret;
return writeback_single_inode(inode, wb, &wbc);
}
EXPORT_SYMBOL(write_inode_now);
@ -1370,14 +1407,7 @@ EXPORT_SYMBOL(write_inode_now);
*/
int sync_inode(struct inode *inode, struct writeback_control *wbc)
{
struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
int ret;
spin_lock(&inode->i_lock);
ret = writeback_single_inode(inode, wb, wbc);
spin_unlock(&inode->i_lock);
spin_unlock(&wb->list_lock);
return ret;
return writeback_single_inode(inode, &inode_to_bdi(inode)->wb, wbc);
}
EXPORT_SYMBOL(sync_inode);