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Subject[PATCH 10/18] writeback: avoid extra sync work at enqueue time
This removes writeback_control.wb_start and does more straightforward
sync livelock prevention by setting .older_than_this to prevent extra
inodes from being enqueued in the first place.

Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
fs/fs-writeback.c | 16 +++-------------
include/linux/writeback.h | 3 ---
2 files changed, 3 insertions(+), 16 deletions(-)
--- linux-next.orig/fs/fs-writeback.c 2011-05-24 11:17:21.000000000 +0800
+++ linux-next/fs/fs-writeback.c 2011-05-24 11:17:22.000000000 +0800
@@ -544,15 +544,6 @@ static int writeback_sb_inodes(struct su
continue;
}

- /*
- * Was this inode dirtied after sync_sb_inodes was called?
- * This keeps sync from extra jobs and livelock.
- */
- if (inode_dirtied_after(inode, wbc->wb_start)) {
- spin_unlock(&inode->i_lock);
- return 1;
- }
-
__iget(inode);

pages_skipped = wbc->pages_skipped;
@@ -585,9 +576,6 @@ static void __writeback_inodes_wb(struct
{
int ret = 0;

- if (!wbc->wb_start)
- wbc->wb_start = jiffies; /* livelock avoidance */
-
while (!list_empty(&wb->b_io)) {
struct inode *inode = wb_inode(wb->b_io.prev);
struct super_block *sb = inode->i_sb;
@@ -686,7 +674,9 @@ static long wb_writeback(struct bdi_writ
if (wbc.sync_mode == WB_SYNC_ALL || wbc.tagged_writepages)
write_chunk = LONG_MAX;

- wbc.wb_start = jiffies; /* livelock avoidance */
+ oldest_jif = jiffies;
+ wbc.older_than_this = &oldest_jif;
+
spin_lock(&wb->list_lock);
for (;;) {
/*
--- linux-next.orig/include/linux/writeback.h 2011-05-24 11:17:20.000000000 +0800
+++ linux-next/include/linux/writeback.h 2011-05-24 11:17:22.000000000 +0800
@@ -26,9 +26,6 @@ struct writeback_control {
enum writeback_sync_modes sync_mode;
unsigned long *older_than_this; /* If !NULL, only write back inodes
older than this */
- unsigned long wb_start; /* Time writeback_inodes_wb was
- called. This is needed to avoid
- extra jobs and livelock */
long nr_to_write; /* Write this many pages, and decrement
this for each page written */
long pages_skipped; /* Pages which were not written */



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