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Subject[PATCH 01/17] writeback: introduce .tagged_sync for the WB_SYNC_NONE sync stage
sync(2) is performed in two stages: the WB_SYNC_NONE sync and the
WB_SYNC_ALL sync. Tag the first stage with wbc.tagged_sync and do
livelock prevention for it, too.

Note that writeback_inodes_sb() is called by not only sync(), they are
treated the same because the other callers also need livelock prevention.

Impact: It changes the order in which pages/inodes are synced to disk.
Now in the WB_SYNC_NONE stage, it won't proceed to write the next inode
until finished with the current inode.

Acked-by: Jan Kara <jack@suse.cz>
CC: Dave Chinner <david@fromorbit.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
fs/ext4/inode.c | 4 ++--
fs/fs-writeback.c | 9 +++++----
include/linux/writeback.h | 1 +
mm/page-writeback.c | 4 ++--
4 files changed, 10 insertions(+), 8 deletions(-)
--- linux-next.orig/fs/fs-writeback.c 2011-05-05 23:29:51.000000000 +0800
+++ linux-next/fs/fs-writeback.c 2011-05-05 23:30:22.000000000 +0800
@@ -36,6 +36,7 @@ struct wb_writeback_work {
long nr_pages;
struct super_block *sb;
enum writeback_sync_modes sync_mode;
+ unsigned int tagged_sync:1;
unsigned int for_kupdate:1;
unsigned int range_cyclic:1;
unsigned int for_background:1;
@@ -650,6 +651,7 @@ static long wb_writeback(struct bdi_writ
{
struct writeback_control wbc = {
.sync_mode = work->sync_mode,
+ .tagged_sync = work->tagged_sync,
.older_than_this = NULL,
.for_kupdate = work->for_kupdate,
.for_background = work->for_background,
@@ -657,7 +659,7 @@ static long wb_writeback(struct bdi_writ
};
unsigned long oldest_jif;
long wrote = 0;
- long write_chunk;
+ long write_chunk = MAX_WRITEBACK_PAGES;
struct inode *inode;

if (wbc.for_kupdate) {
@@ -683,9 +685,7 @@ static long wb_writeback(struct bdi_writ
* (quickly) tag currently dirty pages
* (maybe slowly) sync all tagged pages
*/
- if (wbc.sync_mode == WB_SYNC_NONE)
- write_chunk = MAX_WRITEBACK_PAGES;
- else
+ if (wbc.sync_mode == WB_SYNC_ALL || wbc.tagged_sync)
write_chunk = LONG_MAX;

wbc.wb_start = jiffies; /* livelock avoidance */
@@ -1193,6 +1193,7 @@ void writeback_inodes_sb_nr(struct super
struct wb_writeback_work work = {
.sb = sb,
.sync_mode = WB_SYNC_NONE,
+ .tagged_sync = 1,
.done = &done,
.nr_pages = nr,
};
--- linux-next.orig/include/linux/writeback.h 2011-05-05 23:29:51.000000000 +0800
+++ linux-next/include/linux/writeback.h 2011-05-05 23:30:22.000000000 +0800
@@ -47,6 +47,7 @@ struct writeback_control {
unsigned encountered_congestion:1; /* An output: a queue is full */
unsigned for_kupdate:1; /* A kupdate writeback */
unsigned for_background:1; /* A background writeback */
+ unsigned tagged_sync:1; /* do livelock prevention for sync */
unsigned for_reclaim:1; /* Invoked from the page allocator */
unsigned range_cyclic:1; /* range_start is cyclic */
unsigned more_io:1; /* more io to be dispatched */
--- linux-next.orig/mm/page-writeback.c 2011-05-05 23:29:51.000000000 +0800
+++ linux-next/mm/page-writeback.c 2011-05-05 23:30:22.000000000 +0800
@@ -892,12 +892,12 @@ int write_cache_pages(struct address_spa
range_whole = 1;
cycled = 1; /* ignore range_cyclic tests */
}
- if (wbc->sync_mode == WB_SYNC_ALL)
+ if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_sync)
tag = PAGECACHE_TAG_TOWRITE;
else
tag = PAGECACHE_TAG_DIRTY;
retry:
- if (wbc->sync_mode == WB_SYNC_ALL)
+ if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_sync)
tag_pages_for_writeback(mapping, index, end);
done_index = index;
while (!done && (index <= end)) {
--- linux-next.orig/fs/ext4/inode.c 2011-05-05 23:29:51.000000000 +0800
+++ linux-next/fs/ext4/inode.c 2011-05-05 23:30:22.000000000 +0800
@@ -2741,7 +2741,7 @@ static int write_cache_pages_da(struct a
index = wbc->range_start >> PAGE_CACHE_SHIFT;
end = wbc->range_end >> PAGE_CACHE_SHIFT;

- if (wbc->sync_mode == WB_SYNC_ALL)
+ if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_sync)
tag = PAGECACHE_TAG_TOWRITE;
else
tag = PAGECACHE_TAG_DIRTY;
@@ -2975,7 +2975,7 @@ static int ext4_da_writepages(struct add
}

retry:
- if (wbc->sync_mode == WB_SYNC_ALL)
+ if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_sync)
tag_pages_for_writeback(mapping, index, end);

while (!ret && wbc->nr_to_write > 0) {



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