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Subject[PATCH 1/3] writeback: introduce wbc.for_sync to cover the two sync stages
sync(2) is performed in two stages: the WB_SYNC_NONE sync and the
WB_SYNC_ALL sync. Tag both stages with wbc.for_sync for livelock
prevention.

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

Impacts:

- 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.

- this adds a new field to the writeback trace events and may possibly
break some scripts.

CC: 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 | 10 ++++++----
include/linux/writeback.h | 1 +
include/trace/events/writeback.h | 10 ++++++++--
mm/page-writeback.c | 4 ++--
5 files changed, 19 insertions(+), 10 deletions(-)
--- linux-next.orig/fs/fs-writeback.c 2011-05-01 06:35:15.000000000 +0800
+++ linux-next/fs/fs-writeback.c 2011-05-01 06:35:17.000000000 +0800
@@ -36,6 +36,7 @@ struct wb_writeback_work {
long nr_pages;
struct super_block *sb;
enum writeback_sync_modes sync_mode;
+ unsigned int for_sync:1;
unsigned int for_kupdate:1;
unsigned int range_cyclic:1;
unsigned int for_background:1;
@@ -645,13 +646,14 @@ static long wb_writeback(struct bdi_writ
struct writeback_control wbc = {
.sync_mode = work->sync_mode,
.older_than_this = NULL,
+ .for_sync = work->for_sync,
.for_kupdate = work->for_kupdate,
.for_background = work->for_background,
.range_cyclic = work->range_cyclic,
};
unsigned long oldest_jif;
long wrote = 0;
- long write_chunk;
+ long write_chunk = MAX_WRITEBACK_PAGES;
struct inode *inode;

if (!wbc.range_cyclic) {
@@ -672,9 +674,7 @@ 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.for_sync)
write_chunk = LONG_MAX;

wbc.wb_start = jiffies; /* livelock avoidance */
@@ -1209,6 +1209,7 @@ void writeback_inodes_sb_nr(struct super
struct wb_writeback_work work = {
.sb = sb,
.sync_mode = WB_SYNC_NONE,
+ .for_sync = 1,
.done = &done,
.nr_pages = nr,
};
@@ -1286,6 +1287,7 @@ void sync_inodes_sb(struct super_block *
struct wb_writeback_work work = {
.sb = sb,
.sync_mode = WB_SYNC_ALL,
+ .for_sync = 1,
.nr_pages = LONG_MAX,
.range_cyclic = 0,
.done = &done,
--- linux-next.orig/include/linux/writeback.h 2011-05-01 06:35:16.000000000 +0800
+++ linux-next/include/linux/writeback.h 2011-05-01 06:35:17.000000000 +0800
@@ -46,6 +46,7 @@ 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 for_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 2011-05-01 06:35:16.000000000 +0800
+++ linux-next/mm/page-writeback.c 2011-05-01 06:35:17.000000000 +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->for_sync)
tag = PAGECACHE_TAG_TOWRITE;
else
tag = PAGECACHE_TAG_DIRTY;
retry:
- if (wbc->sync_mode == WB_SYNC_ALL)
+ if (wbc->for_sync)
tag_pages_for_writeback(mapping, index, end);
done_index = index;
while (!done && (index <= end)) {
--- linux-next.orig/include/trace/events/writeback.h 2011-05-01 06:35:16.000000000 +0800
+++ linux-next/include/trace/events/writeback.h 2011-05-01 06:35:17.000000000 +0800
@@ -17,6 +17,7 @@ DECLARE_EVENT_CLASS(writeback_work_class
__array(char, name, 32)
__field(long, nr_pages)
__field(dev_t, sb_dev)
+ __field(int, for_sync)
__field(int, sync_mode)
__field(int, for_kupdate)
__field(int, range_cyclic)
@@ -26,16 +27,18 @@ DECLARE_EVENT_CLASS(writeback_work_class
strncpy(__entry->name, dev_name(bdi->dev), 32);
__entry->nr_pages = work->nr_pages;
__entry->sb_dev = work->sb ? work->sb->s_dev : 0;
+ __entry->for_sync = work->for_sync;
__entry->sync_mode = work->sync_mode;
__entry->for_kupdate = work->for_kupdate;
__entry->range_cyclic = work->range_cyclic;
__entry->for_background = work->for_background;
),
- TP_printk("bdi %s: sb_dev %d:%d nr_pages=%ld sync_mode=%d "
+ TP_printk("bdi %s: sb_dev %d:%d nr_pages=%ld sync=%d sync_mode=%d "
"kupdate=%d range_cyclic=%d background=%d",
__entry->name,
MAJOR(__entry->sb_dev), MINOR(__entry->sb_dev),
__entry->nr_pages,
+ __entry->for_sync,
__entry->sync_mode,
__entry->for_kupdate,
__entry->range_cyclic,
@@ -96,6 +99,7 @@ DECLARE_EVENT_CLASS(wbc_class,
__array(char, name, 32)
__field(long, nr_to_write)
__field(long, pages_skipped)
+ __field(int, for_sync)
__field(int, sync_mode)
__field(int, for_kupdate)
__field(int, for_background)
@@ -111,6 +115,7 @@ DECLARE_EVENT_CLASS(wbc_class,
strncpy(__entry->name, dev_name(bdi->dev), 32);
__entry->nr_to_write = wbc->nr_to_write;
__entry->pages_skipped = wbc->pages_skipped;
+ __entry->for_sync = wbc->for_sync;
__entry->sync_mode = wbc->sync_mode;
__entry->for_kupdate = wbc->for_kupdate;
__entry->for_background = wbc->for_background;
@@ -123,12 +128,13 @@ DECLARE_EVENT_CLASS(wbc_class,
__entry->range_end = (long)wbc->range_end;
),

- TP_printk("bdi %s: towrt=%ld skip=%ld mode=%d kupd=%d "
+ TP_printk("bdi %s: towrt=%ld skip=%ld sync=%d mode=%d kupd=%d "
"bgrd=%d reclm=%d cyclic=%d more=%d older=0x%lx "
"start=0x%lx end=0x%lx",
__entry->name,
__entry->nr_to_write,
__entry->pages_skipped,
+ __entry->for_sync,
__entry->sync_mode,
__entry->for_kupdate,
__entry->for_background,
--- linux-next.orig/fs/ext4/inode.c 2011-05-01 06:35:15.000000000 +0800
+++ linux-next/fs/ext4/inode.c 2011-05-01 06:35:17.000000000 +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->for_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->for_sync)
tag_pages_for_writeback(mapping, index, end);

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



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