[PATCH 1/6] writeback: balance_dirty_pages() shall write more than dirtied pages

Wu Fengguang
2009-09-23T12:43:46Z

[-- Attachment #1: writeback-ratelimit.patch --]
[-- Type: text/plain, Size: 2371 bytes --]

Some filesystem may choose to write much more than ratelimit_pages
before calling balance_dirty_pages_ratelimited_nr(). So it is safer to
determine number to write based on real number of dirtied pages.

The increased write_chunk may make the dirtier more bumpy. This is
filesystem writers' duty not to dirty too much at a time without
checking the ratelimit.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
mm/page-writeback.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

--- linux.orig/mm/page-writeback.c 2009-09-23 16:31:46.000000000 +0800
+++ linux/mm/page-writeback.c 2009-09-23 16:33:19.000000000 +0800
@@ -44,12 +44,12 @@ static long ratelimit_pages = 32;
/*
* When balance_dirty_pages decides that the caller needs to perform some
* non-background writeback, this is how many pages it will attempt to write.
- * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably
+ * It should be somewhat larger than dirtied pages to ensure that reasonably
* large amounts of I/O are submitted.
*/
-static inline long sync_writeback_pages(void)
+static inline long sync_writeback_pages(unsigned long dirtied)
{
- return ratelimit_pages + ratelimit_pages / 2;
+ return dirtied + dirtied / 2;
}

/* The following parameters are exported via /proc/sys/vm */
@@ -476,7 +476,8 @@ get_dirty_limits(unsigned long *pbackgro
* If we're over `background_thresh' then pdflush is woken to perform some
* writeout.
*/
-static void balance_dirty_pages(struct address_space *mapping)
+static void balance_dirty_pages(struct address_space *mapping,
+ unsigned long write_chunk)
{
long nr_reclaimable, bdi_nr_reclaimable;
long nr_writeback, bdi_nr_writeback;
@@ -484,7 +485,6 @@ static void balance_dirty_pages(struct a
unsigned long dirty_thresh;
unsigned long bdi_thresh;
unsigned long pages_written = 0;
- unsigned long write_chunk = sync_writeback_pages();
unsigned long pause = 1;

struct backing_dev_info *bdi = mapping->backing_dev_info;
@@ -640,9 +640,10 @@ void balance_dirty_pages_ratelimited_nr(
p = &__get_cpu_var(bdp_ratelimits);
*p += nr_pages_dirtied;
if (unlikely(*p >= ratelimit)) {
+ ratelimit = sync_writeback_pages(*p);
*p = 0;
preempt_enable();
- balance_dirty_pages(mapping);
+ balance_dirty_pages(mapping, ratelimit);
return;
}
preempt_enable();