(resend)
get_page_state() is showing up on profiles on some big machines. It is
a quite expensive function and it is being called too often.
The patch replaces the hardwired RATELIMIT_PAGES with a calculated
amount based on the amount of memory in the machine and the number of
CPUs.
page-writeback.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++---------
1 files changed, 55 insertions(+), 10 deletions(-)
--- 2.5.31/mm/page-writeback.c~ratelimit-scaling Sat Aug 10 23:29:36 2002
+++ 2.5.31-akpm/mm/page-writeback.c Sat Aug 10 23:29:36 2002
@@ -22,6 +22,8 @@
#include <linux/sysrq.h>
#include <linux/backing-dev.h>
#include <linux/mpage.h>
+#include <linux/notifier.h>
+#include <linux/smp.h>
/*
* The maximum number of pages to writeout in a single bdflush/kupdate
@@ -34,10 +36,9 @@
/*
* After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
- * will look to see if it needs to force writeback or throttling. Probably
- * should be scaled by memory size.
+ * will look to see if it needs to force writeback or throttling.
*/
-#define RATELIMIT_PAGES ((512 * 1024) / PAGE_SIZE)
+static int ratelimit_pages = 32;
/*
* When balance_dirty_pages decides that the caller needs to perform some
@@ -45,8 +46,10 @@
* It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably
* large amounts of I/O are submitted.
*/
-#define SYNC_WRITEBACK_PAGES ((RATELIMIT_PAGES * 3) / 2)
-
+static inline int sync_writeback_pages(void)
+{
+ return ratelimit_pages + ratelimit_pages / 2;
+}
/* The following parameters are exported via /proc/sys/vm */
@@ -119,12 +122,12 @@ void balance_dirty_pages(struct address_
bdi = mapping->backing_dev_info;
if (dirty_and_writeback > sync_thresh) {
- int nr_to_write = SYNC_WRITEBACK_PAGES;
+ int nr_to_write = sync_writeback_pages();
writeback_backing_dev(bdi, &nr_to_write, WB_SYNC_LAST, NULL);
get_page_state(&ps);
} else if (dirty_and_writeback > async_thresh) {
- int nr_to_write = SYNC_WRITEBACK_PAGES;
+ int nr_to_write = sync_writeback_pages();
writeback_backing_dev(bdi, &nr_to_write, WB_SYNC_NONE, NULL);
get_page_state(&ps);
@@ -153,7 +156,7 @@ void balance_dirty_pages_ratelimited(str
int cpu;
cpu = get_cpu();
- if (ratelimits[cpu].count++ >= RATELIMIT_PAGES) {
+ if (ratelimits[cpu].count++ >= ratelimit_pages) {
ratelimits[cpu].count = 0;
put_cpu();
balance_dirty_pages(mapping);
@@ -247,16 +250,56 @@ static void wb_timer_fn(unsigned long un
}
-static int __init wb_timer_init(void)
+/*
+ * If ratelimit_pages is too high then we can get into dirty-data overload
+ * if a large number of processes all perform writes at the same time.
+ * If it is too low then SMP machines will call the (expensive) get_page_state
+ * too often.
+ *
+ * Here we set ratelimit_pages to a level which ensures that when all CPUs are
+ * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
+ * thresholds before writeback cuts in.
+ *
+ * But the limit should not be set too high. Because it also controls the
+ * amount of memory which the balance_dirty_pages() caller has to write back.
+ * If this is too large then the caller will block on the IO queue all the
+ * time. So limit it to four megabytes - the balance_dirty_pages() caller
+ * will write six megabyte chunks, max.
+ */
+
+static void set_ratelimit(void)
+{
+ ratelimit_pages = nr_free_pagecache_pages() / (num_online_cpus() * 32);
+ if (ratelimit_pages < 16)
+ ratelimit_pages = 16;
+ if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
+ ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
+}
+
+static int
+ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
+{
+ set_ratelimit();
+ return 0;
+}
+
+static struct notifier_block ratelimit_nb = {
+ .notifier_call = ratelimit_handler,
+ .next = NULL,
+};
+
+static int __init page_writeback_init(void)
{
init_timer(&wb_timer);
wb_timer.expires = jiffies + (dirty_writeback_centisecs * HZ) / 100;
wb_timer.data = 0;
wb_timer.function = wb_timer_fn;
add_timer(&wb_timer);
+ set_ratelimit();
+ register_cpu_notifier(&ratelimit_nb);
return 0;
}
-module_init(wb_timer_init);
+module_init(page_writeback_init);
/*
* A library function, which implements the vm_writeback a_op. It's fairly
@@ -481,3 +524,5 @@ int __set_page_dirty_nobuffers(struct pa
return ret;
}
EXPORT_SYMBOL(__set_page_dirty_nobuffers);
+
+
.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Thu Aug 15 2002 - 22:00:23 EST