Re: PATCH: Improvements in shrink_mmap and kswapd
From: Roger Larsson <hidden>
Date: 2000-06-18 00:51:31
Hi, Comments below, "Juan J. Quintela" wrote:
Hi
this patch makes kswapd use less resources. It should solve
the kswapd eats xx% of my CPU problems. It appears that it improves
IO a bit here. Could people having problems with IO told me if this
patch improves things, I am interested in knowing that it don't makes
things worst never. This patch is stable here. I am finishing the
deferred mmaped pages form file writing patch, that should solve
several other problems.
Reports of success/failure are welcome. Comments are also welcome.
Later, Juan.+/**
+ * shrink_mmap - Tries to free memory
+ * @priority: how hard we will try to free pages (0 hardest)
+ * @gfp_mask: Restrictions to free pages
+ *
+ * This function walks the lru list searching for free pages. It
+ * returns 1 to indicate success and 0 in the opposite case. It gets a
+ * lock in the pagemap_lru_lock and the pagecache_lock.
*/
+/* nr_to_examinate counts the number of pages that we will read as
+ * maximum as each call. This means that we don't loop.
+ */
+/* nr_writes counts the number of writes that we have started to the
+ * moment. We limitate the number of writes in each round to
+ * max_page_launder. ToDo: Make that variable tunable through sysctl.
+ */
+const int max_page_launder = 100;
+
int shrink_mmap(int priority, int gfp_mask)
{
- int ret = 0, count, nr_dirty;
struct list_head * page_lru;
struct page * page = NULL;
-
- count = nr_lru_pages / (priority + 1);
- nr_dirty = priority;
+ int ret;
+ int nr_to_examinate = nr_lru_pages;Is this really enough? PG_AGE_MAX * nr_lru_pages / (priority + 1) is required to ensure that all pages have been scanned at an age of 0. But that is probably an overkill... there is a sum involved here... PG_AGE_START * ... Could be nice to get rid of streaming pages before other attempts are done.
quoted hunk ↗ jump to hunk
diff -urN --exclude-from=/home/lfcia/quintela/work/kernel/exclude base/mm/vmscan.c working/mm/vmscan.c--- base/mm/vmscan.c Sat Jun 17 23:51:24 2000 +++ working/mm/vmscan.c Sun Jun 18 00:28:12 2000[removed stuff]@@ -427,6 +425,32 @@ return __ret; } +/** + * memory_pressure - Is the system under memory pressure + * + * Returns 1 if the system is low on memory in any of its zones, + * otherwise returns 0. + */ +int memory_pressure(void) +{ + pg_data_t *pgdat = pgdat_list; + + do { + int i; + for(i = 0; i < MAX_NR_ZONES; i++) { + zone_t *zone = pgdat->node_zones + i; + if (!zone->size || !zone->zone_wake_kswapd) + continue; + if (zone->free_pages < zone->pages_low) + return 1; + } + pgdat = pgdat->node_next; + + } while (pgdat); + + return 0; +} +
This function effectively ignore 'zone_wake_kswapd' since it should always be set when free < low - if correct behaviour remove the test.
priority = 64;
do {
while (shrink_mmap(priority, gfp_mask)) {
- ret = 1;
if (!--count)
goto done;
}
+ if(!memory_pressure())
+ return 1;
Needs lower than pages_low after shrink_mmap to pass this test and enter swapping... might be correct behaviour! /RogerL -- Home page: http://www.norran.net/nra02596/ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux.eu.org/Linux-MM/