It is preferable that no dirty pages are dispatched for cleaning from
the page reclaim path. At normal priorities, this patch prevents kswapd
writing pages.
However, page reclaim does have a requirement that pages be freed
in a particular zone. If it is failing to make sufficient progress
(reclaiming < SWAP_CLUSTER_MAX at any priority priority), the priority
is raised to scan more pages. A priority of DEF_PRIORITY - 3 is
considered to tbe the point where kswapd is getting into trouble
reclaiming pages. If this priority is reached, kswapd will dispatch
pages for writing.
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
mm/vmscan.c | 13 ++++++++-----
1 files changed, 8 insertions(+), 5 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2d3e5b6..e272951 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -719,7 +719,8 @@ static noinline_for_stack void free_page_list(struct list_head *free_pages)
*/
static unsigned long shrink_page_list(struct list_head *page_list,
struct zone *zone,
- struct scan_control *sc)
+ struct scan_control *sc,
+ int priority)
{
LIST_HEAD(ret_pages);
LIST_HEAD(free_pages);
@@ -827,9 +828,11 @@ static unsigned long shrink_page_list(struct list_head *page_list,
/*
* Only kswapd can writeback filesystem pages to
- * avoid risk of stack overflow
+ * avoid risk of stack overflow but do not writeback
+ * unless under significant pressure.
*/
- if (page_is_file_cache(page) && !current_is_kswapd()) {
+ if (page_is_file_cache(page) &&
+ (!current_is_kswapd() || priority >= DEF_PRIORITY - 2)) {
inc_zone_page_state(page, NR_VMSCAN_WRITE_SKIP);
goto keep_locked;
}
@@ -1465,12 +1468,12 @@ shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
spin_unlock_irq(&zone->lru_lock);
- nr_reclaimed = shrink_page_list(&page_list, zone, sc);
+ nr_reclaimed = shrink_page_list(&page_list, zone, sc, priority);
/* Check if we should syncronously wait for writeback */
if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) {
set_reclaim_mode(priority, sc, true);
- nr_reclaimed += shrink_page_list(&page_list, zone, sc);
+ nr_reclaimed += shrink_page_list(&page_list, zone, sc, priority);
}
local_irq_disable();
--
1.7.3.4
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