On Sun, Mar 17, 2013 at 01:04:12PM +0000, Mel Gorman wrote:
>Currently kswapd queues dirty pages for writeback if scanning at an elevated
>priority but the priority kswapd scans at is not related to the number
>of unqueued dirty encountered. Since commit "mm: vmscan: Flatten kswapd
>priority loop", the priority is related to the size of the LRU and the
>zone watermark which is no indication as to whether kswapd should write
>pages or not.
>
>This patch tracks if an excessive number of unqueued dirty pages are being
>encountered at the end of the LRU. If so, it indicates that dirty pages
>are being recycled before flusher threads can clean them and flags the
>zone so that kswapd will start writing pages until the zone is balanced.
>
>Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
>---
> include/linux/mmzone.h | 8 ++++++++
> mm/vmscan.c | 29 +++++++++++++++++++++++------
> 2 files changed, 31 insertions(+), 6 deletions(-)
>
>diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>index ede2749..edd6b98 100644
>--- a/include/linux/mmzone.h
>+++ b/include/linux/mmzone.h
>@@ -495,6 +495,9 @@ typedef enum {
> ZONE_CONGESTED, /* zone has many dirty pages backed by
> * a congested BDI
> */
>+ ZONE_DIRTY, /* reclaim scanning has recently found
>+ * many dirty file pages
>+ */
> } zone_flags_t;
>
> static inline void zone_set_flag(struct zone *zone, zone_flags_t flag)
>@@ -517,6 +520,11 @@ static inline int zone_is_reclaim_congested(const struct zone *zone)
> return test_bit(ZONE_CONGESTED, &zone->flags);
> }
>
>+static inline int zone_is_reclaim_dirty(const struct zone *zone)
>+{
>+ return test_bit(ZONE_DIRTY, &zone->flags);
>+}
>+
> static inline int zone_is_reclaim_locked(const struct zone *zone)
> {
> return test_bit(ZONE_RECLAIM_LOCKED, &zone->flags);
>diff --git a/mm/vmscan.c b/mm/vmscan.c
>index af3bb6f..493728b 100644
>--- a/mm/vmscan.c
>+++ b/mm/vmscan.c
>@@ -675,13 +675,14 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> struct zone *zone,
> struct scan_control *sc,
> enum ttu_flags ttu_flags,
>- unsigned long *ret_nr_dirty,
>+ unsigned long *ret_nr_unqueued_dirty,
> unsigned long *ret_nr_writeback,
> bool force_reclaim)
> {
> LIST_HEAD(ret_pages);
> LIST_HEAD(free_pages);
> int pgactivate = 0;
>+ unsigned long nr_unqueued_dirty = 0;
> unsigned long nr_dirty = 0;
> unsigned long nr_congested = 0;
> unsigned long nr_reclaimed = 0;
>@@ -807,14 +808,17 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> if (PageDirty(page)) {
> nr_dirty++;
>
>+ if (!PageWriteback(page))
>+ nr_unqueued_dirty++;
>+
> /*
> * Only kswapd can writeback filesystem pages to
>- * avoid risk of stack overflow but do not writeback
>- * unless under significant pressure.
>+ * avoid risk of stack overflow but only writeback
>+ * if many dirty pages have been encountered.
> */
> if (page_is_file_cache(page) &&
> (!current_is_kswapd() ||
>- sc->priority >= DEF_PRIORITY - 2)) {
>+ !zone_is_reclaim_dirty(zone))) {
> /*
> * Immediately reclaim when written back.
> * Similar in principal to deactivate_page()
>@@ -959,7 +963,7 @@ keep:
> list_splice(&ret_pages, page_list);
> count_vm_events(PGACTIVATE, pgactivate);
> mem_cgroup_uncharge_end();
>- *ret_nr_dirty += nr_dirty;
>+ *ret_nr_unqueued_dirty += nr_unqueued_dirty;
> *ret_nr_writeback += nr_writeback;
> return nr_reclaimed;
> }
>@@ -1372,6 +1376,15 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
> (nr_taken >> (DEF_PRIORITY - sc->priority)))
> wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
>
>+ /*
>+ * Similarly, if many dirty pages are encountered that are not
>+ * currently being written then flag that kswapd should start
>+ * writing back pages.
>+ */
>+ if (global_reclaim(sc) && nr_dirty &&
>+ nr_dirty >= (nr_taken >> (DEF_PRIORITY - sc->priority)))
>+ zone_set_flag(zone, ZONE_DIRTY);
>+
> trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
> zone_idx(zone),
> nr_scanned, nr_reclaimed,
>@@ -2735,8 +2748,12 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
> end_zone = i;
> break;
> } else {
>- /* If balanced, clear the congested flag */
>+ /*
>+ * If balanced, clear the dirty and congested
>+ * flags
>+ */
> zone_clear_flag(zone, ZONE_CONGESTED);
>+ zone_clear_flag(zone, ZONE_DIRTY);
Hi Mel,
There are two places in balance_pgdat clear ZONE_CONGESTED flag, one
is during scan zone which have free_pages <= high_wmark_pages(zone), the
other one is zone get balanced after reclaim, it seems that you miss the
later one.
Regards,
Wanpeng Li
> }
> }
>
>--
>1.8.1.4
>
>--
>To unsubscribe, send a message with 'unsubscribe linux-mm' in
>the body to majordomo@xxxxxxxxx. For more info on Linux MM,
>see: http://www.linux-mm.org/ .
>Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>