Via https://lkml.org/lkml/2013/4/10/897, we can know that the relative design idea is to keep scan_target[anon] : scan_target[file] == really_scanned_num[anon] : really_scanned_num[file] But we can find the following snippet in shrink_lruvec(): if (nr_file > nr_anon) { ... } else { ... } However, the above code fragment broke the design idea. We can assume: nr[LRU_ACTIVE_FILE] = 30 nr[LRU_INACTIVE_FILE] = 30 nr[LRU_ACTIVE_ANON] = 0 nr[LRU_INACTIVE_ANON] = 40 When the value of (nr_reclaimed < nr_to_reclaim) become false, there are the following results: nr[LRU_ACTIVE_FILE] = 15 nr[LRU_INACTIVE_FILE] = 15 nr[LRU_ACTIVE_ANON] = 0 nr[LRU_INACTIVE_ANON] = 25 nr_file = 30 nr_anon = 25 file_percent = 30 / 60 = 0.5 anon_percent = 25 / 40 = 0.65 According to the above design idea, we should scan some pages from ANON, but in fact we execute the an error code path due to "if (nr_file > nr_anon)". In this way, nr[lru] is likely to be a negative number. Luckily, "nr[lru] -= min(nr[lru], nr_scanned)" can help us to filter this situation, but it has rebelled against our design idea. Signed-off-by: Chen Yucong <slaoub@xxxxxxxxx> --- mm/vmscan.c | 39 ++++++++++++++++++--------------------- 1 file changed, 18 insertions(+), 21 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index a8ffe4e..2c35e34 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2057,8 +2057,7 @@ out: static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) { unsigned long nr[NR_LRU_LISTS]; - unsigned long targets[NR_LRU_LISTS]; - unsigned long nr_to_scan; + unsigned long file_target, anon_target; enum lru_list lru; unsigned long nr_reclaimed = 0; unsigned long nr_to_reclaim = sc->nr_to_reclaim; @@ -2067,8 +2066,8 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) get_scan_count(lruvec, sc, nr); - /* Record the original scan target for proportional adjustments later */ - memcpy(targets, nr, sizeof(nr)); + file_target = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE]; + anon_target = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON]; /* * Global reclaiming within direct reclaim at DEF_PRIORITY is a normal @@ -2087,8 +2086,8 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) blk_start_plug(&plug); while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] || nr[LRU_INACTIVE_FILE]) { - unsigned long nr_anon, nr_file, percentage; - unsigned long nr_scanned; + unsigned long nr_anon, nr_file, file_percent, anon_percent; + unsigned long nr_to_scan, nr_scanned, percentage; for_each_evictable_lru(lru) { if (nr[lru]) { @@ -2122,16 +2121,19 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) if (!nr_file || !nr_anon) break; - if (nr_file > nr_anon) { - unsigned long scan_target = targets[LRU_INACTIVE_ANON] + - targets[LRU_ACTIVE_ANON] + 1; + file_percent = nr_file * 100 / file_target; + anon_percent = nr_anon * 100 / anon_target; + + if (file_percent > anon_percent) { lru = LRU_BASE; - percentage = nr_anon * 100 / scan_target; + nr_scanned = file_target - nr_file; + nr_to_scan = file_target * (100 - anon_percent) / 100; + percentage = nr[LRU_FILE] * 100 / nr_file; } else { - unsigned long scan_target = targets[LRU_INACTIVE_FILE] + - targets[LRU_ACTIVE_FILE] + 1; lru = LRU_FILE; - percentage = nr_file * 100 / scan_target; + nr_scanned = anon_target - nr_anon; + nr_to_scan = anon_target * (100 - file_percent) / 100; + percentage = nr[LRU_BASE] * 100 / nr_anon; } /* Stop scanning the smaller of the LRU */ @@ -2143,14 +2145,9 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) * scan target and the percentage scanning already complete */ lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE; - nr_scanned = targets[lru] - nr[lru]; - nr[lru] = targets[lru] * (100 - percentage) / 100; - nr[lru] -= min(nr[lru], nr_scanned); - - lru += LRU_ACTIVE; - nr_scanned = targets[lru] - nr[lru]; - nr[lru] = targets[lru] * (100 - percentage) / 100; - nr[lru] -= min(nr[lru], nr_scanned); + nr_to_scan -= min(nr_to_scan, nr_scanned); + nr[lru] = nr_to_scan * percentage / 100; + nr[lru + LRU_ACTIVE] = nr_to_scan - nr[lru]; scan_adjusted = true; } -- 1.7.10.4 -- 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>