This patch aims for clean up, not changing behavior. It records the file_targets and anon_target in advance, removing the need for the targets[] array and adjusts the inactive/active lists by the scanning targets.
This patch also adds some comments, making it more readable and clarify. To be clear: most of those comments stem from https://lkml.org/lkml/2014/6/17/17 and https://lkml.org/lkml/2014/6/19/723. Check the file/anon rate of scanning by invoking trace-vmscan-postprocess.pl during the execution of mmtests(config-global-dhp__pagereclaim-performance). FTrace Reclaim Statistics: vmscan The first round of the test: without-patch with-patch Direct reclaims: 4502 4629 Direct reclaim pages scanned: 584978 586063 Direct reclaim file pages scanned: 556080 565488 Direct reclaim anon pages scanned: 28898 20575 Direct reclaim file/anon ratio: 19.242 27.484 Direct reclaim pages reclaimed: 226069 234171 Direct reclaim write file sync I/O: 0 0 Direct reclaim write anon sync I/O: 0 0 Direct reclaim write file async I/O: 0 0 Direct reclaim write anon async I/O: 12 9 Wake kswapd requests: 17676 18974 Time stalled direct reclaim(seconds): 3.40 3.77 Kswapd wakeups: 3369 3566 Kswapd pages scanned: 21777692 21657203 Kswapd file pages scanned: 21312208 21189120 Kswapd anon pages scanned: 465484 468083 Kswapd file/anon ratio: 45.785 45.267 Kswapd pages reclaimed: 15289358 15239544 Kswapd reclaim write file sync I/O: 0 0 Kswapd reclaim write anon sync I/O: 0 0 Kswapd reclaim write file async I/O: 0 0 Kswapd reclaim write anon async I/O: 1064 1077 Time kswapd awake(seconds): 1410.73 1460.54 The second round of the test: without-patch with-patch Direct reclaims: 5455 4034 Direct reclaim pages scanned: 686646 557039 Direct reclaim file pages scanned: 633144 527209 Direct reclaim anon pages scanned: 53502 29830 Direct reclaim file/anon ratio: 11.834 17.673 Direct reclaim pages reclaimed: 272571 202050 Direct reclaim write file sync I/O: 0 0 Direct reclaim write anon sync I/O: 0 0 Direct reclaim write file async I/O: 0 0 Direct reclaim write anon async I/O: 7 5 Wake kswapd requests: 19404 18786 Time stalled direct reclaim(seconds): 3.89 4.52 Kswapd wakeups: 3109 3583 Kswapd pages scanned: 22006470 21619496 Kswapd file pages scanned: 21568763 21165916 Kswapd anon pages scanned: 437707 453580 Kswapd file/anon ratio: 49.276 46.664 Kswapd pages reclaimed: 15363377 15237407 Kswapd reclaim write file sync I/O: 0 0 Kswapd reclaim write anon sync I/O: 0 0 Kswapd reclaim write file async I/O: 0 0 Kswapd reclaim write anon async I/O: 1104 1101 Time kswapd awake(seconds): 1318.28 1486.85 Signed-off-by: Chen Yucong <sla...@gmail.com> --- mm/vmscan.c | 84 ++++++++++++++++++++++++++++++++++++++++------------------- 1 file changed, 57 insertions(+), 27 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index a8ffe4e..ad46a7b 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 +2066,12 @@ 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)); + /* + * Record the original scan target of file and anon for proportional + * adjustments later + */ + 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 @@ -2084,11 +2087,18 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) scan_adjusted = (global_reclaim(sc) && !current_is_kswapd() && sc->priority == DEF_PRIORITY); + /* + * we scanned the LRUs in batches of SWAP_CLUSTER_MAX until the + * requested number of pages were reclaimed. Assuming the scan + * counts do not reach zero prematurely, the ratio between nr_file + * and nr_anon should remain constant. + */ 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_to_scan, nr_scanned; + unsigned long nr_anon, nr_file; + unsigned percentage; for_each_evictable_lru(lru) { if (nr[lru]) { @@ -2104,11 +2114,14 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) continue; /* - * For kswapd and memcg, reclaim at least the number of pages - * requested. Ensure that the anon and file LRUs are scanned - * proportionally what was requested by get_scan_count(). We - * stop reclaiming one LRU and reduce the amount scanning - * proportional to the original scan target. + * In the normal case, file/anon LRUs are scanned at a rate + * proportional to the value of vm.swappiness. get_scan_count() + * calculates the number of pages to scan from each LRU taking + * into account additional factors such as the availability of + * swap. When the requested number of pages have been reclaimed + * we adjust to scan targets to minimize the number of pages + * scanned while maintaining the ratio of file/anon pages that + * are scanned. */ nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE]; nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON]; @@ -2122,35 +2135,52 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) if (!nr_file || !nr_anon) break; + /* + * Scan the bigger of the LRU more while stop scanning the + * smaller of the LRU to keep aging balance between LRUs + */ if (nr_file > nr_anon) { - unsigned long scan_target = targets[LRU_INACTIVE_ANON] + - targets[LRU_ACTIVE_ANON] + 1; + /* + * In order to maintain the original proportion, we + * need to calculate the percentage of anonymous LRUs + * that has already been scanned. In other words, we + * still need to scan file LRUs until they achieve the + * same *percentage*. + */ + percentage = nr_anon * 100 / anon_target; + nr_scanned = file_target - nr_file; + nr_to_scan = file_target * (100 - percentage) / 100; lru = LRU_BASE; - percentage = nr_anon * 100 / scan_target; + + /* + * Here, Recalculating the percentage is just used to + * divide nr_so_scan pages appropriately between active + * and inactive lists. + */ + percentage = nr[LRU_FILE] * 100 / nr_file; } else { - unsigned long scan_target = targets[LRU_INACTIVE_FILE] + - targets[LRU_ACTIVE_FILE] + 1; + percentage = nr_file * 100 / file_target; + nr_scanned = anon_target - nr_anon; + nr_to_scan = anon_target * (100 - percentage) / 100; lru = LRU_FILE; - percentage = nr_file * 100 / scan_target; + percentage = nr[LRU_BASE] * 100 / nr_anon; } + + if (nr_to_scan <= nr_scanned) + break; + nr_to_scan -= nr_scanned; /* Stop scanning the smaller of the LRU */ nr[lru] = 0; nr[lru + LRU_ACTIVE] = 0; /* - * Recalculate the other LRU scan count based on its original - * scan target and the percentage scanning already complete + * Distribute nr_so_scan pages proportionally between active and + * inactive LRU lists. */ 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[lru] = nr_to_scan * percentage / 100; + nr[lru + LRU_ACTIVE] = nr_to_scan - nr[lru]; scan_adjusted = true; } -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
