From: Johannes Weiner <hannes@xxxxxxxxxxx> Subject: mm: vmscan: determine anon/file pressure balance at the reclaim root We split the LRU lists into anon and file, and we rebalance the scan pressure between them when one of them begins thrashing: if the file cache experiences workingset refaults, we increase the pressure on anonymous pages; if the workload is stalled on swapins, we increase the pressure on the file cache instead. With cgroups and their nested LRU lists, we currently don't do this correctly. While recursive cgroup reclaim establishes a relative LRU order among the pages of all involved cgroups, LRU pressure balancing is done on an individual cgroup LRU level. As a result, when one cgroup is thrashing on the filesystem cache while a sibling may have cold anonymous pages, pressure doesn't get equalized between them. This patch moves LRU balancing decision to the root of reclaim - the same level where the LRU order is established. It does this by tracking LRU cost recursively, so that every level of the cgroup tree knows the aggregate LRU cost of all memory within its domain. When the page scanner calculates the scan balance for any given individual cgroup's LRU list, it uses the values from the ancestor cgroup that initiated the reclaim cycle. If one sibling is then thrashing on the cache, it will tip the pressure balance inside its ancestors, and the next hierarchical reclaim iteration will go more after the anon pages in the tree. Link: http://lkml.kernel.org/r/20200520232525.798933-13-hannes@xxxxxxxxxxx Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/memcontrol.h | 13 +++++++++++ mm/swap.c | 32 +++++++++++++++++++++++---- mm/vmscan.c | 41 ++++++++++++++--------------------- 3 files changed, 57 insertions(+), 29 deletions(-) --- a/include/linux/memcontrol.h~mm-vmscan-determine-anon-file-pressure-balance-at-the-reclaim-root +++ a/include/linux/memcontrol.h @@ -1242,6 +1242,19 @@ static inline void dec_lruvec_page_state mod_lruvec_page_state(page, idx, -1); } +static inline struct lruvec *parent_lruvec(struct lruvec *lruvec) +{ + struct mem_cgroup *memcg; + + memcg = lruvec_memcg(lruvec); + if (!memcg) + return NULL; + memcg = parent_mem_cgroup(memcg); + if (!memcg) + return NULL; + return mem_cgroup_lruvec(memcg, lruvec_pgdat(lruvec)); +} + #ifdef CONFIG_CGROUP_WRITEBACK struct wb_domain *mem_cgroup_wb_domain(struct bdi_writeback *wb); --- a/mm/swap.c~mm-vmscan-determine-anon-file-pressure-balance-at-the-reclaim-root +++ a/mm/swap.c @@ -282,11 +282,33 @@ void lru_note_cost(struct page *page) { struct lruvec *lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page)); - /* Record new data point */ - if (page_is_file_lru(page)) - lruvec->file_cost++; - else - lruvec->anon_cost++; + do { + unsigned long lrusize; + + /* Record cost event */ + if (page_is_file_lru(page)) + lruvec->file_cost++; + else + lruvec->anon_cost++; + + /* + * Decay previous events + * + * Because workloads change over time (and to avoid + * overflow) we keep these statistics as a floating + * average, which ends up weighing recent refaults + * more than old ones. + */ + lrusize = lruvec_page_state(lruvec, NR_INACTIVE_ANON) + + lruvec_page_state(lruvec, NR_ACTIVE_ANON) + + lruvec_page_state(lruvec, NR_INACTIVE_FILE) + + lruvec_page_state(lruvec, NR_ACTIVE_FILE); + + if (lruvec->file_cost + lruvec->anon_cost > lrusize / 4) { + lruvec->file_cost /= 2; + lruvec->anon_cost /= 2; + } + } while ((lruvec = parent_lruvec(lruvec))); } static void __activate_page(struct page *page, struct lruvec *lruvec, --- a/mm/vmscan.c~mm-vmscan-determine-anon-file-pressure-balance-at-the-reclaim-root +++ a/mm/vmscan.c @@ -79,6 +79,12 @@ struct scan_control { */ struct mem_cgroup *target_mem_cgroup; + /* + * Scan pressure balancing between anon and file LRUs + */ + unsigned long anon_cost; + unsigned long file_cost; + /* Can active pages be deactivated as part of reclaim? */ #define DEACTIVATE_ANON 1 #define DEACTIVATE_FILE 2 @@ -2231,10 +2237,8 @@ static void get_scan_count(struct lruvec int swappiness = mem_cgroup_swappiness(memcg); u64 fraction[2]; u64 denominator = 0; /* gcc */ - struct pglist_data *pgdat = lruvec_pgdat(lruvec); unsigned long anon_prio, file_prio; enum scan_balance scan_balance; - unsigned long anon, file; unsigned long totalcost; unsigned long ap, fp; enum lru_list lru; @@ -2285,7 +2289,6 @@ static void get_scan_count(struct lruvec } scan_balance = SCAN_FRACT; - /* * Calculate the pressure balance between anon and file pages. * @@ -2300,30 +2303,12 @@ static void get_scan_count(struct lruvec anon_prio = swappiness; file_prio = 200 - anon_prio; - /* - * Because workloads change over time (and to avoid overflow) - * we keep these statistics as a floating average, which ends - * up weighing recent refaults more than old ones. - */ - - anon = lruvec_lru_size(lruvec, LRU_ACTIVE_ANON, MAX_NR_ZONES) + - lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, MAX_NR_ZONES); - file = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE, MAX_NR_ZONES) + - lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, MAX_NR_ZONES); - - spin_lock_irq(&pgdat->lru_lock); - totalcost = lruvec->anon_cost + lruvec->file_cost; - if (unlikely(totalcost > (anon + file) / 4)) { - lruvec->anon_cost /= 2; - lruvec->file_cost /= 2; - totalcost /= 2; - } + totalcost = sc->anon_cost + sc->file_cost; ap = anon_prio * (totalcost + 1); - ap /= lruvec->anon_cost + 1; + ap /= sc->anon_cost + 1; fp = file_prio * (totalcost + 1); - fp /= lruvec->file_cost + 1; - spin_unlock_irq(&pgdat->lru_lock); + fp /= sc->file_cost + 1; fraction[0] = ap; fraction[1] = fp; @@ -2688,6 +2673,14 @@ again: nr_scanned = sc->nr_scanned; /* + * Determine the scan balance between anon and file LRUs. + */ + spin_lock_irq(&pgdat->lru_lock); + sc->anon_cost = target_lruvec->anon_cost; + sc->file_cost = target_lruvec->file_cost; + spin_unlock_irq(&pgdat->lru_lock); + + /* * Target desirable inactive:active list ratios for the anon * and file LRU lists. */ _
