From: Jakub Kicinski <kuba@xxxxxxxxxx> Subject: mm/memcg: prepare for swap over-high accounting and penalty calculation Patch series "memcg: Slow down swap allocation as the available space gets depleted", v6. Tejun describes the problem as follows: When swap runs out, there's an abrupt change in system behavior - the anonymous memory suddenly becomes unmanageable which readily breaks any sort of memory isolation and can bring down the whole system. To avoid that, oomd [1] monitors free swap space and triggers kills when it drops below the specific threshold (e.g. 15%). While this works, it's far from ideal: - Depending on IO performance and total swap size, a given headroom might not be enough or too much. - oomd has to monitor swap depletion in addition to the usual pressure metrics and it currently doesn't consider memory.swap.max. Solve this by adapting parts of the approach that memory.high uses - slow down allocation as the resource gets depleted turning the depletion behavior from abrupt cliff one to gradual degradation observable through memory pressure metric. [1] https://github.com/facebookincubator/oomd This patch (of 4): Slice the memory overage calculation logic a little bit so we can reuse it to apply a similar penalty to the swap. The logic which accesses the memory-specific fields (use and high values) has to be taken out of calculate_high_delay(). Link: http://lkml.kernel.org/r/20200527195846.102707-1-kuba@xxxxxxxxxx Link: http://lkml.kernel.org/r/20200527195846.102707-2-kuba@xxxxxxxxxx Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Chris Down <chris@xxxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/memcontrol.c | 62 +++++++++++++++++++++++++--------------------- 1 file changed, 35 insertions(+), 27 deletions(-) --- a/mm/memcontrol.c~mm-prepare-for-swap-over-high-accounting-and-penalty-calculation +++ a/mm/memcontrol.c @@ -2321,41 +2321,48 @@ static void high_work_func(struct work_s #define MEMCG_DELAY_PRECISION_SHIFT 20 #define MEMCG_DELAY_SCALING_SHIFT 14 -/* - * Get the number of jiffies that we should penalise a mischievous cgroup which - * is exceeding its memory.high by checking both it and its ancestors. - */ -static unsigned long calculate_high_delay(struct mem_cgroup *memcg, - unsigned int nr_pages) +static u64 calculate_overage(unsigned long usage, unsigned long high) { - unsigned long penalty_jiffies; - u64 max_overage = 0; + u64 overage; - do { - unsigned long usage, high; - u64 overage; + if (usage <= high) + return 0; - usage = page_counter_read(&memcg->memory); - high = READ_ONCE(memcg->high); + /* + * Prevent division by 0 in overage calculation by acting as if + * it was a threshold of 1 page + */ + high = max(high, 1UL); - if (usage <= high) - continue; + overage = usage - high; + overage <<= MEMCG_DELAY_PRECISION_SHIFT; + return div64_u64(overage, high); +} - /* - * Prevent division by 0 in overage calculation by acting as if - * it was a threshold of 1 page - */ - high = max(high, 1UL); - - overage = usage - high; - overage <<= MEMCG_DELAY_PRECISION_SHIFT; - overage = div64_u64(overage, high); +static u64 mem_find_max_overage(struct mem_cgroup *memcg) +{ + u64 overage, max_overage = 0; - if (overage > max_overage) - max_overage = overage; + do { + overage = calculate_overage(page_counter_read(&memcg->memory), + READ_ONCE(memcg->high)); + max_overage = max(overage, max_overage); } while ((memcg = parent_mem_cgroup(memcg)) && !mem_cgroup_is_root(memcg)); + return max_overage; +} + +/* + * Get the number of jiffies that we should penalise a mischievous cgroup which + * is exceeding its memory.high by checking both it and its ancestors. + */ +static unsigned long calculate_high_delay(struct mem_cgroup *memcg, + unsigned int nr_pages, + u64 max_overage) +{ + unsigned long penalty_jiffies; + if (!max_overage) return 0; @@ -2411,7 +2418,8 @@ void mem_cgroup_handle_over_high(void) * memory.high is breached and reclaim is unable to keep up. Throttle * allocators proactively to slow down excessive growth. */ - penalty_jiffies = calculate_high_delay(memcg, nr_pages); + penalty_jiffies = calculate_high_delay(memcg, nr_pages, + mem_find_max_overage(memcg)); /* * Don't sleep if the amount of jiffies this memcg owes us is so low _
