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Date: Sun, 18 Apr 2021 20:00:32 -0400 From: Waiman Long <longman@...hat.com> To: Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, Vladimir Davydov <vdavydov.dev@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Vlastimil Babka <vbabka@...e.cz>, Roman Gushchin <guro@...com> Cc: linux-kernel@...r.kernel.org, cgroups@...r.kernel.org, linux-mm@...ck.org, Shakeel Butt <shakeelb@...gle.com>, Muchun Song <songmuchun@...edance.com>, Alex Shi <alex.shi@...ux.alibaba.com>, Chris Down <chris@...isdown.name>, Yafang Shao <laoar.shao@...il.com>, Wei Yang <richard.weiyang@...il.com>, Masayoshi Mizuma <msys.mizuma@...il.com>, Xing Zhengjun <zhengjun.xing@...ux.intel.com>, Matthew Wilcox <willy@...radead.org>, Waiman Long <longman@...hat.com> Subject: [PATCH v4 5/5] mm/memcg: Improve refill_obj_stock() performance There are two issues with the current refill_obj_stock() code. First of all, when nr_bytes reaches over PAGE_SIZE, it calls drain_obj_stock() to atomically flush out remaining bytes to obj_cgroup, clear cached_objcg and do a obj_cgroup_put(). It is likely that the same obj_cgroup will be used again which leads to another call to drain_obj_stock() and obj_cgroup_get() as well as atomically retrieve the available byte from obj_cgroup. That is costly. Instead, we should just uncharge the excess pages, reduce the stock bytes and be done with it. The drain_obj_stock() function should only be called when obj_cgroup changes. Secondly, when charging an object of size not less than a page in obj_cgroup_charge(), it is possible that the remaining bytes to be refilled to the stock will overflow a page and cause refill_obj_stock() to uncharge 1 page. To avoid the additional uncharge in this case, a new overfill flag is added to refill_obj_stock() which will be set when called from obj_cgroup_charge(). Signed-off-by: Waiman Long <longman@...hat.com> --- mm/memcontrol.c | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index a6dd18f6d8a8..d13961352eef 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3357,23 +3357,34 @@ static bool obj_stock_flush_required(struct memcg_stock_pcp *stock, return false; } -static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes) +static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes, + bool overfill) { unsigned long flags; struct obj_stock *stock = get_obj_stock(&flags); + unsigned int nr_pages = 0; if (stock->cached_objcg != objcg) { /* reset if necessary */ - drain_obj_stock(stock); + if (stock->cached_objcg) + drain_obj_stock(stock); obj_cgroup_get(objcg); stock->cached_objcg = objcg; stock->nr_bytes = atomic_xchg(&objcg->nr_charged_bytes, 0); } stock->nr_bytes += nr_bytes; - if (stock->nr_bytes > PAGE_SIZE) - drain_obj_stock(stock); + if (!overfill && (stock->nr_bytes > PAGE_SIZE)) { + nr_pages = stock->nr_bytes >> PAGE_SHIFT; + stock->nr_bytes &= (PAGE_SIZE - 1); + } put_obj_stock(flags); + + if (nr_pages) { + rcu_read_lock(); + __memcg_kmem_uncharge(obj_cgroup_memcg(objcg), nr_pages); + rcu_read_unlock(); + } } int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size) @@ -3410,7 +3421,7 @@ int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size) ret = __memcg_kmem_charge(memcg, gfp, nr_pages); if (!ret && nr_bytes) - refill_obj_stock(objcg, PAGE_SIZE - nr_bytes); + refill_obj_stock(objcg, PAGE_SIZE - nr_bytes, true); css_put(&memcg->css); return ret; @@ -3418,7 +3429,7 @@ int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size) void obj_cgroup_uncharge(struct obj_cgroup *objcg, size_t size) { - refill_obj_stock(objcg, size); + refill_obj_stock(objcg, size, false); } #endif /* CONFIG_MEMCG_KMEM */ -- 2.18.1
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