Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock
From: Roman Gushchin <hidden>
Date: 2021-10-01 23:52:22
Also in:
linux-mm, lkml
On Fri, Oct 01, 2021 at 03:09:36PM -0400, Waiman Long wrote:
When freeing a page associated with an offlined memcg, refill_stock() will put it into local stock delaying its demise until another memcg comes in to take its place in the stock. To avoid that, we now check for offlined memcg and go directly in this case to the slowpath for the uncharge via the repurposed cancel_charge() function.
Hi Waiman! I'm afraid it can make a cleanup of a dying cgroup slower: for every released page we'll potentially traverse the whole cgroup tree and decrease atomic page counters. I'm not sure I understand the benefits we get from this change which do justify the slowdown on the cleanup path. Thanks!
quoted hunk ↗ jump to hunk
Signed-off-by: Waiman Long <redacted> --- mm/memcontrol.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-)diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 4b32896d87a2..4568363062c1 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c@@ -2167,6 +2167,8 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages) return ret; } +static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages); + /* * Returns stocks cached in percpu and reset cached information. */@@ -2178,9 +2180,7 @@ static void drain_stock(struct memcg_stock_pcp *stock) return; if (stock->nr_pages) { - page_counter_uncharge(&old->memory, stock->nr_pages); - if (do_memsw_account()) - page_counter_uncharge(&old->memsw, stock->nr_pages); + cancel_charge(old, stock->nr_pages); stock->nr_pages = 0; }@@ -2219,6 +2219,14 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) struct memcg_stock_pcp *stock; unsigned long flags; + /* + * An offlined memcg shouldn't be put into stock. + */ + if (unlikely(memcg->kmem_state != KMEM_ONLINE)) { + cancel_charge(memcg, nr_pages); + return; + } + local_irq_save(flags); stock = this_cpu_ptr(&memcg_stock);@@ -2732,7 +2740,6 @@ static inline int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, return try_charge_memcg(memcg, gfp_mask, nr_pages); } -#if defined(CONFIG_MEMCG_KMEM) || defined(CONFIG_MMU) static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages) { if (mem_cgroup_is_root(memcg))@@ -2742,7 +2749,6 @@ static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages) if (do_memsw_account()) page_counter_uncharge(&memcg->memsw, nr_pages); } -#endif static void commit_charge(struct folio *folio, struct mem_cgroup *memcg) {-- 2.18.1