From a3b2d692690aef228e493b1beaafe5364cab3237 Mon Sep 17 00:00:00 2001 From: KAMEZAWA Hiroyuki Date: Thu, 2 Apr 2009 16:57:45 -0700 Subject: cgroups: use css id in swap cgroup for saving memory v5 Try to use CSS ID for records in swap_cgroup. By this, on 64bit machine, size of swap_cgroup goes down to 2 bytes from 8bytes. This means, when 2GB of swap is equipped, (assume the page size is 4096bytes) From size of swap_cgroup = 2G/4k * 8 = 4Mbytes. To size of swap_cgroup = 2G/4k * 2 = 1Mbytes. Reduction is large. Of course, there are trade-offs. This CSS ID will add overhead to swap-in/swap-out/swap-free. But in general, - swap is a resource which the user tend to avoid use. - If swap is never used, swap_cgroup area is not used. - Reading traditional manuals, size of swap should be proportional to size of memory. Memory size of machine is increasing now. I think reducing size of swap_cgroup makes sense. Note: - ID->CSS lookup routine has no locks, it's under RCU-Read-Side. - memcg can be obsolete at rmdir() but not freed while refcnt from swap_cgroup is available. Changelog v4->v5: - reworked on to memcg-charge-swapcache-to-proper-memcg.patch Changlog ->v4: - fixed not configured case. - deleted unnecessary comments. - fixed NULL pointer bug. - fixed message in dmesg. [nishimura@mxp.nes.nec.co.jp: css_tryget can be called twice in !PageCgroupUsed case] Signed-off-by: KAMEZAWA Hiroyuki Cc: Li Zefan Cc: Balbir Singh Cc: Paul Menage Cc: Hugh Dickins Signed-off-by: Daisuke Nishimura Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memcontrol.c | 74 +++++++++++++++++++++++++++++++++++++++++++++++---------- 1 file changed, 62 insertions(+), 12 deletions(-) (limited to 'mm/memcontrol.c') diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 81b0ae8183d0..55dea5968464 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -991,10 +991,31 @@ nomem: return -ENOMEM; } + +/* + * A helper function to get mem_cgroup from ID. must be called under + * rcu_read_lock(). The caller must check css_is_removed() or some if + * it's concern. (dropping refcnt from swap can be called against removed + * memcg.) + */ +static struct mem_cgroup *mem_cgroup_lookup(unsigned short id) +{ + struct cgroup_subsys_state *css; + + /* ID 0 is unused ID */ + if (!id) + return NULL; + css = css_lookup(&mem_cgroup_subsys, id); + if (!css) + return NULL; + return container_of(css, struct mem_cgroup, css); +} + static struct mem_cgroup *try_get_mem_cgroup_from_swapcache(struct page *page) { struct mem_cgroup *mem; struct page_cgroup *pc; + unsigned short id; swp_entry_t ent; VM_BUG_ON(!PageLocked(page)); @@ -1006,16 +1027,19 @@ static struct mem_cgroup *try_get_mem_cgroup_from_swapcache(struct page *page) /* * Used bit of swapcache is solid under page lock. */ - if (PageCgroupUsed(pc)) + if (PageCgroupUsed(pc)) { mem = pc->mem_cgroup; - else { + if (mem && !css_tryget(&mem->css)) + mem = NULL; + } else { ent.val = page_private(page); - mem = lookup_swap_cgroup(ent); + id = lookup_swap_cgroup(ent); + rcu_read_lock(); + mem = mem_cgroup_lookup(id); + if (mem && !css_tryget(&mem->css)) + mem = NULL; + rcu_read_unlock(); } - if (!mem) - return NULL; - if (!css_tryget(&mem->css)) - return NULL; return mem; } @@ -1276,12 +1300,22 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm, if (do_swap_account && !ret && PageSwapCache(page)) { swp_entry_t ent = {.val = page_private(page)}; + unsigned short id; /* avoid double counting */ - mem = swap_cgroup_record(ent, NULL); + id = swap_cgroup_record(ent, 0); + rcu_read_lock(); + mem = mem_cgroup_lookup(id); if (mem) { + /* + * We did swap-in. Then, this entry is doubly counted + * both in mem and memsw. We uncharge it, here. + * Recorded ID can be obsolete. We avoid calling + * css_tryget() + */ res_counter_uncharge(&mem->memsw, PAGE_SIZE); mem_cgroup_put(mem); } + rcu_read_unlock(); } return ret; } @@ -1346,13 +1380,21 @@ void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr) */ if (do_swap_account && PageSwapCache(page)) { swp_entry_t ent = {.val = page_private(page)}; + unsigned short id; struct mem_cgroup *memcg; - memcg = swap_cgroup_record(ent, NULL); + + id = swap_cgroup_record(ent, 0); + rcu_read_lock(); + memcg = mem_cgroup_lookup(id); if (memcg) { + /* + * This recorded memcg can be obsolete one. So, avoid + * calling css_tryget + */ res_counter_uncharge(&memcg->memsw, PAGE_SIZE); mem_cgroup_put(memcg); } - + rcu_read_unlock(); } /* add this page(page_cgroup) to the LRU we want. */ @@ -1473,7 +1515,7 @@ void mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent) MEM_CGROUP_CHARGE_TYPE_SWAPOUT); /* record memcg information */ if (do_swap_account && memcg) { - swap_cgroup_record(ent, memcg); + swap_cgroup_record(ent, css_id(&memcg->css)); mem_cgroup_get(memcg); } if (memcg) @@ -1488,15 +1530,23 @@ void mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent) void mem_cgroup_uncharge_swap(swp_entry_t ent) { struct mem_cgroup *memcg; + unsigned short id; if (!do_swap_account) return; - memcg = swap_cgroup_record(ent, NULL); + id = swap_cgroup_record(ent, 0); + rcu_read_lock(); + memcg = mem_cgroup_lookup(id); if (memcg) { + /* + * We uncharge this because swap is freed. + * This memcg can be obsolete one. We avoid calling css_tryget + */ res_counter_uncharge(&memcg->memsw, PAGE_SIZE); mem_cgroup_put(memcg); } + rcu_read_unlock(); } #endif -- cgit v1.2.3