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Date: Wed, 22 Oct 2014 10:54:59 +0900
From: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Johannes Weiner <hannes@...xchg.org>,
Andrew Morton <akpm@...ux-foundation.org>
CC: Hugh Dickins <hughd@...gle.com>, Michal Hocko <mhocko@...e.cz>,
Vladimir Davydov <vdavydov@...allels.com>,
<linux-mm@...ck.org>, <cgroups@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [patch 4/4] mm: memcontrol: remove unnecessary PCG_USED pc->mem_cgroup
valid flag
(2014/10/21 0:22), Johannes Weiner wrote:
> pc->mem_cgroup had to be left intact after uncharge for the final LRU
> removal, and !PCG_USED indicated whether the page was uncharged. But
> since 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API") pages are
> uncharged after the final LRU removal. Uncharge can simply clear the
> pointer and the PCG_USED/PageCgroupUsed sites can test that instead.
>
> Because this is the last page_cgroup flag, this patch reduces the
> memcg per-page overhead to a single pointer.
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
awesome.
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
> include/linux/page_cgroup.h | 10 -----
> mm/memcontrol.c | 107 +++++++++++++++++---------------------------
> 2 files changed, 42 insertions(+), 75 deletions(-)
>
> diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
> index 97536e685843..1289be6b436c 100644
> --- a/include/linux/page_cgroup.h
> +++ b/include/linux/page_cgroup.h
> @@ -1,11 +1,6 @@
> #ifndef __LINUX_PAGE_CGROUP_H
> #define __LINUX_PAGE_CGROUP_H
>
> -enum {
> - /* flags for mem_cgroup */
> - PCG_USED = 0x01, /* This page is charged to a memcg */
> -};
> -
> struct pglist_data;
>
> #ifdef CONFIG_MEMCG
> @@ -19,7 +14,6 @@ struct mem_cgroup;
> * then the page cgroup for pfn always exists.
> */
> struct page_cgroup {
> - unsigned long flags;
> struct mem_cgroup *mem_cgroup;
> };
>
> @@ -39,10 +33,6 @@ static inline void page_cgroup_init(void)
>
> struct page_cgroup *lookup_page_cgroup(struct page *page);
>
> -static inline int PageCgroupUsed(struct page_cgroup *pc)
> -{
> - return !!(pc->flags & PCG_USED);
> -}
> #else /* !CONFIG_MEMCG */
> struct page_cgroup;
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 1d66ac49e702..48d49c6b08d1 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1284,14 +1284,12 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct zone *zone)
>
> pc = lookup_page_cgroup(page);
> memcg = pc->mem_cgroup;
> -
> /*
> * Swapcache readahead pages are added to the LRU - and
> - * possibly migrated - before they are charged. Ensure
> - * pc->mem_cgroup is sane.
> + * possibly migrated - before they are charged.
> */
> - if (!PageLRU(page) && !PageCgroupUsed(pc) && memcg != root_mem_cgroup)
> - pc->mem_cgroup = memcg = root_mem_cgroup;
> + if (!memcg)
> + memcg = root_mem_cgroup;
>
> mz = mem_cgroup_page_zoneinfo(memcg, page);
> lruvec = &mz->lruvec;
> @@ -2141,7 +2139,7 @@ void __mem_cgroup_begin_update_page_stat(struct page *page,
> pc = lookup_page_cgroup(page);
> again:
> memcg = pc->mem_cgroup;
> - if (unlikely(!memcg || !PageCgroupUsed(pc)))
> + if (unlikely(!memcg))
> return;
> /*
> * If this memory cgroup is not under account moving, we don't
> @@ -2154,7 +2152,7 @@ again:
> return;
>
> move_lock_mem_cgroup(memcg, flags);
> - if (memcg != pc->mem_cgroup || !PageCgroupUsed(pc)) {
> + if (memcg != pc->mem_cgroup) {
> move_unlock_mem_cgroup(memcg, flags);
> goto again;
> }
> @@ -2186,7 +2184,7 @@ void mem_cgroup_update_page_stat(struct page *page,
>
> pc = lookup_page_cgroup(page);
> memcg = pc->mem_cgroup;
> - if (unlikely(!memcg || !PageCgroupUsed(pc)))
> + if (unlikely(!memcg))
> return;
>
> this_cpu_add(memcg->stat->count[idx], val);
> @@ -2525,9 +2523,10 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
> VM_BUG_ON_PAGE(!PageLocked(page), page);
>
> pc = lookup_page_cgroup(page);
> - if (PageCgroupUsed(pc)) {
> - memcg = pc->mem_cgroup;
> - if (memcg && !css_tryget_online(&memcg->css))
> + memcg = pc->mem_cgroup;
> +
> + if (memcg) {
> + if (!css_tryget_online(&memcg->css))
> memcg = NULL;
> } else if (PageSwapCache(page)) {
> ent.val = page_private(page);
> @@ -2578,7 +2577,7 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg,
> struct page_cgroup *pc = lookup_page_cgroup(page);
> int isolated;
>
> - VM_BUG_ON_PAGE(PageCgroupUsed(pc), page);
> + VM_BUG_ON_PAGE(pc->mem_cgroup, page);
> /*
> * we don't need page_cgroup_lock about tail pages, becase they are not
> * accessed by any other context at this point.
> @@ -2593,7 +2592,7 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg,
>
> /*
> * Nobody should be changing or seriously looking at
> - * pc->mem_cgroup and pc->flags at this point:
> + * pc->mem_cgroup at this point:
> *
> * - the page is uncharged
> *
> @@ -2606,7 +2605,6 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg,
> * have the page locked
> */
> pc->mem_cgroup = memcg;
> - pc->flags = PCG_USED;
>
> if (lrucare)
> unlock_page_lru(page, isolated);
> @@ -3120,37 +3118,22 @@ void __memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg,
> memcg_uncharge_kmem(memcg, 1 << order);
> return;
> }
> - /*
> - * The page is freshly allocated and not visible to any
> - * outside callers yet. Set up pc non-atomically.
> - */
> pc = lookup_page_cgroup(page);
> pc->mem_cgroup = memcg;
> - pc->flags = PCG_USED;
> }
>
> void __memcg_kmem_uncharge_pages(struct page *page, int order)
> {
> - struct mem_cgroup *memcg = NULL;
> - struct page_cgroup *pc;
> -
> -
> - pc = lookup_page_cgroup(page);
> - if (!PageCgroupUsed(pc))
> - return;
> -
> - memcg = pc->mem_cgroup;
> - pc->flags = 0;
> + struct page_cgroup *pc = lookup_page_cgroup(page);
> + struct mem_cgroup *memcg = pc->mem_cgroup;
>
> - /*
> - * We trust that only if there is a memcg associated with the page, it
> - * is a valid allocation
> - */
> if (!memcg)
> return;
>
> VM_BUG_ON_PAGE(mem_cgroup_is_root(memcg), page);
> +
> memcg_uncharge_kmem(memcg, 1 << order);
> + pc->mem_cgroup = NULL;
> }
> #else
> static inline void memcg_unregister_all_caches(struct mem_cgroup *memcg)
> @@ -3168,21 +3151,16 @@ static inline void memcg_unregister_all_caches(struct mem_cgroup *memcg)
> */
> void mem_cgroup_split_huge_fixup(struct page *head)
> {
> - struct page_cgroup *head_pc = lookup_page_cgroup(head);
> - struct page_cgroup *pc;
> - struct mem_cgroup *memcg;
> + struct page_cgroup *pc = lookup_page_cgroup(head);
> int i;
>
> if (mem_cgroup_disabled())
> return;
>
> - memcg = head_pc->mem_cgroup;
> - for (i = 1; i < HPAGE_PMD_NR; i++) {
> - pc = head_pc + i;
> - pc->mem_cgroup = memcg;
> - pc->flags = head_pc->flags;
> - }
> - __this_cpu_sub(memcg->stat->count[MEM_CGROUP_STAT_RSS_HUGE],
> + for (i = 1; i < HPAGE_PMD_NR; i++)
> + pc[i].mem_cgroup = pc[0].mem_cgroup;
> +
> + __this_cpu_sub(pc[0].mem_cgroup->stat->count[MEM_CGROUP_STAT_RSS_HUGE],
> HPAGE_PMD_NR);
> }
> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> @@ -3232,7 +3210,7 @@ static int mem_cgroup_move_account(struct page *page,
> goto out;
>
> ret = -EINVAL;
> - if (!PageCgroupUsed(pc) || pc->mem_cgroup != from)
> + if (pc->mem_cgroup != from)
> goto out_unlock;
>
> move_lock_mem_cgroup(from, &flags);
> @@ -3342,7 +3320,7 @@ static struct page_cgroup *lookup_page_cgroup_used(struct page *page)
> * the first time, i.e. during boot or memory hotplug;
> * or when mem_cgroup_disabled().
> */
> - if (likely(pc) && PageCgroupUsed(pc))
> + if (likely(pc) && pc->mem_cgroup)
> return pc;
> return NULL;
> }
> @@ -3360,10 +3338,8 @@ void mem_cgroup_print_bad_page(struct page *page)
> struct page_cgroup *pc;
>
> pc = lookup_page_cgroup_used(page);
> - if (pc) {
> - pr_alert("pc:%p pc->flags:%lx pc->mem_cgroup:%p\n",
> - pc, pc->flags, pc->mem_cgroup);
> - }
> + if (pc)
> + pr_alert("pc:%p pc->mem_cgroup:%p\n", pc, pc->mem_cgroup);
> }
> #endif
>
> @@ -5330,7 +5306,7 @@ static enum mc_target_type get_mctgt_type(struct vm_area_struct *vma,
> * mem_cgroup_move_account() checks the pc is valid or
> * not under LRU exclusion.
> */
> - if (PageCgroupUsed(pc) && pc->mem_cgroup == mc.from) {
> + if (pc->mem_cgroup == mc.from) {
> ret = MC_TARGET_PAGE;
> if (target)
> target->page = page;
> @@ -5366,7 +5342,7 @@ static enum mc_target_type get_mctgt_type_thp(struct vm_area_struct *vma,
> if (!move_anon())
> return ret;
> pc = lookup_page_cgroup(page);
> - if (PageCgroupUsed(pc) && pc->mem_cgroup == mc.from) {
> + if (pc->mem_cgroup == mc.from) {
> ret = MC_TARGET_PAGE;
> if (target) {
> get_page(page);
> @@ -5810,18 +5786,17 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
> return;
>
> pc = lookup_page_cgroup(page);
> + memcg = pc->mem_cgroup;
>
> /* Readahead page, never charged */
> - if (!PageCgroupUsed(pc))
> + if (!memcg)
> return;
>
> - memcg = pc->mem_cgroup;
> -
> oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg));
> VM_BUG_ON_PAGE(oldid, page);
> mem_cgroup_swap_statistics(memcg, true);
>
> - pc->flags = 0;
> + pc->mem_cgroup = NULL;
>
> if (!mem_cgroup_is_root(memcg))
> page_counter_uncharge(&memcg->memory, 1);
> @@ -5895,7 +5870,7 @@ int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
> * the page lock, which serializes swap cache removal, which
> * in turn serializes uncharging.
> */
> - if (PageCgroupUsed(pc))
> + if (pc->mem_cgroup)
> goto out;
> }
>
> @@ -6057,13 +6032,13 @@ static void uncharge_list(struct list_head *page_list)
> VM_BUG_ON_PAGE(page_count(page), page);
>
> pc = lookup_page_cgroup(page);
> - if (!PageCgroupUsed(pc))
> + if (!pc->mem_cgroup)
> continue;
>
> /*
> * Nobody should be changing or seriously looking at
> - * pc->mem_cgroup and pc->flags at this point, we have
> - * fully exclusive access to the page.
> + * pc->mem_cgroup at this point, we have fully
> + * exclusive access to the page.
> */
>
> if (memcg != pc->mem_cgroup) {
> @@ -6086,7 +6061,7 @@ static void uncharge_list(struct list_head *page_list)
> else
> nr_file += nr_pages;
>
> - pc->flags = 0;
> + pc->mem_cgroup = NULL;
>
> pgpgout++;
> } while (next != page_list);
> @@ -6112,7 +6087,7 @@ void mem_cgroup_uncharge(struct page *page)
>
> /* Don't touch page->lru of any random page, pre-check: */
> pc = lookup_page_cgroup(page);
> - if (!PageCgroupUsed(pc))
> + if (!pc->mem_cgroup)
> return;
>
> INIT_LIST_HEAD(&page->lru);
> @@ -6148,6 +6123,7 @@ void mem_cgroup_uncharge_list(struct list_head *page_list)
> void mem_cgroup_migrate(struct page *oldpage, struct page *newpage,
> bool lrucare)
> {
> + struct mem_cgroup *memcg;
> struct page_cgroup *pc;
> int isolated;
>
> @@ -6164,7 +6140,7 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage,
>
> /* Page cache replacement: new page already charged? */
> pc = lookup_page_cgroup(newpage);
> - if (PageCgroupUsed(pc))
> + if (pc->mem_cgroup)
> return;
>
> /*
> @@ -6174,18 +6150,19 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage,
> * reclaim just put back on the LRU but has not released yet.
> */
> pc = lookup_page_cgroup(oldpage);
> - if (!PageCgroupUsed(pc))
> + memcg = pc->mem_cgroup;
> + if (!memcg)
> return;
>
> if (lrucare)
> lock_page_lru(oldpage, &isolated);
>
> - pc->flags = 0;
> + pc->mem_cgroup = NULL;
>
> if (lrucare)
> unlock_page_lru(oldpage, isolated);
>
> - commit_charge(newpage, pc->mem_cgroup, lrucare);
> + commit_charge(newpage, memcg, lrucare);
> }
>
> /*
>
--
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