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SubjectRe: [PATCH 2/4][mmotm] memcg: introduce charge-commit-cancel style of functions.
On Tue, 28 Oct 2008 19:11:25 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> There is a small race in do_swap_page(). When the page swapped-in is charged,
> the mapcount can be greater than 0. But, at the same time some process (shares
> it ) call unmap and make mapcount 1->0 and the page is uncharged.
>
> CPUA CPUB
> mapcount == 1.
> (1) charge if mapcount==0 zap_pte_range()
> (2) mapcount 1 => 0.
> (3) uncharge(). (success)
> (4) set page's rmap()
> mapcount 0=>1
>
> Then, this swap page's account is leaked.
>
> For fixing this, I added a new interface.
> - charge
> account to res_counter by PAGE_SIZE and try to free pages if necessary.
> - commit
> register page_cgroup and add to LRU if necessary.
> - cancel
> uncharge PAGE_SIZE because of do_swap_page failure.
>
>
> CPUA
> (1) charge (always)
> (2) set page's rmap (mapcount > 0)
> (3) commit charge was necessary or not after set_pte().
>
> This protocol uses PCG_USED bit on page_cgroup for avoiding over accounting.
> Usual mem_cgroup_charge_common() does charge -> commit at a time.
>
> And this patch also adds following function to clarify all charges.
>
> - mem_cgroup_newpage_charge() ....replacement for mem_cgroup_charge()
> called against newly allocated anon pages.
>
> - mem_cgroup_charge_migrate_fixup()
> called only from remove_migration_ptes().
> we'll have to rewrite this later.(this patch just keeps old behavior)
> This function will be removed by additional patch to make migration
> clearer.
>
> Good for clarify "what we does"
>
> Then, we have 4 following charge points.
> - newpage
> - swap-in
> - add-to-cache.
> - migration.
>
> Changelog v8 -> v9
> - fixed text
> Changelog v7 -> v8
> - handles that try_charge() sets NULL to *memcg.
>
> Changelog v5 -> v7:
> - added newpage_charge() and migrate_fixup().
> - renamed functions for swap-in from "swap" to "swapin"
> - add more precise description.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>
Looks good to me.

Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>


> include/linux/memcontrol.h | 35 +++++++++-
> mm/memcontrol.c | 155 ++++++++++++++++++++++++++++++++++++---------
> mm/memory.c | 12 ++-
> mm/migrate.c | 2
> mm/swapfile.c | 6 +
> 5 files changed, 169 insertions(+), 41 deletions(-)
>
> Index: mmotm-2.6.28rc2+/include/linux/memcontrol.h
> ===================================================================
> --- mmotm-2.6.28rc2+.orig/include/linux/memcontrol.h
> +++ mmotm-2.6.28rc2+/include/linux/memcontrol.h
> @@ -27,8 +27,17 @@ struct mm_struct;
>
> #ifdef CONFIG_CGROUP_MEM_RES_CTLR
>
> -extern int mem_cgroup_charge(struct page *page, struct mm_struct *mm,
> +extern int mem_cgroup_newpage_charge(struct page *page, struct mm_struct *mm,
> gfp_t gfp_mask);
> +extern int mem_cgroup_charge_migrate_fixup(struct page *page,
> + struct mm_struct *mm, gfp_t gfp_mask);
> +/* for swap handling */
> +extern int mem_cgroup_try_charge(struct mm_struct *mm,
> + gfp_t gfp_mask, struct mem_cgroup **ptr);
> +extern void mem_cgroup_commit_charge_swapin(struct page *page,
> + struct mem_cgroup *ptr);
> +extern void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *ptr);
> +
> extern int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
> gfp_t gfp_mask);
> extern void mem_cgroup_move_lists(struct page *page, enum lru_list lru);
> @@ -71,7 +80,9 @@ extern long mem_cgroup_calc_reclaim(stru
>
>
> #else /* CONFIG_CGROUP_MEM_RES_CTLR */
> -static inline int mem_cgroup_charge(struct page *page,
> +struct mem_cgroup;
> +
> +static inline int mem_cgroup_newpage_charge(struct page *page,
> struct mm_struct *mm, gfp_t gfp_mask)
> {
> return 0;
> @@ -83,6 +94,26 @@ static inline int mem_cgroup_cache_charg
> return 0;
> }
>
> +static inline int mem_cgroup_charge_migrate_fixup(struct page *page,
> + struct mm_struct *mm, gfp_t gfp_mask)
> +{
> + return 0;
> +}
> +
> +static int mem_cgroup_try_charge(struct mm_struct *mm,
> + gfp_t gfp_mask, struct mem_cgroup **ptr)
> +{
> + return 0;
> +}
> +
> +static void mem_cgroup_commit_charge_swapin(struct page *page,
> + struct mem_cgroup *ptr)
> +{
> +}
> +static void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *ptr)
> +{
> +}
> +
> static inline void mem_cgroup_uncharge_page(struct page *page)
> {
> }
> Index: mmotm-2.6.28rc2+/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.28rc2+.orig/mm/memcontrol.c
> +++ mmotm-2.6.28rc2+/mm/memcontrol.c
> @@ -467,35 +467,31 @@ unsigned long mem_cgroup_isolate_pages(u
> return nr_taken;
> }
>
> -/*
> - * Charge the memory controller for page usage.
> - * Return
> - * 0 if the charge was successful
> - * < 0 if the cgroup is over its limit
> +
> +/**
> + * mem_cgroup_try_charge - get charge of PAGE_SIZE.
> + * @mm: an mm_struct which is charged against. (when *memcg is NULL)
> + * @gfp_mask: gfp_mask for reclaim.
> + * @memcg: a pointer to memory cgroup which is charged against.
> + *
> + * charge against memory cgroup pointed by *memcg. if *memcg == NULL, estimated
> + * memory cgroup from @mm is got and stored in *memcg.
> + *
> + * Returns 0 if success. -ENOMEM at failure.
> */
> -static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
> - gfp_t gfp_mask, enum charge_type ctype,
> - struct mem_cgroup *memcg)
> +
> +int mem_cgroup_try_charge(struct mm_struct *mm,
> + gfp_t gfp_mask, struct mem_cgroup **memcg)
> {
> struct mem_cgroup *mem;
> - struct page_cgroup *pc;
> - unsigned long nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> - struct mem_cgroup_per_zone *mz;
> - unsigned long flags;
> -
> - pc = lookup_page_cgroup(page);
> - /* can happen at boot */
> - if (unlikely(!pc))
> - return 0;
> - prefetchw(pc);
> + int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> /*
> * We always charge the cgroup the mm_struct belongs to.
> * The mm_struct's mem_cgroup changes on task migration if the
> * thread group leader migrates. It's possible that mm is not
> * set, if so charge the init_mm (happens for pagecache usage).
> */
> -
> - if (likely(!memcg)) {
> + if (likely(!*memcg)) {
> rcu_read_lock();
> mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
> if (unlikely(!mem)) {
> @@ -506,15 +502,17 @@ static int mem_cgroup_charge_common(stru
> * For every charge from the cgroup, increment reference count
> */
> css_get(&mem->css);
> + *memcg = mem;
> rcu_read_unlock();
> } else {
> - mem = memcg;
> - css_get(&memcg->css);
> + mem = *memcg;
> + css_get(&mem->css);
> }
>
> +
> while (unlikely(res_counter_charge(&mem->res, PAGE_SIZE))) {
> if (!(gfp_mask & __GFP_WAIT))
> - goto out;
> + goto nomem;
>
> if (try_to_free_mem_cgroup_pages(mem, gfp_mask))
> continue;
> @@ -531,18 +529,37 @@ static int mem_cgroup_charge_common(stru
>
> if (!nr_retries--) {
> mem_cgroup_out_of_memory(mem, gfp_mask);
> - goto out;
> + goto nomem;
> }
> }
> + return 0;
> +nomem:
> + css_put(&mem->css);
> + return -ENOMEM;
> +}
> +
> +/*
> + * commit a charge got by mem_cgroup_try_charge() and makes page_cgroup to be
> + * USED state. If already USED, uncharge and return.
> + */
>
> +static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
> + struct page_cgroup *pc,
> + enum charge_type ctype)
> +{
> + struct mem_cgroup_per_zone *mz;
> + unsigned long flags;
> +
> + /* try_charge() can return NULL to *memcg, taking care of it. */
> + if (!mem)
> + return;
>
> lock_page_cgroup(pc);
> if (unlikely(PageCgroupUsed(pc))) {
> unlock_page_cgroup(pc);
> res_counter_uncharge(&mem->res, PAGE_SIZE);
> css_put(&mem->css);
> -
> - goto done;
> + return;
> }
> pc->mem_cgroup = mem;
> /*
> @@ -557,15 +574,39 @@ static int mem_cgroup_charge_common(stru
> __mem_cgroup_add_list(mz, pc);
> spin_unlock_irqrestore(&mz->lru_lock, flags);
> unlock_page_cgroup(pc);
> +}
> +
> +/*
> + * Charge the memory controller for page usage.
> + * Return
> + * 0 if the charge was successful
> + * < 0 if the cgroup is over its limit
> + */
> +static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
> + gfp_t gfp_mask, enum charge_type ctype,
> + struct mem_cgroup *memcg)
> +{
> + struct mem_cgroup *mem;
> + struct page_cgroup *pc;
> + int ret;
>
> -done:
> + pc = lookup_page_cgroup(page);
> + /* can happen at boot */
> + if (unlikely(!pc))
> + return 0;
> + prefetchw(pc);
> +
> + mem = memcg;
> + ret = mem_cgroup_try_charge(mm, gfp_mask, &mem);
> + if (ret)
> + return ret;
> +
> + __mem_cgroup_commit_charge(mem, pc, ctype);
> return 0;
> -out:
> - css_put(&mem->css);
> - return -ENOMEM;
> }
>
> -int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask)
> +int mem_cgroup_newpage_charge(struct page *page,
> + struct mm_struct *mm, gfp_t gfp_mask)
> {
> if (mem_cgroup_subsys.disabled)
> return 0;
> @@ -586,6 +627,34 @@ int mem_cgroup_charge(struct page *page,
> MEM_CGROUP_CHARGE_TYPE_MAPPED, NULL);
> }
>
> +/*
> + * same as mem_cgroup_newpage_charge(), now.
> + * But what we assume is different from newpage, and this is special case.
> + * treat this in special function. easy for maintenance.
> + */
> +
> +int mem_cgroup_charge_migrate_fixup(struct page *page,
> + struct mm_struct *mm, gfp_t gfp_mask)
> +{
> + if (mem_cgroup_subsys.disabled)
> + return 0;
> +
> + if (PageCompound(page))
> + return 0;
> +
> + if (page_mapped(page) || (page->mapping && !PageAnon(page)))
> + return 0;
> +
> + if (unlikely(!mm))
> + mm = &init_mm;
> +
> + return mem_cgroup_charge_common(page, mm, gfp_mask,
> + MEM_CGROUP_CHARGE_TYPE_MAPPED, NULL);
> +}
> +
> +
> +
> +
> int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
> gfp_t gfp_mask)
> {
> @@ -628,6 +697,30 @@ int mem_cgroup_cache_charge(struct page
> MEM_CGROUP_CHARGE_TYPE_SHMEM, NULL);
> }
>
> +
> +void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
> +{
> + struct page_cgroup *pc;
> +
> + if (mem_cgroup_subsys.disabled)
> + return;
> + if (!ptr)
> + return;
> + pc = lookup_page_cgroup(page);
> + __mem_cgroup_commit_charge(ptr, pc, MEM_CGROUP_CHARGE_TYPE_MAPPED);
> +}
> +
> +void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *mem)
> +{
> + if (mem_cgroup_subsys.disabled)
> + return;
> + if (!mem)
> + return;
> + res_counter_uncharge(&mem->res, PAGE_SIZE);
> + css_put(&mem->css);
> +}
> +
> +
> /*
> * uncharge if !page_mapped(page)
> */
> Index: mmotm-2.6.28rc2+/mm/memory.c
> ===================================================================
> --- mmotm-2.6.28rc2+.orig/mm/memory.c
> +++ mmotm-2.6.28rc2+/mm/memory.c
> @@ -1889,7 +1889,7 @@ gotten:
> cow_user_page(new_page, old_page, address, vma);
> __SetPageUptodate(new_page);
>
> - if (mem_cgroup_charge(new_page, mm, GFP_KERNEL))
> + if (mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))
> goto oom_free_new;
>
> /*
> @@ -2285,6 +2285,7 @@ static int do_swap_page(struct mm_struct
> struct page *page;
> swp_entry_t entry;
> pte_t pte;
> + struct mem_cgroup *ptr = NULL;
> int ret = 0;
>
> if (!pte_unmap_same(mm, pmd, page_table, orig_pte))
> @@ -2323,7 +2324,7 @@ static int do_swap_page(struct mm_struct
> lock_page(page);
> delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
>
> - if (mem_cgroup_charge(page, mm, GFP_KERNEL)) {
> + if (mem_cgroup_try_charge(mm, GFP_KERNEL, &ptr) == -ENOMEM) {
> ret = VM_FAULT_OOM;
> unlock_page(page);
> goto out;
> @@ -2353,6 +2354,7 @@ static int do_swap_page(struct mm_struct
> flush_icache_page(vma, page);
> set_pte_at(mm, address, page_table, pte);
> page_add_anon_rmap(page, vma, address);
> + mem_cgroup_commit_charge_swapin(page, ptr);
>
> swap_free(entry);
> if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page))
> @@ -2373,7 +2375,7 @@ unlock:
> out:
> return ret;
> out_nomap:
> - mem_cgroup_uncharge_page(page);
> + mem_cgroup_cancel_charge_swapin(ptr);
> pte_unmap_unlock(page_table, ptl);
> unlock_page(page);
> page_cache_release(page);
> @@ -2403,7 +2405,7 @@ static int do_anonymous_page(struct mm_s
> goto oom;
> __SetPageUptodate(page);
>
> - if (mem_cgroup_charge(page, mm, GFP_KERNEL))
> + if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL))
> goto oom_free_page;
>
> entry = mk_pte(page, vma->vm_page_prot);
> @@ -2496,7 +2498,7 @@ static int __do_fault(struct mm_struct *
> ret = VM_FAULT_OOM;
> goto out;
> }
> - if (mem_cgroup_charge(page, mm, GFP_KERNEL)) {
> + if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) {
> ret = VM_FAULT_OOM;
> page_cache_release(page);
> goto out;
> Index: mmotm-2.6.28rc2+/mm/migrate.c
> ===================================================================
> --- mmotm-2.6.28rc2+.orig/mm/migrate.c
> +++ mmotm-2.6.28rc2+/mm/migrate.c
> @@ -133,7 +133,7 @@ static void remove_migration_pte(struct
> * be reliable, and this charge can actually fail: oh well, we don't
> * make the situation any worse by proceeding as if it had succeeded.
> */
> - mem_cgroup_charge(new, mm, GFP_ATOMIC);
> + mem_cgroup_charge_migrate_fixup(new, mm, GFP_ATOMIC);
>
> get_page(new);
> pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
> Index: mmotm-2.6.28rc2+/mm/swapfile.c
> ===================================================================
> --- mmotm-2.6.28rc2+.orig/mm/swapfile.c
> +++ mmotm-2.6.28rc2+/mm/swapfile.c
> @@ -530,17 +530,18 @@ unsigned int count_swap_pages(int type,
> static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
> unsigned long addr, swp_entry_t entry, struct page *page)
> {
> + struct mem_cgroup *ptr = NULL;
> spinlock_t *ptl;
> pte_t *pte;
> int ret = 1;
>
> - if (mem_cgroup_charge(page, vma->vm_mm, GFP_KERNEL))
> + if (mem_cgroup_try_charge(vma->vm_mm, GFP_KERNEL, &ptr))
> ret = -ENOMEM;
>
> pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) {
> if (ret > 0)
> - mem_cgroup_uncharge_page(page);
> + mem_cgroup_cancel_charge_swapin(ptr);
> ret = 0;
> goto out;
> }
> @@ -550,6 +551,7 @@ static int unuse_pte(struct vm_area_stru
> set_pte_at(vma->vm_mm, addr, pte,
> pte_mkold(mk_pte(page, vma->vm_page_prot)));
> page_add_anon_rmap(page, vma, addr);
> + mem_cgroup_commit_charge_swapin(page, ptr);
> swap_free(entry);
> /*
> * Move the page to the active list so it is not
>


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