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Message-Id: <20110309150750.d570798c.kamezawa.hiroyu@jp.fujitsu.com>
Date: Wed, 9 Mar 2011 15:07:50 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2] memcg: fix leak on wrong LRU with FUSE
On Tue, 8 Mar 2011 18:18:32 +0900
Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:
> On Tue, 8 Mar 2011 13:56:12 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
>
> > fs/fuse/dev.c::fuse_try_move_page() does
> >
> > (1) remove a page by ->steal()
> > (2) re-add the page to page cache
> > (3) link the page to LRU if it was not on LRU at (1)
> >
> > This implies the page is _on_ LRU when it's added to radix-tree.
> > So, the page is added to memory cgroup while it's on LRU.
> > because LRU is lazy and no one flushs it.
> >
> > This is the same behavior as SwapCache and needs special care as
> > - remove page from LRU before overwrite pc->mem_cgroup.
> > - add page to LRU after overwrite pc->mem_cgroup.
> >
> > And we need to taking care of pagevec.
> >
> > If PageLRU(page) is set before we add PCG_USED bit, the page
> > will not be added to memcg's LRU (in short period).
> > So, regardlress of PageLRU(page) value before commit_charge(),
> > we need to check PageLRU(page) after commit_charge().
> >
> > Changelog:
> > - clean up.
> > - cover !PageLRU() by pagevec case.
> >
> >
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > ---
> > mm/memcontrol.c | 53 ++++++++++++++++++++++++++++++++++-------------------
> > 1 file changed, 34 insertions(+), 19 deletions(-)
> >
> > Index: mmotm-0303/mm/memcontrol.c
> > ===================================================================
> > --- mmotm-0303.orig/mm/memcontrol.c
> > +++ mmotm-0303/mm/memcontrol.c
> > @@ -926,13 +926,12 @@ void mem_cgroup_add_lru_list(struct page
> > }
> >
> > /*
> > - * At handling SwapCache, pc->mem_cgroup may be changed while it's linked to
> > - * lru because the page may.be reused after it's fully uncharged (because of
> > - * SwapCache behavior).To handle that, unlink page_cgroup from LRU when charge
> > - * it again. This function is only used to charge SwapCache. It's done under
> > - * lock_page and expected that zone->lru_lock is never held.
> > + * At handling SwapCache and other FUSE stuff, pc->mem_cgroup may be changed
> > + * while it's linked to lru because the page may be reused after it's fully
> > + * uncharged. To handle that, unlink page_cgroup from LRU when charge it again.
> > + * It's done under lock_page and expected that zone->lru_lock isnever held.
> > */
> > -static void mem_cgroup_lru_del_before_commit_swapcache(struct page *page)
> > +static void mem_cgroup_lru_del_before_commit(struct page *page)
> > {
> > unsigned long flags;
> > struct zone *zone = page_zone(page);
> > @@ -948,7 +947,7 @@ static void mem_cgroup_lru_del_before_co
> > spin_unlock_irqrestore(&zone->lru_lock, flags);
> > }
> >
> > -static void mem_cgroup_lru_add_after_commit_swapcache(struct page *page)
> > +static void mem_cgroup_lru_add_after_commit(struct page *page)
> > {
> > unsigned long flags;
> > struct zone *zone = page_zone(page);
> > @@ -2431,9 +2430,28 @@ static void
> > __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
> > enum charge_type ctype);
> >
> > +static void
> > +__mem_cgroup_commit_charge_lrucare(struct page *page, struct mem_cgroup *mem,
> > + enum charge_type ctype)
> > +{
> > + struct page_cgroup *pc = lookup_page_cgroup(page);
> > + /*
> > + * In some case, SwapCache, FUSE(splice_buf->radixtree), the page
> > + * is already on LRU. It means the page may on some other page_cgroup's
> > + * LRU. Take care of it.
> > + */
> > + if (unlikely(PageLRU(page)))
> > + mem_cgroup_lru_del_before_commit(page);
> > + __mem_cgroup_commit_charge(mem, page, 1, pc, ctype);
> > + if (unlikely(PageLRU(page)))
> > + mem_cgroup_lru_add_after_commit(page);
> > + return;
> > +}
> > +
> > int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
> > gfp_t gfp_mask)
> > {
> > + struct mem_cgroup *mem = NULL;
> > int ret;
> >
> > if (mem_cgroup_disabled())
> > @@ -2468,14 +2486,15 @@ int mem_cgroup_cache_charge(struct page
> > if (unlikely(!mm))
> > mm = &init_mm;
> >
> > - if (page_is_file_cache(page))
> > - return mem_cgroup_charge_common(page, mm, gfp_mask,
> > - MEM_CGROUP_CHARGE_TYPE_CACHE);
> > -
> > + if (page_is_file_cache(page)) {
> > + ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, &mem, true);
> > + if (ret || !mem)
> > + return ret;
> > + __mem_cgroup_commit_charge_lrucare(page, mem,
> > + MEM_CGROUP_CHARGE_TYPE_CACHE);
> > + }
> We should do "return 0" here, or do:
>
> } else {
> /* shmem */
> if (PageSwapCache(page)) {
> ..
> } else {
> ..
> }
> }
>
> Otherwise, the page cache will be charged twice.
>
Ahh, thanks. I'll send v3.
-Kame
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