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Date: Tue, 4 Nov 2008 17:42:01 +0900
From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
hugh@...itas.com, taka@...inux.co.jp, nishimura@....nes.nec.co.jp
Subject: Re: [RFC][PATCH 2/5] memcg : handle swap cache
On Fri, 31 Oct 2008 11:54:11 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> SwapCache support for memory resource controller (memcg)
>
> Before mem+swap controller, memcg itself should handle SwapCache in proper way.
>
> In current memcg, SwapCache is just leaked and the user can create tons of
> SwapCache. This is leak of account and should be handled.
>
> SwapCache accounting is done as following.
>
> charge (anon)
> - charged when it's mapped.
> (because of readahead, charge at add_to_swap_cache() is not sane)
> uncharge (anon)
> - uncharged when it's dropped from swapcache and fully unmapped.
> means it's not uncharged at unmap.
> Note: delete from swap cache at swap-in is done after rmap information
> is established.
> charge (shmem)
> - charged at swap-in. this prevents charge at add_to_page_cache().
>
> uncharge (shmem)
> - uncharged when it's dropped from swapcache and not on shmem's
> radix-tree.
>
> at migartion, check against 'old page' is modified to handle shmem.
>
> Compareing to the old version discussed (and caused troubles), we have
> advanteges of
> - PCG_USED bit.
> - simple migraton handling.
>
> So, situation is much easier than several months ago, maybe.
>
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
> ---
> Documentation/controllers/memory.txt | 5 ++
> include/linux/swap.h | 16 ++++++++
> mm/memcontrol.c | 66 +++++++++++++++++++++++++++++++----
> mm/shmem.c | 18 ++++++++-
> mm/swap_state.c | 1
> 5 files changed, 98 insertions(+), 8 deletions(-)
>
> Index: mmotm-2.6.28-rc2+/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.28-rc2+.orig/mm/memcontrol.c
> +++ mmotm-2.6.28-rc2+/mm/memcontrol.c
> @@ -21,6 +21,7 @@
> #include <linux/memcontrol.h>
> #include <linux/cgroup.h>
> #include <linux/mm.h>
> +#include <linux/pagemap.h>
> #include <linux/smp.h>
> #include <linux/page-flags.h>
> #include <linux/backing-dev.h>
> @@ -140,6 +141,7 @@ enum charge_type {
> MEM_CGROUP_CHARGE_TYPE_MAPPED,
> MEM_CGROUP_CHARGE_TYPE_SHMEM, /* used by page migration of shmem */
> MEM_CGROUP_CHARGE_TYPE_FORCE, /* used by force_empty */
> + MEM_CGROUP_CHARGE_TYPE_SWAPOUT, /* for accounting swapcache */
> NR_CHARGE_TYPE,
> };
>
> @@ -781,6 +783,32 @@ int mem_cgroup_cache_charge(struct page
> MEM_CGROUP_CHARGE_TYPE_SHMEM, NULL);
> }
>
> +#ifdef CONFIG_SWAP
> +int mem_cgroup_cache_charge_swapin(struct page *page,
> + struct mm_struct *mm, gfp_t mask)
> +{
> + int ret = 0;
> +
> + if (mem_cgroup_subsys.disabled)
> + return 0;
> + if (unlikely(!mm))
> + mm = &init_mm;
> +
> + ret = mem_cgroup_charge_common(page, mm, mask,
> + MEM_CGROUP_CHARGE_TYPE_SHMEM, NULL);
> + /*
> + * The page may be dropped from SwapCache because we don't have
> + * lock_page().This may cause charge-after-uncharge trouble.
> + * Fix it up here. (the caller have refcnt to this page and
> + * page itself is guaranteed not to be freed.)
> + */
> + if (ret && !PageSwapCache(page))
> + mem_cgroup_uncharge_swapcache(page);
> +
Hmm.. after [5/5], mem_cgroup_cache_charge_swapin has 'locked' parameter,
calls lock_page(if !locked), and checks PageSwapCache under page lock.
Why not doing it in this patch?
Thanks,
Daisuke Nishimura.
> + return ret;
> +}
> +#endif
> +
> void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
> {
> struct page_cgroup *pc;
> @@ -818,6 +846,9 @@ __mem_cgroup_uncharge_common(struct page
> if (mem_cgroup_subsys.disabled)
> return;
>
> + if (PageSwapCache(page))
> + return;
> +
> /*
> * Check if our page_cgroup is valid
> */
> @@ -826,12 +857,26 @@ __mem_cgroup_uncharge_common(struct page
> return;
>
> lock_page_cgroup(pc);
> - if ((ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED && page_mapped(page))
> - || !PageCgroupUsed(pc)) {
> - /* This happens at race in zap_pte_range() and do_swap_page()*/
> - unlock_page_cgroup(pc);
> - return;
> +
> + if (!PageCgroupUsed(pc))
> + goto unlock_out;
> +
> + switch(ctype) {
> + case MEM_CGROUP_CHARGE_TYPE_MAPPED:
> + if (page_mapped(page))
> + goto unlock_out;
> + break;
> + case MEM_CGROUP_CHARGE_TYPE_SWAPOUT:
> + if (!PageAnon(page)) { /* Shared memory */
> + if (page->mapping && !page_is_file_cache(page))
> + goto unlock_out;
> + } else if (page_mapped(page)) /* Anon */
> + goto unlock_out;
> + break;
> + default:
> + break;
> }
> +
> ClearPageCgroupUsed(pc);
> mem = pc->mem_cgroup;
>
> @@ -845,6 +890,10 @@ __mem_cgroup_uncharge_common(struct page
> css_put(&mem->css);
>
> return;
> +
> +unlock_out:
> + unlock_page_cgroup(pc);
> + return;
> }
>
> void mem_cgroup_uncharge_page(struct page *page)
> @@ -864,6 +913,11 @@ void mem_cgroup_uncharge_cache_page(stru
> __mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_CACHE);
> }
>
> +void mem_cgroup_uncharge_swapcache(struct page *page)
> +{
> + __mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_SWAPOUT);
> +}
> +
> /*
> * Before starting migration, account PAGE_SIZE to mem_cgroup that the old
> * page belongs to.
> @@ -921,7 +975,7 @@ void mem_cgroup_end_migration(struct mem
> ctype = MEM_CGROUP_CHARGE_TYPE_SHMEM;
>
> /* unused page is not on radix-tree now. */
> - if (unused && ctype != MEM_CGROUP_CHARGE_TYPE_MAPPED)
> + if (unused)
> __mem_cgroup_uncharge_common(unused, ctype);
>
> pc = lookup_page_cgroup(target);
> Index: mmotm-2.6.28-rc2+/mm/swap_state.c
> ===================================================================
> --- mmotm-2.6.28-rc2+.orig/mm/swap_state.c
> +++ mmotm-2.6.28-rc2+/mm/swap_state.c
> @@ -119,6 +119,7 @@ void __delete_from_swap_cache(struct pag
> total_swapcache_pages--;
> __dec_zone_page_state(page, NR_FILE_PAGES);
> INC_CACHE_INFO(del_total);
> + mem_cgroup_uncharge_swapcache(page);
> }
>
> /**
> Index: mmotm-2.6.28-rc2+/include/linux/swap.h
> ===================================================================
> --- mmotm-2.6.28-rc2+.orig/include/linux/swap.h
> +++ mmotm-2.6.28-rc2+/include/linux/swap.h
> @@ -332,6 +332,22 @@ static inline void disable_swap_token(vo
> put_swap_token(swap_token_mm);
> }
>
> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR
> +extern int mem_cgroup_cache_charge_swapin(struct page *page,
> + struct mm_struct *mm, gfp_t mask);
> +extern void mem_cgroup_uncharge_swapcache(struct page *page);
> +#else
> +static inline
> +int mem_cgroup_cache_charge_swapin(struct page *page,
> + struct mm_struct *mm, gfp_t mask)
> +{
> + return 0;
> +}
> +static inline void mem_cgroup_uncharge_swapcache(struct page *page)
> +{
> +}
> +#endif
> +
> #else /* CONFIG_SWAP */
>
> #define total_swap_pages 0
> Index: mmotm-2.6.28-rc2+/mm/shmem.c
> ===================================================================
> --- mmotm-2.6.28-rc2+.orig/mm/shmem.c
> +++ mmotm-2.6.28-rc2+/mm/shmem.c
> @@ -920,8 +920,12 @@ found:
> error = 1;
> if (!inode)
> goto out;
> - /* Charge page using GFP_HIGHUSER_MOVABLE while we can wait */
> - error = mem_cgroup_cache_charge(page, current->mm, GFP_HIGHUSER_MOVABLE);
> + /*
> + * Charge page using GFP_HIGHUSER_MOVABLE while we can wait.
> + * charged back to the user(not to caller) when swap account is used.
> + */
> + error = mem_cgroup_cache_charge_swapin(page,
> + current->mm, GFP_HIGHUSER_MOVABLE);
> if (error)
> goto out;
> error = radix_tree_preload(GFP_KERNEL);
> @@ -1258,6 +1262,16 @@ repeat:
> goto repeat;
> }
> wait_on_page_locked(swappage);
> + /*
> + * We want to avoid charge at add_to_page_cache().
> + * charge against this swap cache here.
> + */
> + if (mem_cgroup_cache_charge_swapin(swappage,
> + current->mm, gfp)) {
> + page_cache_release(swappage);
> + error = -ENOMEM;
> + goto failed;
> + }
> page_cache_release(swappage);
> goto repeat;
> }
> Index: mmotm-2.6.28-rc2+/Documentation/controllers/memory.txt
> ===================================================================
> --- mmotm-2.6.28-rc2+.orig/Documentation/controllers/memory.txt
> +++ mmotm-2.6.28-rc2+/Documentation/controllers/memory.txt
> @@ -137,6 +137,11 @@ behind this approach is that a cgroup th
> page will eventually get charged for it (once it is uncharged from
> the cgroup that brought it in -- this will happen on memory pressure).
>
> +Exception: When you do swapoff and make swapped-out pages of shmem(tmpfs) to
> +be backed into memory in force, charges for pages are accounted against the
> +caller of swapoff rather than the users of shmem.
> +
> +
> 2.4 Reclaim
>
> Each cgroup maintains a per cgroup LRU that consists of an active
>
--
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