[RFC][PATCH 2/6] memcg: account swapcache

KAMEZAWA Hiroyuki
2008-11-12T03:28:13Z

SwapCache support for memory resource controller (memcg)

Before mem+swap controller, memcg itself should handle SwapCache in proper way.
This is cut-out from it.

In current memcg, SwapCache is just leaked and the user can create tons of
SwapCache. This is a 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 migration, check against 'old page' is modified to handle shmem.

Comparing to the old version discussed (and caused troubles), we have
advantages of
- PCG_USED bit.
- simple migrating handling.

So, situation is much easier than several months ago, maybe.

Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Tested-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

---
Documentation/controllers/memory.txt | 5 ++
include/linux/swap.h | 16 ++++++++
mm/memcontrol.c | 67 +++++++++++++++++++++++++++++++----
mm/shmem.c | 18 ++++++++-
mm/swap_state.c | 1
5 files changed, 99 insertions(+), 8 deletions(-)

Index: mmotm-2.6.28-Nov10/mm/memcontrol.c
===================================================================
--- mmotm-2.6.28-Nov10.orig/mm/memcontrol.c
+++ mmotm-2.6.28-Nov10/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>
@@ -146,6 +147,7 @@ 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,
};

@@ -803,6 +805,33 @@ 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, bool locked)
+{
+ int ret = 0;
+
+ if (mem_cgroup_subsys.disabled)
+ return 0;
+ if (unlikely(!mm))
+ mm = &init_mm;
+ if (!locked)
+ lock_page(page);
+ /*
+ * If not locked, the page can be dropped from SwapCache until
+ * we reach here.
+ */
+ if (PageSwapCache(page)) {
+ ret = mem_cgroup_charge_common(page, mm, mask,
+ MEM_CGROUP_CHARGE_TYPE_SHMEM, NULL);
+ }
+ if (!locked)
+ unlock_page(page);
+
+ return ret;
+}
+#endif
+
void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
{
struct page_cgroup *pc;
@@ -840,6 +869,9 @@ __mem_cgroup_uncharge_common(struct page
if (mem_cgroup_subsys.disabled)
return;

+ if (PageSwapCache(page))
+ return;
+
/*
* Check if our page_cgroup is valid
*/
@@ -848,12 +880,26 @@ __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;

@@ -867,6 +913,10 @@ __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)
@@ -886,6 +936,11 @@ 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.
@@ -943,7 +998,7 @@ 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-Nov10/mm/swap_state.c
===================================================================
--- mmotm-2.6.28-Nov10.orig/mm/swap_state.c
+++ mmotm-2.6.28-Nov10/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-Nov10/include/linux/swap.h
===================================================================
--- mmotm-2.6.28-Nov10.orig/include/linux/swap.h
+++ mmotm-2.6.28-Nov10/include/linux/swap.h
@@ -335,6 +335,22 @@ 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, bool locked);
+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, bool locked)
+{
+ 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-Nov10/mm/shmem.c
===================================================================
--- mmotm-2.6.28-Nov10.orig/mm/shmem.c
+++ mmotm-2.6.28-Nov10/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, true);
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, false)) {
+ page_cache_release(swappage);
+ error = -ENOMEM;
+ goto failed;
+ }
page_cache_release(swappage);
goto repeat;
}
Index: mmotm-2.6.28-Nov10/Documentation/controllers/memory.txt
===================================================================
--- mmotm-2.6.28-Nov10.orig/Documentation/controllers/memory.txt
+++ mmotm-2.6.28-Nov10/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