I've extended your patch to track write-back during page reclaim:
---

From: Andrew Bresticker <redacted>
Date: Thu, 14 Jul 2011 17:56:48 -0700
Subject: [PATCH] vmscan: Track number of pages written back during page
reclaim.

This tracks pages written out during page reclaim in memory.vmscan_stat
and breaks it down by file vs. anon and context (like "scanned_pages",
"rotated_pages", etc.).

Example output:
$ mkdir /dev/cgroup/memory/1
$ echo 8m > /dev/cgroup/memory/1/memory.limit_in_bytes
$ echo $$ > /dev/cgroup/memory/1/tasks
$ dd if=/dev/urandom of=file_20g bs=4096 count=524288
$ cat /dev/cgroup/memory/1/memory.vmscan_stat
...
written_pages_by_limit 36
written_anon_pages_by_limit 0
written_file_pages_by_limit 36
...
written_pages_by_limit_under_hierarchy 28
written_anon_pages_by_limit_under_hierarchy 0
written_file_pages_by_limit_under_hierarchy 28

Signed-off-by: Andrew Bresticker <redacted>
---
 include/linux/memcontrol.h |    1 +
 mm/memcontrol.c            |   12 ++++++++++++
 mm/vmscan.c                |   10 +++++++---
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 4b49edf..4be907e 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h

@@ -46,6 +46,7 @@ struct memcg_scanrecord {
  unsigned long nr_scanned[2]; /* the number of scanned pages */
  unsigned long nr_rotated[2]; /* the number of rotated pages */
  unsigned long nr_freed[2]; /* the number of freed pages */
+ unsigned long nr_written[2]; /* the number of pages written back */
  unsigned long elapsed; /* nsec of time elapsed while scanning */
 };

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9bb6e93..5ec2aa3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -221,6 +221,9 @@ enum {
  FREED,
  FREED_ANON,
  FREED_FILE,
+ WRITTEN,
+ WRITTEN_ANON,
+ WRITTEN_FILE,
  ELAPSED,
  NR_SCANSTATS,
 };

@@ -241,6 +244,9 @@ const char *scanstat_string[NR_SCANSTATS] = {
  "freed_pages",
  "freed_anon_pages",
  "freed_file_pages",
+ "written_pages",
+ "written_anon_pages",
+ "written_file_pages",
  "elapsed_ns",
 };
 #define SCANSTAT_WORD_LIMIT    "_by_limit"

@@ -1682,6 +1688,10 @@ static void __mem_cgroup_record_scanstat(unsigned

long *stats,
         stats[FREED_ANON] += rec->nr_freed[0];
         stats[FREED_FILE] += rec->nr_freed[1];

+ stats[WRITTEN] += rec->nr_written[0] + rec->nr_written[1];
+ stats[WRITTEN_ANON] += rec->nr_written[0];
+ stats[WRITTEN_FILE] += rec->nr_written[1];
+
         stats[ELAPSED] += rec->elapsed;
 }

@@ -1794,6 +1804,8 @@ static int mem_cgroup_hierarchical_reclaim(struct

mem_cgroup *root_mem,
                 rec.nr_rotated[1] = 0;
                 rec.nr_freed[0] = 0;
                 rec.nr_freed[1] = 0;
+ rec.nr_written[0] = 0;
+ rec.nr_written[1] = 0;
                 rec.elapsed = 0;
  /* we use swappiness of local cgroup */
  if (check_soft) {

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 8fb1abd..f73b96e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c

@@ -719,7 +719,7 @@ static noinline_for_stack void free_page_list(struct

list_head *free_pages)
  */
 static unsigned long shrink_page_list(struct list_head *page_list,
       struct zone *zone,
-      struct scan_control *sc)
+      struct scan_control *sc, int file)
 {
  LIST_HEAD(ret_pages);
  LIST_HEAD(free_pages);

@@ -727,6 +727,7 @@ static unsigned long shrink_page_list(struct list_head

*page_list,
  unsigned long nr_dirty = 0;
  unsigned long nr_congested = 0;
  unsigned long nr_reclaimed = 0;
+ unsigned long nr_written = 0;

  cond_resched();

@@ -840,6 +841,7 @@ static unsigned long shrink_page_list(struct list_head

*page_list,
  case PAGE_ACTIVATE:
  goto activate_locked;
  case PAGE_SUCCESS:
+ nr_written++;
  if (PageWriteback(page))
  goto keep_lumpy;
  if (PageDirty(page))

@@ -958,6 +960,8 @@ keep_lumpy:
  free_page_list(&free_pages);

  list_splice(&ret_pages, page_list);
+ if (!scanning_global_lru(sc))
+ sc->memcg_record->nr_written[file] += nr_written;
  count_vm_events(PGACTIVATE, pgactivate);
  return nr_reclaimed;
 }

@@ -1463,7 +1467,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct

zone *zone,

  spin_unlock_irq(&zone->lru_lock);

- nr_reclaimed = shrink_page_list(&page_list, zone, sc);
+ nr_reclaimed = shrink_page_list(&page_list, zone, sc, file);

  if (!scanning_global_lru(sc))
  sc->memcg_record->nr_freed[file] += nr_reclaimed;

@@ -1471,7 +1475,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct

zone *zone,
  /* Check if we should syncronously wait for writeback */
  if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) {
  set_reclaim_mode(priority, sc, true);
- nr_reclaimed += shrink_page_list(&page_list, zone, sc);
+ nr_reclaimed += shrink_page_list(&page_list, zone, sc, file);
  }

  local_irq_disable();
-- 
1.7.3.1

Thanks,
Andrew

On Wed, Jul 13, 2011 at 5:02 PM, KAMEZAWA Hiroyuki <
kamezawa.hiroyu@jp.fujitsu.com> wrote:

On Tue, 12 Jul 2011 16:02:02 -0700
Andrew Bresticker [off-list ref] wrote:

quoted

On Mon, Jul 11, 2011 at 3:30 AM, KAMEZAWA Hiroyuki <
kamezawa.hiroyu@jp.fujitsu.com> wrote:

quoted

This patch is onto mmotm-0710... got bigger than expected ;(
==
[PATCH] add memory.vmscan_stat

commit log of commit 0ae5e89 " memcg: count the soft_limit reclaim

in..."

quoted

quoted

says it adds scanning stats to memory.stat file. But it doesn't because
we considered we needed to make a concensus for such new APIs.

This patch is a trial to add memory.scan_stat. This shows
 - the number of scanned pages(total, anon, file)
 - the number of rotated pages(total, anon, file)
 - the number of freed pages(total, anon, file)
 - the number of elaplsed time (including sleep/pause time)

 for both of direct/soft reclaim.

The biggest difference with oringinal Ying's one is that this file
can be reset by some write, as

 # echo 0 ...../memory.scan_stat

Example of output is here. This is a result after make -j 6 kernel
under 300M limit.

[kamezawa@bluextal ~]$ cat /cgroup/memory/A/memory.scan_stat
[kamezawa@bluextal ~]$ cat /cgroup/memory/A/memory.vmscan_stat
scanned_pages_by_limit 9471864
scanned_anon_pages_by_limit 6640629
scanned_file_pages_by_limit 2831235
rotated_pages_by_limit 4243974
rotated_anon_pages_by_limit 3971968
rotated_file_pages_by_limit 272006
freed_pages_by_limit 2318492
freed_anon_pages_by_limit 962052
freed_file_pages_by_limit 1356440
elapsed_ns_by_limit 351386416101
scanned_pages_by_system 0
scanned_anon_pages_by_system 0
scanned_file_pages_by_system 0
rotated_pages_by_system 0
rotated_anon_pages_by_system 0
rotated_file_pages_by_system 0
freed_pages_by_system 0
freed_anon_pages_by_system 0
freed_file_pages_by_system 0
elapsed_ns_by_system 0
scanned_pages_by_limit_under_hierarchy 9471864
scanned_anon_pages_by_limit_under_hierarchy 6640629
scanned_file_pages_by_limit_under_hierarchy 2831235
rotated_pages_by_limit_under_hierarchy 4243974
rotated_anon_pages_by_limit_under_hierarchy 3971968
rotated_file_pages_by_limit_under_hierarchy 272006
freed_pages_by_limit_under_hierarchy 2318492
freed_anon_pages_by_limit_under_hierarchy 962052
freed_file_pages_by_limit_under_hierarchy 1356440
elapsed_ns_by_limit_under_hierarchy 351386416101
scanned_pages_by_system_under_hierarchy 0
scanned_anon_pages_by_system_under_hierarchy 0
scanned_file_pages_by_system_under_hierarchy 0
rotated_pages_by_system_under_hierarchy 0
rotated_anon_pages_by_system_under_hierarchy 0
rotated_file_pages_by_system_under_hierarchy 0
freed_pages_by_system_under_hierarchy 0
freed_anon_pages_by_system_under_hierarchy 0
freed_file_pages_by_system_under_hierarchy 0
elapsed_ns_by_system_under_hierarchy 0


total_xxxx is for hierarchy management.

This will be useful for further memcg developments and need to be
developped before we do some complicated rework on LRU/softlimit
management.

This patch adds a new struct memcg_scanrecord into scan_control struct.
sc->nr_scanned at el is not designed for exporting information. For
example,
nr_scanned is reset frequentrly and incremented +2 at scanning mapped
pages.

For avoiding complexity, I added a new param in scan_control which is

for

quoted

quoted

exporting scanning score.

Signed-off-by: KAMEZAWA Hiroyuki <redacted>

Changelog:
 - renamed as vmscan_stat
 - handle file/anon
 - added "rotated"
 - changed names of param in vmscan_stat.
---
 Documentation/cgroups/memory.txt |   85 +++++++++++++++++++
 include/linux/memcontrol.h       |   19 ++++
 include/linux/swap.h             |    6 -
 mm/memcontrol.c                  |  172
+++++++++++++++++++++++++++++++++++++--
 mm/vmscan.c                      |   39 +++++++-
 5 files changed, 303 insertions(+), 18 deletions(-)

Index: mmotm-0710/Documentation/cgroups/memory.txt
===================================================================

--- mmotm-0710.orig/Documentation/cgroups/memory.txt
+++ mmotm-0710/Documentation/cgroups/memory.txt

@@ -380,7 +380,7 @@ will be charged as a new owner of it.

 5.2 stat file

-memory.stat file includes following statistics
+5.2.1 memory.stat file includes following statistics

 # per-memory cgroup local status
 cache          - # of bytes of page cache memory.

@@ -438,6 +438,89 @@ Note:
        file_mapped is accounted only when the memory cgroup is owner

of

quoted

quoted

page
        cache.)

+5.2.2 memory.vmscan_stat
+
+memory.vmscan_stat includes statistics information for memory scanning

and

quoted

quoted

+freeing, reclaiming. The statistics shows memory scanning information
since
+memory cgroup creation and can be reset to 0 by writing 0 as
+
+ #echo 0 > ../memory.vmscan_stat
+
+This file contains following statistics.
+
+[param]_[file_or_anon]_pages_by_[reason]_[under_heararchy]
+[param]_elapsed_ns_by_[reason]_[under_hierarchy]
+
+For example,
+
+  scanned_file_pages_by_limit indicates the number of scanned
+  file pages at vmscan.
+
+Now, 3 parameters are supported
+
+  scanned - the number of pages scanned by vmscan
+  rotated - the number of pages activated at vmscan
+  freed   - the number of pages freed by vmscan
+
+If "rotated" is high against scanned/freed, the memcg seems busy.
+
+Now, 2 reason are supported
+
+  limit - the memory cgroup's limit
+  system - global memory pressure + softlimit
+           (global memory pressure not under softlimit is not handled

now)

quoted

quoted

+
+When under_hierarchy is added in the tail, the number indicates the
+total memcg scan of its children and itself.
+
+elapsed_ns is a elapsed time in nanosecond. This may include sleep

time

quoted

quoted

+and not indicates CPU usage. So, please take this as just showing
+latency.
+
+Here is an example.
+
+# cat /cgroup/memory/A/memory.vmscan_stat
+scanned_pages_by_limit 9471864
+scanned_anon_pages_by_limit 6640629
+scanned_file_pages_by_limit 2831235
+rotated_pages_by_limit 4243974
+rotated_anon_pages_by_limit 3971968
+rotated_file_pages_by_limit 272006
+freed_pages_by_limit 2318492
+freed_anon_pages_by_limit 962052
+freed_file_pages_by_limit 1356440
+elapsed_ns_by_limit 351386416101
+scanned_pages_by_system 0
+scanned_anon_pages_by_system 0
+scanned_file_pages_by_system 0
+rotated_pages_by_system 0
+rotated_anon_pages_by_system 0
+rotated_file_pages_by_system 0
+freed_pages_by_system 0
+freed_anon_pages_by_system 0
+freed_file_pages_by_system 0
+elapsed_ns_by_system 0
+scanned_pages_by_limit_under_hierarchy 9471864
+scanned_anon_pages_by_limit_under_hierarchy 6640629
+scanned_file_pages_by_limit_under_hierarchy 2831235
+rotated_pages_by_limit_under_hierarchy 4243974
+rotated_anon_pages_by_limit_under_hierarchy 3971968
+rotated_file_pages_by_limit_under_hierarchy 272006
+freed_pages_by_limit_under_hierarchy 2318492
+freed_anon_pages_by_limit_under_hierarchy 962052
+freed_file_pages_by_limit_under_hierarchy 1356440
+elapsed_ns_by_limit_under_hierarchy 351386416101
+scanned_pages_by_system_under_hierarchy 0
+scanned_anon_pages_by_system_under_hierarchy 0
+scanned_file_pages_by_system_under_hierarchy 0
+rotated_pages_by_system_under_hierarchy 0
+rotated_anon_pages_by_system_under_hierarchy 0
+rotated_file_pages_by_system_under_hierarchy 0
+freed_pages_by_system_under_hierarchy 0
+freed_anon_pages_by_system_under_hierarchy 0
+freed_file_pages_by_system_under_hierarchy 0
+elapsed_ns_by_system_under_hierarchy 0
+
 5.3 swappiness

 Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of

groups

quoted

quoted

only.
Index: mmotm-0710/include/linux/memcontrol.h
===================================================================

--- mmotm-0710.orig/include/linux/memcontrol.h
+++ mmotm-0710/include/linux/memcontrol.h

@@ -39,6 +39,16 @@ extern unsigned long mem_cgroup_isolate_
                                       struct mem_cgroup *mem_cont,
                                       int active, int file);

+struct memcg_scanrecord {
+       struct mem_cgroup *mem; /* scanend memory cgroup */
+       struct mem_cgroup *root; /* scan target hierarchy root */
+       int context;            /* scanning context (see memcontrol.c)

*/

quoted

quoted

+       unsigned long nr_scanned[2]; /* the number of scanned pages */
+       unsigned long nr_rotated[2]; /* the number of rotated pages */
+       unsigned long nr_freed[2]; /* the number of freed pages */
+       unsigned long elapsed; /* nsec of time elapsed while scanning

*/

quoted

quoted

+};
+
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
 /*
 * All "charge" functions with gfp_mask should use GFP_KERNEL or

@@ -117,6 +127,15 @@ mem_cgroup_get_reclaim_stat_from_page(st
 extern void mem_cgroup_print_oom_info(struct mem_cgroup *memcg,
                                       struct task_struct *p);

+extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup

*mem,

quoted

quoted

+                                                 gfp_t gfp_mask, bool
noswap,
+                                                 struct

memcg_scanrecord

quoted

quoted

*rec);
+extern unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup

*mem,

quoted

quoted

+                                               gfp_t gfp_mask, bool
noswap,
+                                               struct zone *zone,
+                                               struct memcg_scanrecord
*rec,
+                                               unsigned long

*nr_scanned);

quoted

quoted

+
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
 extern int do_swap_account;
 #endif
Index: mmotm-0710/include/linux/swap.h
===================================================================

--- mmotm-0710.orig/include/linux/swap.h
+++ mmotm-0710/include/linux/swap.h

@@ -253,12 +253,6 @@ static inline void lru_cache_add_file(st
 /* linux/mm/vmscan.c */
 extern unsigned long try_to_free_pages(struct zonelist *zonelist, int

order,
                                       gfp_t gfp_mask, nodemask_t

*mask);

quoted

quoted

-extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup

*mem,

quoted

quoted

-                                                 gfp_t gfp_mask, bool
noswap);
-extern unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup

*mem,

quoted

quoted

-                                               gfp_t gfp_mask, bool
noswap,
-                                               struct zone *zone,
-                                               unsigned long

*nr_scanned);

quoted

quoted

 extern int __isolate_lru_page(struct page *page, int mode, int file);
 extern unsigned long shrink_all_memory(unsigned long nr_pages);
 extern int vm_swappiness;
Index: mmotm-0710/mm/memcontrol.c
===================================================================

--- mmotm-0710.orig/mm/memcontrol.c
+++ mmotm-0710/mm/memcontrol.c

@@ -204,6 +204,50 @@ struct mem_cgroup_eventfd_list {
 static void mem_cgroup_threshold(struct mem_cgroup *mem);
 static void mem_cgroup_oom_notify(struct mem_cgroup *mem);

+enum {
+       SCAN_BY_LIMIT,
+       SCAN_BY_SYSTEM,
+       NR_SCAN_CONTEXT,
+       SCAN_BY_SHRINK, /* not recorded now */
+};
+
+enum {
+       SCAN,
+       SCAN_ANON,
+       SCAN_FILE,
+       ROTATE,
+       ROTATE_ANON,
+       ROTATE_FILE,
+       FREED,
+       FREED_ANON,
+       FREED_FILE,
+       ELAPSED,
+       NR_SCANSTATS,
+};
+
+struct scanstat {
+       spinlock_t      lock;
+       unsigned long   stats[NR_SCAN_CONTEXT][NR_SCANSTATS];
+       unsigned long   rootstats[NR_SCAN_CONTEXT][NR_SCANSTATS];
+};

I'm working on a similar effort with Ying here at Google and so far we've
been using per-cpu counters for these statistics instead of spin-lock
protected counters.  Clearly the spin-lock protected counters have less
memory overhead and make reading the stat file faster, but our concern is
that this method is inconsistent with the other memory stat files such
/proc/vmstat and /dev/cgroup/memory/.../memory.stat.  Is there any
particular reason you chose to use spin-lock protected counters instead

of

quoted

per-cpu counters?

In my experience, if we do "batch" enouch, it works always better than
percpu-counter. percpu counter is effective when batching is difficult.
This patch's implementation does enough batching and it's much coarse
grained than percpu counter. Then, this patch is better than percpu.

quoted

I've also modified your patch to use per-cpu counters instead of

spin-lock

quoted

protected counters.  I tested it by doing streaming I/O from a ramdisk:

$ mke2fs /dev/ram1
$ mkdir /tmp/swapram
$ mkdir /tmp/swapram/ram1
$ mount -t ext2 /dev/ram1 /tmp/swapram/ram1
$ dd if=/dev/urandom of=/tmp/swapram/ram1/file_16m bs=4096 count=4096
$ mkdir /dev/cgroup/memory/1
$ echo 8m > /dev/cgroup/memory/1
$ ./ramdisk_load.sh 7
$ echo $$ > /dev/cgroup/memory/1/tasks
$ time for ((z=0; z<=2000; z++)); do cat /tmp/swapram/ram1/file_16m >
/dev/zero; done

Where ramdisk_load.sh is:
for ((i=0; i<=$1; i++))
do
  echo $$ >/dev/cgroup/memory/1/tasks
  for ((z=0; z<=2000; z++)); do cat /tmp/swapram/ram1/file_16m >

/dev/zero;

quoted

done &
done

Surprisingly, the per-cpu counters perform worse than the spin-lock
protected counters.  Over 10 runs of the test above, the per-cpu counters
were 1.60% slower in both real time and sys time.  I'm wondering if you

have

quoted

any insight as to why this is.  I can provide my diff against your patch

if

quoted

necessary.

The percpu counte works effectively only when we use +1/-1 at each change
of
counters. It uses "batch" to merge the per-cpu value to the counter.
I think you use default "batch" value but the scan/rotate/free/elapsed
value
is always larger than "batch" and you just added memory overhead and "if"
to pure spinlock counters.

Determining this "batch" threshold for percpu counter is difficult.

Thanks,
-Kame