On Mon, 8 Aug 2011 14:43:33 +0200
Johannes Weiner [off-list ref] wrote:

On Fri, Jul 22, 2011 at 05:15:40PM +0900, KAMEZAWA Hiroyuki wrote:

quoted

[PATCH] add memory.vmscan_stat

commit log of commit 0ae5e89 " memcg: count the soft_limit reclaim in..."
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
exporting scanning score.

Signed-off-by: KAMEZAWA Hiroyuki <redacted>

Changelog:
  - fixed the trigger for recording nr_freed in shrink_inactive_list()
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 page
 	 cache.)
 
+5.2.2 memory.vmscan_stat
+
+memory.vmscan_stat includes statistics information for memory scanning and
+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)
+
+When under_hierarchy is added in the tail, the number indicates the
+total memcg scan of its children and itself.

In your implementation, statistics are only accounted to the memcg
triggering the limit and the respectively scanned memcgs.

Consider the following setup:

	A
       / \
      B   C
     /
    D

If D tries to charge but hits the limit of A, then B's hierarchy
counters do not reflect the reclaim activity resulting in D.

yes, as I expected.

That's not consistent with how hierarchy counters usually operate, and
neither with how you documented it.

Hmm.

On a non-technical note: as Ying Han and I were the other two people
working on reclaim and statistics, it really irks me that neither of
us were CCd on this.  Especially on such a controversial change.

I always drop CC if no reply/review comes.

Thanks,
-Kame

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