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    SubjectRe: [PATCH v3] memcg: add memory.vmscan_stat
    On Mon, 8 Aug 2011 14:43:33 +0200
    Johannes Weiner <jweiner@redhat.com> wrote:

    > On Fri, Jul 22, 2011 at 05:15:40PM +0900, KAMEZAWA Hiroyuki wrote:
    > > [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 <kamezawa.hiroyu@jp.fujitsu.com>
    > >
    > > 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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