Re: [PATCH v2] memcg: add vmscan_stat

[Andrew Bresticker <abrestic@google.com>]

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

From: Andrew Bresticker <abrestic@google.com>
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 <abrestic@google.com>
---
 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 <abrestic@google.com> wrote:
>
> > On Mon, Jul 11, 2011 at 3:30 AM, KAMEZAWA Hiroyuki <
> > kamezawa.hiroyu@jp.fujitsu.com> wrote:
> >
> > >
> > > 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..."
> > > 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:
> > >  - 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.
> > > +
> > > +elapsed_ns is a elapsed time in nanosecond. This may include sleep
> time
> > > +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
> > > 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)
> */
> > > +       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
> */
> > > +};
> > > +
> > >  #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,
> > > +                                                 gfp_t gfp_mask, bool
> > > noswap,
> > > +                                                 struct
> memcg_scanrecord
> > > *rec);
> > > +extern unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup
> *mem,
> > > +                                               gfp_t gfp_mask, bool
> > > noswap,
> > > +                                               struct zone *zone,
> > > +                                               struct memcg_scanrecord
> > > *rec,
> > > +                                               unsigned long
> *nr_scanned);
> > > +
> > >  #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);
> > > -extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup
> *mem,
> > > -                                                 gfp_t gfp_mask, bool
> > > noswap);
> > > -extern unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup
> *mem,
> > > -                                               gfp_t gfp_mask, bool
> > > noswap,
> > > -                                               struct zone *zone,
> > > -                                               unsigned long
> *nr_scanned);
> > >  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
> > 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.
>
>
> > I've also modified your patch to use per-cpu counters instead of
> spin-lock
> > 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;
> > 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
> > any insight as to why this is.  I can provide my diff against your patch
> if
> > 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
>
>
>

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