On Tue, Nov 04, 2014 at 05:36:39PM +0900, Kamezawa Hiroyuki wrote:

(2014/11/02 12:15), Johannes Weiner wrote:

quoted

Memory cgroups used to have 5 per-page pointers.  To allow users to
disable that amount of overhead during runtime, those pointers were
allocated in a separate array, with a translation layer between them
and struct page.

There is now only one page pointer remaining: the memcg pointer, that
indicates which cgroup the page is associated with when charged.  The
complexity of runtime allocation and the runtime translation overhead
is no longer justified to save that *potential* 0.19% of memory.  With
CONFIG_SLUB, page->mem_cgroup actually sits in the doubleword padding
after the page->private member and doesn't even increase struct page,
and then this patch actually saves space.  Remaining users that care
can still compile their kernels without CONFIG_MEMCG.

    text    data     bss     dec     hex     filename
8828345 1725264  983040 11536649 b00909  vmlinux.old
8827425 1725264  966656 11519345 afc571  vmlinux.new

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
  include/linux/memcontrol.h  |   6 +-
  include/linux/mm_types.h    |   5 +
  include/linux/mmzone.h      |  12 --
  include/linux/page_cgroup.h |  53 --------
  init/main.c                 |   7 -
  mm/memcontrol.c             | 124 +++++------------
  mm/page_alloc.c             |   2 -
  mm/page_cgroup.c            | 319 --------------------------------------------
  8 files changed, 41 insertions(+), 487 deletions(-)

Great! 
Acked-by: KAMEZAWA Hiroyuki <redacted>

Thank you!

BTW, init/Kconfig comments shouldn't be updated ?
(I'm sorry if it has been updated since your latest fix.)

Good point.  How about this?

---
From: Johannes Weiner <hannes@cmpxchg.org>
Subject: [patch] mm: move page->mem_cgroup bad page handling into generic code fix

Remove obsolete memory saving recommendations from the MEMCG Kconfig
help text.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 init/Kconfig | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 01b7f2a6abf7..d68d8b0780b3 100644
--- a/init/Kconfig
+++ b/init/Kconfig

@@ -983,18 +983,6 @@ config MEMCG
 	  Provides a memory resource controller that manages both anonymous
 	  memory and page cache. (See Documentation/cgroups/memory.txt)
 
-	  Note that setting this option increases fixed memory overhead
-	  associated with each page of memory in the system. By this,
-	  8(16)bytes/PAGE_SIZE on 32(64)bit system will be occupied by memory
-	  usage tracking struct at boot. Total amount of this is printed out
-	  at boot.
-
-	  Only enable when you're ok with these trade offs and really
-	  sure you need the memory resource controller. Even when you enable
-	  this, you can set "cgroup_disable=memory" at your boot option to
-	  disable memory resource controller and you can avoid overheads.
-	  (and lose benefits of memory resource controller)
-
 config MEMCG_SWAP
 	bool "Memory Resource Controller Swap Extension"
 	depends on MEMCG && SWAP

-- 
2.1.3

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