Re: [patch 1/3] mm: embed the memcg pointer directly into struct page

[Johannes Weiner <hannes@cmpxchg.org>]

On Tue, Nov 04, 2014 at 05:36:39PM +0900, Kamezawa Hiroyuki wrote:
> (2014/11/02 12:15), Johannes Weiner wrote:
> > 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 <kamezawa.hiroyu@jp.fujitsu.com>

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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