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[dm-devel] Re: [PATCH 3/9] blkio-cgroup-v9: The new page_cgroup framework



On Wed, 22 Jul 2009 10:20:58 +0900
KAMEZAWA Hiroyuki <kamezawa hiroyu jp fujitsu com> wrote:

> On Tue, 21 Jul 2009 21:26:36 +0530
> Balbir Singh <balbir linux vnet ibm com> wrote:
> 
> > * Ryo Tsuruta <ryov valinux co jp> [2009-07-21 23:12:11]:
> > 
> > > This patch makes the page_cgroup framework be able to be used even if
> > > the compile option of the cgroup memory controller is off.
> > > So blkio-cgroup can use this framework without the memory controller.
> > > 
> > > Signed-off-by: Hirokazu Takahashi <taka valinux co jp>
> > > Signed-off-by: Ryo Tsuruta <ryov valinux co jp>
> > > 
> > > ---
> > >  include/linux/memcontrol.h  |    6 ++++++
> > >  include/linux/mmzone.h      |    4 ++--
> > >  include/linux/page_cgroup.h |    8 +++++---
> > >  init/Kconfig                |    4 ++++
> > >  mm/Makefile                 |    3 ++-
> > >  mm/memcontrol.c             |    6 ++++++
> > >  mm/page_cgroup.c            |    3 +--
> > >  7 files changed, 26 insertions(+), 8 deletions(-)
> > > 
> > > Index: linux-2.6.31-rc3/include/linux/memcontrol.h
> > > ===================================================================
> > > --- linux-2.6.31-rc3.orig/include/linux/memcontrol.h
> > > +++ linux-2.6.31-rc3/include/linux/memcontrol.h
> > > @@ -37,6 +37,8 @@ struct mm_struct;
> > >   * (Of course, if memcg does memory allocation in future, GFP_KERNEL is sane.)
> > >   */
> > > 
> > > +extern void __init_mem_page_cgroup(struct page_cgroup *pc);
> > > +
> > >  extern int mem_cgroup_newpage_charge(struct page *page, struct mm_struct *mm,
> > >  				gfp_t gfp_mask);
> > >  /* for swap handling */
> > > @@ -121,6 +123,10 @@ void mem_cgroup_update_mapped_file_stat(
> > >  #else /* CONFIG_CGROUP_MEM_RES_CTLR */
> > >  struct mem_cgroup;
> > > 
> > > +static inline void __init_mem_page_cgroup(struct page_cgroup *pc)
> > > +{
> > > +}
> > > +
> > >  static inline int mem_cgroup_newpage_charge(struct page *page,
> > >  					struct mm_struct *mm, gfp_t gfp_mask)
> > >  {
> > > Index: linux-2.6.31-rc3/include/linux/mmzone.h
> > > ===================================================================
> > > --- linux-2.6.31-rc3.orig/include/linux/mmzone.h
> > > +++ linux-2.6.31-rc3/include/linux/mmzone.h
> > > @@ -605,7 +605,7 @@ typedef struct pglist_data {
> > >  	int nr_zones;
> > >  #ifdef CONFIG_FLAT_NODE_MEM_MAP	/* means !SPARSEMEM */
> > >  	struct page *node_mem_map;
> > > -#ifdef CONFIG_CGROUP_MEM_RES_CTLR
> > > +#ifdef CONFIG_CGROUP_PAGE
> > >  	struct page_cgroup *node_page_cgroup;
> > >  #endif
> > >  #endif
> > > @@ -956,7 +956,7 @@ struct mem_section {
> > > 
> > >  	/* See declaration of similar field in struct zone */
> > >  	unsigned long *pageblock_flags;
> > > -#ifdef CONFIG_CGROUP_MEM_RES_CTLR
> > > +#ifdef CONFIG_CGROUP_PAGE
> > >  	/*
> > >  	 * If !SPARSEMEM, pgdat doesn't have page_cgroup pointer. We use
> > >  	 * section. (see memcontrol.h/page_cgroup.h about this.)
> > > Index: linux-2.6.31-rc3/include/linux/page_cgroup.h
> > > ===================================================================
> > > --- linux-2.6.31-rc3.orig/include/linux/page_cgroup.h
> > > +++ linux-2.6.31-rc3/include/linux/page_cgroup.h
> > > @@ -1,7 +1,7 @@
> > >  #ifndef __LINUX_PAGE_CGROUP_H
> > >  #define __LINUX_PAGE_CGROUP_H
> > > 
> > > -#ifdef CONFIG_CGROUP_MEM_RES_CTLR
> > > +#ifdef CONFIG_CGROUP_PAGE
> > >  #include <linux/bit_spinlock.h>
> > >  /*
> > >   * Page Cgroup can be considered as an extended mem_map.
> > > @@ -12,9 +12,11 @@
> > >   */
> > >  struct page_cgroup {
> > >  	unsigned long flags;
> > > -	struct mem_cgroup *mem_cgroup;
> > >  	struct page *page;
> > > +#ifdef CONFIG_CGROUP_MEM_RES_CTLR
> > > +	struct mem_cgroup *mem_cgroup;
> > >  	struct list_head lru;		/* per cgroup LRU list */
> > > +#endif
> > >  };
> > 
> > If CONFIG_CGROUP_MEM_RES_CTLR is not enabled and CGROUP_PAGE is
> > (assuming that the depends on below is refactored), what would this
> > change buy us? What is page_cgroup helping us track, the mem_cgroup is
> > factored out, so we are interested in the flags only?
> > 
> plz remove CONFIG. This jsut makes code complicated.
> or plz use your own infrastructure, not depends on page_cgroup.
> 

BTW, you can't modify page_cgroup->flags bit without cmpxchg.
Then, patch [5/9] is completely broken, now because new bit is used
with atomic bit ops but without lock_page_cgroup(). (see mmotm)

Why struct page's flags bit can includes zone id etc...is just because
it's initalized before using. Anyway, this is "flags" bit. If you want
to modify multiple bit at once, plz use cmpxchg.
Then, I buy patch [8/9] and just skip this patch.

But, following is more straightforward. (and what you do is not different
from this.)
==
struct page {
	.....
#ifdef CONFIG_BLOCKIO_CGROUP
	void *blockio_cgroup;
#endif
}
==


Regards,
-Kame




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