Re: [RFC][PATCH 3/14] memcg: atomic_flags

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Tue, 26 Aug 2008 10:25:55 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> > Before trying to modify memory resource controller, this atomic operation
> > on flags is necessary.
> > Changelog (v1) -> (v2)
> >  - no changes
> > Changelog  (preview) -> (v1):
> >  - patch ordering is changed.
> >  - Added macro for defining functions for Test/Set/Clear bit.
> >  - made the names of flags shorter.
> > 
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> > 
> > ---
> >  mm/memcontrol.c |  108 +++++++++++++++++++++++++++++++++++++++-----------------
> >  1 file changed, 77 insertions(+), 31 deletions(-)
> > 
> > Index: mmtom-2.6.27-rc3+/mm/memcontrol.c
> > ===================================================================
> > --- mmtom-2.6.27-rc3+.orig/mm/memcontrol.c
> > +++ mmtom-2.6.27-rc3+/mm/memcontrol.c
> > @@ -163,12 +163,57 @@ struct page_cgroup {
> >  	struct list_head lru;		/* per cgroup LRU list */
> >  	struct page *page;
> >  	struct mem_cgroup *mem_cgroup;
> > -	int flags;
> > +	unsigned long flags;
> >  };
> > -#define PAGE_CGROUP_FLAG_CACHE	   (0x1)	/* charged as cache */
> > -#define PAGE_CGROUP_FLAG_ACTIVE    (0x2)	/* page is active in this cgroup */
> > -#define PAGE_CGROUP_FLAG_FILE	   (0x4)	/* page is file system backed */
> > -#define PAGE_CGROUP_FLAG_UNEVICTABLE (0x8)	/* page is unevictableable */
> > +
> > +enum {
> > +	/* flags for mem_cgroup */
> > +	Pcg_CACHE, /* charged as cache */
> 
> Why Pcg_CACHE and not PCG_CACHE or PAGE_CGROUP_CACHE? I think the latter is more
> readable, no?
> 
Hmm, ok.


> > +	/* flags for LRU placement */
> > +	Pcg_ACTIVE, /* page is active in this cgroup */
> > +	Pcg_FILE, /* page is file system backed */
> > +	Pcg_UNEVICTABLE, /* page is unevictableable */
> > +};
> > +
> > +#define TESTPCGFLAG(uname, lname)			\
>                       ^^ uname and lname?
> How about TEST_PAGE_CGROUP_FLAG(func, bit)
> 
This style is from PageXXX macros and I like shorter name.


> > +static inline int Pcg##uname(struct page_cgroup *pc)	\
> > +	{ return test_bit(Pcg_##lname, &pc->flags); }
> > +
> 
> I would prefer PageCgroup##func
> 
Hmm..ok. I'll rewrite and see 80 columns problem.


> > +#define SETPCGFLAG(uname, lname)			\
> > +static inline void SetPcg##uname(struct page_cgroup *pc)\
> > +	{ set_bit(Pcg_##lname, &pc->flags);  }
> > +
> > +#define CLEARPCGFLAG(uname, lname)			\
> > +static inline void ClearPcg##uname(struct page_cgroup *pc)	\
> > +	{ clear_bit(Pcg_##lname, &pc->flags);  }
> > +
> > +#define __SETPCGFLAG(uname, lname)			\
> > +static inline void __SetPcg##uname(struct page_cgroup *pc)\
> > +	{ __set_bit(Pcg_##lname, &pc->flags);  }
> > +
> 
> OK, so we have the non-atomic verion as well
> 
> > +#define __CLEARPCGFLAG(uname, lname)			\
> > +static inline void __ClearPcg##uname(struct page_cgroup *pc)	\
> > +	{ __clear_bit(Pcg_##lname, &pc->flags);  }
> > +
> > +/* Cache flag is set only once (at allocation) */
> > +TESTPCGFLAG(Cache, CACHE)
> > +__SETPCGFLAG(Cache, CACHE)
> > +
> > +/* LRU management flags (from global-lru definition) */
> > +TESTPCGFLAG(File, FILE)
> > +SETPCGFLAG(File, FILE)
> > +__SETPCGFLAG(File, FILE)
> > +CLEARPCGFLAG(File, FILE)
> > +
> > +TESTPCGFLAG(Active, ACTIVE)
> > +SETPCGFLAG(Active, ACTIVE)
> > +__SETPCGFLAG(Active, ACTIVE)
> > +CLEARPCGFLAG(Active, ACTIVE)
> > +
> > +TESTPCGFLAG(Unevictable, UNEVICTABLE)
> > +SETPCGFLAG(Unevictable, UNEVICTABLE)
> > +CLEARPCGFLAG(Unevictable, UNEVICTABLE)
> > +
> > 
> >  static int page_cgroup_nid(struct page_cgroup *pc)
> >  {
> > @@ -189,14 +234,15 @@ enum charge_type {
> >  /*
> >   * Always modified under lru lock. Then, not necessary to preempt_disable()
> >   */
> > -static void mem_cgroup_charge_statistics(struct mem_cgroup *mem, int flags,
> > -					bool charge)
> > +static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
> > +					 struct page_cgroup *pc,
> > +					 bool charge)
> >  {
> >  	int val = (charge)? 1 : -1;
> >  	struct mem_cgroup_stat *stat = &mem->stat;
> > 
> >  	VM_BUG_ON(!irqs_disabled());
> > -	if (flags & PAGE_CGROUP_FLAG_CACHE)
> > +	if (PcgCache(pc))
> 
> Shouldn't we use __PcgCache(), see my comments below
> 
> >  		__mem_cgroup_stat_add_safe(stat, MEM_CGROUP_STAT_CACHE, val);
> >  	else
> >  		__mem_cgroup_stat_add_safe(stat, MEM_CGROUP_STAT_RSS, val);
> > @@ -289,18 +335,18 @@ static void __mem_cgroup_remove_list(str
> >  {
> >  	int lru = LRU_BASE;
> > 
> > -	if (pc->flags & PAGE_CGROUP_FLAG_UNEVICTABLE)
> > +	if (PcgUnevictable(pc))
> 
> Since we call this under a lock, can't we use __PcgUnevictable(pc)? If not, what
> are we buying by doing atomic operations under a lock?
> 
> >  		lru = LRU_UNEVICTABLE;
> >  	else {
> > -		if (pc->flags & PAGE_CGROUP_FLAG_ACTIVE)
> > +		if (PcgActive(pc))
> 
> Ditto
> 
> >  			lru += LRU_ACTIVE;
> > -		if (pc->flags & PAGE_CGROUP_FLAG_FILE)
> > +		if (PcgFile(pc))
> 
> Ditto
> 
> >  			lru += LRU_FILE;
> >  	}
> > 
> >  	MEM_CGROUP_ZSTAT(mz, lru) -= 1;
> > 
> > -	mem_cgroup_charge_statistics(pc->mem_cgroup, pc->flags, false);
> > +	mem_cgroup_charge_statistics(pc->mem_cgroup, pc, false);
> >  	list_del(&pc->lru);
> >  }
> > 
> > @@ -309,27 +355,27 @@ static void __mem_cgroup_add_list(struct
> >  {
> >  	int lru = LRU_BASE;
> > 
> > -	if (pc->flags & PAGE_CGROUP_FLAG_UNEVICTABLE)
> > +	if (PcgUnevictable(pc))
> 
> Ditto
> 
> >  		lru = LRU_UNEVICTABLE;
> >  	else {
> > -		if (pc->flags & PAGE_CGROUP_FLAG_ACTIVE)
> > +		if (PcgActive(pc))
> >  			lru += LRU_ACTIVE;
> > -		if (pc->flags & PAGE_CGROUP_FLAG_FILE)
> > +		if (PcgFile(pc))
> 
> Ditto
> 
> >  			lru += LRU_FILE;
> >  	}
> > 
> >  	MEM_CGROUP_ZSTAT(mz, lru) += 1;
> >  	list_add(&pc->lru, &mz->lists[lru]);
> > 
> > -	mem_cgroup_charge_statistics(pc->mem_cgroup, pc->flags, true);
> > +	mem_cgroup_charge_statistics(pc->mem_cgroup, pc, true);
> >  }
> > 
> >  static void __mem_cgroup_move_lists(struct page_cgroup *pc, enum lru_list lru)
> >  {
> >  	struct mem_cgroup_per_zone *mz = page_cgroup_zoneinfo(pc);
> > -	int active    = pc->flags & PAGE_CGROUP_FLAG_ACTIVE;
> > -	int file      = pc->flags & PAGE_CGROUP_FLAG_FILE;
> > -	int unevictable = pc->flags & PAGE_CGROUP_FLAG_UNEVICTABLE;
> > +	int active    = PcgActive(pc);
> > +	int file      = PcgFile(pc);
> > +	int unevictable = PcgUnevictable(pc);
> >  	enum lru_list from = unevictable ? LRU_UNEVICTABLE :
> >  				(LRU_FILE * !!file + !!active);
> > 
> > @@ -339,14 +385,14 @@ static void __mem_cgroup_move_lists(stru
> >  	MEM_CGROUP_ZSTAT(mz, from) -= 1;
> > 
> >  	if (is_unevictable_lru(lru)) {
> > -		pc->flags &= ~PAGE_CGROUP_FLAG_ACTIVE;
> > -		pc->flags |= PAGE_CGROUP_FLAG_UNEVICTABLE;
> > +		ClearPcgActive(pc);
> > +		SetPcgUnevictable(pc);
> >  	} else {
> >  		if (is_active_lru(lru))
> > -			pc->flags |= PAGE_CGROUP_FLAG_ACTIVE;
> > +			SetPcgActive(pc);
> >  		else
> > -			pc->flags &= ~PAGE_CGROUP_FLAG_ACTIVE;
> > -		pc->flags &= ~PAGE_CGROUP_FLAG_UNEVICTABLE;
> > +			ClearPcgActive(pc);
> > +		ClearPcgUnevictable(pc);
> 
> Again shouldn't we be using the __ variants?
> 

For testing, __ variants are ok, I think.
For setting/clearing, because we'll have PcgObsolete() flag or
some more flags later, atomic version is better.
(For example, PcgDirty() is in my plan.)

I'll check all again.

Thanks,
-Kame



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