Re: Low overhead patches for the memory cgroup controller (v4)

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

On Mon, 15 Jun 2009 00:07:40 +0530, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> Here is v4 of the patches, please review and comment
> 
> Feature: Remove the overhead associated with the root cgroup
> 
> From: Balbir Singh <balbir@linux.vnet.ibm.com>
> 
> changelog v4 -> v3
> 1. Rebase to mmotm 9th june 2009
> 2. Remove PageCgroupRoot, we have account LRU flags to indicate that
>    we do only accounting and no reclaim.
hmm, I prefer the previous version of PCG_ACCT_LRU meaning. It can be
used to remove annoying list_empty(&pc->lru) and !pc->mem_cgroup checks.

> 3. pcg_default_flags has been used again, since PCGF_ROOT is gone,
>    we set PCGF_ACCT_LRU only in mem_cgroup_add_lru_list
It might be safe, but I don't think it's a good idea to touch PCGF_ACCT_LRU
outside of zone->lru_lock.

IMHO, the most complicated case is a SwapCache which has been read ahead by
a *different* cpu from the cpu doing do_swap_page(). Those SwapCache can be
on page_vec and be drained to LRU asymmetrically with do_swap_page().
Well, yes it would be safe just because PCGF_ACCT_LRU would not be set
if PCGF_USED has not been set, but I don't think it's a good idea to touch
PCGF_ACCT_LRU outside of zone->lru_lock anyway.


Doesn't a patch like below work for you ?
Lightly tested under global memory pressure(w/o memcg's memory pressure)
on a small machine(just a bit modified from then though).

===
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
---
 include/linux/page_cgroup.h |   13 ++++++++++
 mm/memcontrol.c             |   54 +++++++++++++++++++++++++++++++-----------
 2 files changed, 53 insertions(+), 14 deletions(-)

diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
index 7339c7b..debd8ba 100644
--- a/include/linux/page_cgroup.h
+++ b/include/linux/page_cgroup.h
@@ -26,6 +26,7 @@ enum {
 	PCG_LOCK,  /* page cgroup is locked */
 	PCG_CACHE, /* charged as cache */
 	PCG_USED, /* this object is in use. */
+	PCG_ACCT_LRU, /* page has been accounted for */
 };
 
 #define TESTPCGFLAG(uname, lname)			\
@@ -40,11 +41,23 @@ static inline void SetPageCgroup##uname(struct page_cgroup *pc)\
 static inline void ClearPageCgroup##uname(struct page_cgroup *pc)	\
 	{ clear_bit(PCG_##lname, &pc->flags);  }
 
+#define TESTCLEARPCGFLAG(uname, lname)			\
+static inline int TestClearPageCgroup##uname(struct page_cgroup *pc)	\
+	{ return test_and_clear_bit(PCG_##lname, &pc->flags);  }
+
 /* Cache flag is set only once (at allocation) */
 TESTPCGFLAG(Cache, CACHE)
+CLEARPCGFLAG(Cache, CACHE)
+SETPCGFLAG(Cache, CACHE)
 
 TESTPCGFLAG(Used, USED)
 CLEARPCGFLAG(Used, USED)
+SETPCGFLAG(Used, USED)
+
+SETPCGFLAG(AcctLRU, ACCT_LRU)
+CLEARPCGFLAG(AcctLRU, ACCT_LRU)
+TESTPCGFLAG(AcctLRU, ACCT_LRU)
+TESTCLEARPCGFLAG(AcctLRU, ACCT_LRU)
 
 static inline int page_cgroup_nid(struct page_cgroup *pc)
 {
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index dbece65..820f3e6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -43,6 +43,7 @@
 
 struct cgroup_subsys mem_cgroup_subsys __read_mostly;
 #define MEM_CGROUP_RECLAIM_RETRIES	5
+struct mem_cgroup *root_mem_cgroup __read_mostly;
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
 /* Turned on only when memory cgroup is enabled && really_do_swap_account = 1 */
@@ -200,13 +201,8 @@ enum charge_type {
 #define PCGF_CACHE	(1UL << PCG_CACHE)
 #define PCGF_USED	(1UL << PCG_USED)
 #define PCGF_LOCK	(1UL << PCG_LOCK)
-static const unsigned long
-pcg_default_flags[NR_CHARGE_TYPE] = {
-	PCGF_CACHE | PCGF_USED | PCGF_LOCK, /* File Cache */
-	PCGF_USED | PCGF_LOCK, /* Anon */
-	PCGF_CACHE | PCGF_USED | PCGF_LOCK, /* Shmem */
-	0, /* FORCE */
-};
+/* Not used, but added here for completeness */
+#define PCGF_ACCT	(1UL << PCG_ACCT)
 
 /* for encoding cft->private value on file */
 #define _MEM			(0)
@@ -354,6 +350,11 @@ static int mem_cgroup_walk_tree(struct mem_cgroup *root, void *data,
 	return ret;
 }
 
+static inline bool mem_cgroup_is_root(struct mem_cgroup *mem)
+{
+	return (mem == root_mem_cgroup);
+}
+
 /*
  * Following LRU functions are allowed to be used without PCG_LOCK.
  * Operations are called by routine of global LRU independently from memcg.
@@ -371,22 +372,24 @@ static int mem_cgroup_walk_tree(struct mem_cgroup *root, void *data,
 void mem_cgroup_del_lru_list(struct page *page, enum lru_list lru)
 {
 	struct page_cgroup *pc;
-	struct mem_cgroup *mem;
 	struct mem_cgroup_per_zone *mz;
 
 	if (mem_cgroup_disabled())
 		return;
 	pc = lookup_page_cgroup(page);
 	/* can happen while we handle swapcache. */
-	if (list_empty(&pc->lru) || !pc->mem_cgroup)
+	if (!TestClearPageCgroupAcctLRU(pc))
 		return;
+	VM_BUG_ON(!pc->mem_cgroup);
 	/*
 	 * We don't check PCG_USED bit. It's cleared when the "page" is finally
 	 * removed from global LRU.
 	 */
 	mz = page_cgroup_zoneinfo(pc);
-	mem = pc->mem_cgroup;
 	MEM_CGROUP_ZSTAT(mz, lru) -= 1;
+	if (mem_cgroup_is_root(pc->mem_cgroup))
+		return;
+	VM_BUG_ON(list_empty(&pc->lru));
 	list_del_init(&pc->lru);
 	return;
 }
@@ -410,8 +413,8 @@ void mem_cgroup_rotate_lru_list(struct page *page, enum lru_list lru)
 	 * For making pc->mem_cgroup visible, insert smp_rmb() here.
 	 */
 	smp_rmb();
-	/* unused page is not rotated. */
-	if (!PageCgroupUsed(pc))
+	/* unused or root page is not rotated. */
+	if (!PageCgroupUsed(pc) || PageCgroupAcctLRU(pc))
 		return;
 	mz = page_cgroup_zoneinfo(pc);
 	list_move(&pc->lru, &mz->lists[lru]);
@@ -425,6 +428,7 @@ void mem_cgroup_add_lru_list(struct page *page, enum lru_list lru)
 	if (mem_cgroup_disabled())
 		return;
 	pc = lookup_page_cgroup(page);
+	VM_BUG_ON(PageCgroupAcctLRU(pc));
 	/*
 	 * Used bit is set without atomic ops but after smp_wmb().
 	 * For making pc->mem_cgroup visible, insert smp_rmb() here.
@@ -435,6 +439,9 @@ void mem_cgroup_add_lru_list(struct page *page, enum lru_list lru)
 
 	mz = page_cgroup_zoneinfo(pc);
 	MEM_CGROUP_ZSTAT(mz, lru) += 1;
+	SetPageCgroupAcctLRU(pc);
+	if (mem_cgroup_is_root(pc->mem_cgroup))
+		return;
 	list_add(&pc->lru, &mz->lists[lru]);
 }
 
@@ -469,7 +476,7 @@ static void mem_cgroup_lru_add_after_commit_swapcache(struct page *page)
 
 	spin_lock_irqsave(&zone->lru_lock, flags);
 	/* link when the page is linked to LRU but page_cgroup isn't */
-	if (PageLRU(page) && list_empty(&pc->lru))
+	if (PageLRU(page) && !PageCgroupAcctLRU(pc))
 		mem_cgroup_add_lru_list(page, page_lru(page));
 	spin_unlock_irqrestore(&zone->lru_lock, flags);
 }
@@ -1106,9 +1113,22 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
 		css_put(&mem->css);
 		return;
 	}
+
 	pc->mem_cgroup = mem;
 	smp_wmb();
-	pc->flags = pcg_default_flags[ctype];
+	switch (ctype) {
+	case MEM_CGROUP_CHARGE_TYPE_CACHE:
+	case MEM_CGROUP_CHARGE_TYPE_SHMEM:
+		SetPageCgroupCache(pc);
+		SetPageCgroupUsed(pc);
+		break;
+	case MEM_CGROUP_CHARGE_TYPE_MAPPED:
+		ClearPageCgroupCache(pc);
+		SetPageCgroupUsed(pc);
+		break;
+	default:
+		break;
+	}
 
 	mem_cgroup_charge_statistics(mem, pc, true);
 
@@ -2047,6 +2067,10 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
 	name = MEMFILE_ATTR(cft->private);
 	switch (name) {
 	case RES_LIMIT:
+		if (mem_cgroup_is_root(memcg)) { /* Can't set limit on root */
+			ret = -EINVAL;
+			break;
+		}
 		/* This function does all necessary parse...reuse it */
 		ret = res_counter_memparse_write_strategy(buffer, &val);
 		if (ret)
@@ -2513,6 +2537,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
 	if (cont->parent == NULL) {
 		enable_swap_cgroup();
 		parent = NULL;
+		root_mem_cgroup = mem;
 	} else {
 		parent = mem_cgroup_from_cont(cont->parent);
 		mem->use_hierarchy = parent->use_hierarchy;
@@ -2541,6 +2566,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
 	return &mem->css;
 free_out:
 	__mem_cgroup_free(mem);
+	root_mem_cgroup = NULL;
 	return ERR_PTR(error);
 }
 
 
===


Thanks,
Daisuke Nishimura.

> 4. More LRU functions are aware of PageCgroupAcctLRU
> 
> Changelog v3 -> v2
> 
> 1. Rebase to mmotm 2nd June 2009
> 2. Test with some of the test cases recommended by Daisuke-San
> 
> Changelog v2 -> v1
> 1. Rebase to latest mmotm
> 
> This patch changes the memory cgroup and removes the overhead associated
> with accounting all pages in the root cgroup. As a side-effect, we can
> no longer set a memory hard limit in the root cgroup.
> 
> A new flag to track whether the page has been accounted or not
> has been added as well. Flags are now set atomically for page_cgroup,
> 
> Tests:
> 
> Results (for v2)
> 
> Obtained by
> 
> 1. Using tmpfs for mounting filesystem
> 2. Changing sync to be /bin/true (so that sync is not the bottleneck)
> 3. Used -s #cpus*40 -e #cpus*40
> 
> Reaim
> 		withoutpatch	patch
> AIM9		9532.48		9807.59
> dbase		19344.60	19285.71
> new_dbase	20101.65	20163.13
> shared		11827.77	11886.65
> compute		17317.38	17420.05
> 
> Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
> ---
> 
>  include/linux/page_cgroup.h |    5 ++++
>  mm/memcontrol.c             |   59 ++++++++++++++++++++++++++++++++++++-------
>  2 files changed, 54 insertions(+), 10 deletions(-)
> 
> 
> diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
> index 7339c7b..57c4d50 100644
> --- a/include/linux/page_cgroup.h
> +++ b/include/linux/page_cgroup.h
> @@ -26,6 +26,7 @@ enum {
>  	PCG_LOCK,  /* page cgroup is locked */
>  	PCG_CACHE, /* charged as cache */
>  	PCG_USED, /* this object is in use. */
> +	PCG_ACCT_LRU, /* page has been accounted for */
>  };
>  
>  #define TESTPCGFLAG(uname, lname)			\
> @@ -46,6 +47,10 @@ TESTPCGFLAG(Cache, CACHE)
>  TESTPCGFLAG(Used, USED)
>  CLEARPCGFLAG(Used, USED)
>  
> +SETPCGFLAG(AcctLRU, ACCT_LRU)
> +CLEARPCGFLAG(AcctLRU, ACCT_LRU)
> +TESTPCGFLAG(AcctLRU, ACCT_LRU)
> +
>  static inline int page_cgroup_nid(struct page_cgroup *pc)
>  {
>  	return page_to_nid(pc->page);
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 6ceb6f2..399d416 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -43,6 +43,7 @@
>  
>  struct cgroup_subsys mem_cgroup_subsys __read_mostly;
>  #define MEM_CGROUP_RECLAIM_RETRIES	5
> +struct mem_cgroup *root_mem_cgroup __read_mostly;
>  
>  #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
>  /* Turned on only when memory cgroup is enabled && really_do_swap_account = 1 */
> @@ -219,6 +220,11 @@ static void mem_cgroup_get(struct mem_cgroup *mem);
>  static void mem_cgroup_put(struct mem_cgroup *mem);
>  static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem);
>  
> +static inline bool mem_cgroup_is_root(struct mem_cgroup *mem)
> +{
> +	return (mem == root_mem_cgroup);
> +}
> +
>  static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
>  					 struct page_cgroup *pc,
>  					 bool charge)
> @@ -378,15 +384,25 @@ void mem_cgroup_del_lru_list(struct page *page, enum lru_list lru)
>  		return;
>  	pc = lookup_page_cgroup(page);
>  	/* can happen while we handle swapcache. */
> -	if (list_empty(&pc->lru) || !pc->mem_cgroup)
> +	mem = pc->mem_cgroup;
> +	if (!mem)
> +		return;
> +	if (mem_cgroup_is_root(mem)) {
> +		if (!PageCgroupAcctLRU(pc))
> +			return;
> +	} else if (list_empty(&pc->lru))
>  		return;
> +
>  	/*
>  	 * We don't check PCG_USED bit. It's cleared when the "page" is finally
>  	 * removed from global LRU.
>  	 */
>  	mz = page_cgroup_zoneinfo(pc);
> -	mem = pc->mem_cgroup;
>  	MEM_CGROUP_ZSTAT(mz, lru) -= 1;
> +	if (PageCgroupAcctLRU(pc)) {
> +		ClearPageCgroupAcctLRU(pc);
> +		return;
> +	}
>  	list_del_init(&pc->lru);
>  	return;
>  }
> @@ -410,8 +426,8 @@ void mem_cgroup_rotate_lru_list(struct page *page, enum lru_list lru)
>  	 * For making pc->mem_cgroup visible, insert smp_rmb() here.
>  	 */
>  	smp_rmb();
> -	/* unused page is not rotated. */
> -	if (!PageCgroupUsed(pc))
> +	/* unused or root page is not rotated. */
> +	if (!PageCgroupUsed(pc) || PageCgroupAcctLRU(pc))
>  		return;
>  	mz = page_cgroup_zoneinfo(pc);
>  	list_move(&pc->lru, &mz->lists[lru]);
> @@ -435,6 +451,10 @@ void mem_cgroup_add_lru_list(struct page *page, enum lru_list lru)
>  
>  	mz = page_cgroup_zoneinfo(pc);
>  	MEM_CGROUP_ZSTAT(mz, lru) += 1;
> +	if (mem_cgroup_is_root(pc->mem_cgroup)) {
> +		SetPageCgroupAcctLRU(pc);
> +		return;
> +	}
>  	list_add(&pc->lru, &mz->lists[lru]);
>  }
>  
> @@ -445,12 +465,15 @@ void mem_cgroup_add_lru_list(struct page *page, enum lru_list lru)
>   * it again. This function is only used to charge SwapCache. It's done under
>   * lock_page and expected that zone->lru_lock is never held.
>   */
> -static void mem_cgroup_lru_del_before_commit_swapcache(struct page *page)
> +static void mem_cgroup_lru_del_before_commit_swapcache(struct page *page,
> +							struct page_cgroup *pc)
>  {
>  	unsigned long flags;
>  	struct zone *zone = page_zone(page);
> -	struct page_cgroup *pc = lookup_page_cgroup(page);
>  
> +	if (!pc->mem_cgroup ||
> +		(!PageCgroupAcctLRU(pc) && mem_cgroup_is_root(pc->mem_cgroup)))
> +		return;
>  	spin_lock_irqsave(&zone->lru_lock, flags);
>  	/*
>  	 * Forget old LRU when this page_cgroup is *not* used. This Used bit
> @@ -461,12 +484,15 @@ static void mem_cgroup_lru_del_before_commit_swapcache(struct page *page)
>  	spin_unlock_irqrestore(&zone->lru_lock, flags);
>  }
>  
> -static void mem_cgroup_lru_add_after_commit_swapcache(struct page *page)
> +static void mem_cgroup_lru_add_after_commit_swapcache(struct page *page,
> +							struct page_cgroup *pc)
>  {
>  	unsigned long flags;
>  	struct zone *zone = page_zone(page);
> -	struct page_cgroup *pc = lookup_page_cgroup(page);
>  
> +	if (!pc->mem_cgroup ||
> +		(!PageCgroupAcctLRU(pc) && mem_cgroup_is_root(pc->mem_cgroup)))
> +		return;
>  	spin_lock_irqsave(&zone->lru_lock, flags);
>  	/* link when the page is linked to LRU but page_cgroup isn't */
>  	if (PageLRU(page) && list_empty(&pc->lru))
> @@ -478,8 +504,13 @@ static void mem_cgroup_lru_add_after_commit_swapcache(struct page *page)
>  void mem_cgroup_move_lists(struct page *page,
>  			   enum lru_list from, enum lru_list to)
>  {
> +	struct page_cgroup *pc = lookup_page_cgroup(page);
>  	if (mem_cgroup_disabled())
>  		return;
> +	smp_rmb();
> +	if (!pc->mem_cgroup ||
> +		(!PageCgroupAcctLRU(pc) && mem_cgroup_is_root(pc->mem_cgroup)))
> +		return;
>  	mem_cgroup_del_lru_list(page, from);
>  	mem_cgroup_add_lru_list(page, to);
>  }
> @@ -1114,6 +1145,7 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
>  		css_put(&mem->css);
>  		return;
>  	}
> +
>  	pc->mem_cgroup = mem;
>  	smp_wmb();
>  	pc->flags = pcg_default_flags[ctype];
> @@ -1418,9 +1450,10 @@ __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
>  	if (!ptr)
>  		return;
>  	pc = lookup_page_cgroup(page);
> -	mem_cgroup_lru_del_before_commit_swapcache(page);
> +	smp_rmb();
> +	mem_cgroup_lru_del_before_commit_swapcache(page, pc);
>  	__mem_cgroup_commit_charge(ptr, pc, ctype);
> -	mem_cgroup_lru_add_after_commit_swapcache(page);
> +	mem_cgroup_lru_add_after_commit_swapcache(page, pc);
>  	/*
>  	 * Now swap is on-memory. This means this page may be
>  	 * counted both as mem and swap....double count.
> @@ -2055,6 +2088,10 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
>  	name = MEMFILE_ATTR(cft->private);
>  	switch (name) {
>  	case RES_LIMIT:
> +		if (mem_cgroup_is_root(memcg)) { /* Can't set limit on root */
> +			ret = -EINVAL;
> +			break;
> +		}
>  		/* This function does all necessary parse...reuse it */
>  		ret = res_counter_memparse_write_strategy(buffer, &val);
>  		if (ret)
> @@ -2521,6 +2558,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>  	if (cont->parent == NULL) {
>  		enable_swap_cgroup();
>  		parent = NULL;
> +		root_mem_cgroup = mem;
>  	} else {
>  		parent = mem_cgroup_from_cont(cont->parent);
>  		mem->use_hierarchy = parent->use_hierarchy;
> @@ -2549,6 +2587,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>  	return &mem->css;
>  free_out:
>  	__mem_cgroup_free(mem);
> +	root_mem_cgroup = NULL;
>  	return ERR_PTR(error);
>  }
>  
> 
> -- 
> 	Balbir

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