[Devel] [RFC][PATCH 1/3] Pagecache accounting

[Vaidyanathan Srinivasan]

Pagecache Accounting
--------------------

The rss accounting hooks have been generalised to handle both anon pages
and file backed pages and charge the resource counter.

Ref count has been added to page_container structure.  The ref count is used
to ensure a page is added or removed from page_container list only once
independent of repeated calls from pagecache, swapcache and mmap to RSS.

No setup patch is required since rss_limit and rss_usage has been generalised
as the resource counter for pagecache as well.

Signed-off-by: Vaidyanathan Srinivasan <svaidy at linux.vnet.ibm.com>
---
 include/linux/rss_container.h |   18 ++---
 mm/rss_container.c            |  134 ++++++++++++++++++++++++++++--------------
 2 files changed, 99 insertions(+), 53 deletions(-)

--- linux-2.6.22-rc2-mm1.orig/include/linux/rss_container.h
+++ linux-2.6.22-rc2-mm1/include/linux/rss_container.h
@@ -68,11 +68,11 @@ struct rss_container;
  *
  */

-int container_rss_prepare(struct page *, struct vm_area_struct *vma,
+int container_page_prepare(struct page *, struct mm_struct *mm,
 		struct page_container **);
-void container_rss_add(struct page_container *);
-void container_rss_del(struct page_container *);
-void container_rss_release(struct page_container *);
+void container_page_add(struct page_container *);
+void container_page_del(struct page_container *);
+void container_page_release(struct page_container *);

 void container_out_of_memory(struct rss_container *);

@@ -85,22 +85,22 @@ unsigned long isolate_pages_in_container
 		int order, int mode, struct zone *zone,
 		struct rss_container *, int active);
 #else
-static inline int container_rss_prepare(struct page *pg,
-		struct vm_area_struct *vma, struct page_container **pc)
+static inline int container_page_prepare(struct page *pg,
+		struct mm_struct *mm, struct page_container **pc)
 {
 	*pc = NULL; /* to make gcc happy */
 	return 0;
 }

-static inline void container_rss_add(struct page_container *pc)
+static inline void container_page_add(struct page_container *pc)
 {
 }

-static inline void container_rss_del(struct page_container *pc)
+static inline void container_page_del(struct page_container *pc)
 {
 }

-static inline void container_rss_release(struct page_container *pc)
+static inline void container_page_release(struct page_container *pc)
 {
 }

--- linux-2.6.22-rc2-mm1.orig/mm/rss_container.c
+++ linux-2.6.22-rc2-mm1/mm/rss_container.c
@@ -56,6 +56,9 @@ struct rss_container {
  */

 struct page_container {
+	unsigned long ref_cnt;  /* Ref cnt to keep track of
+				 * multiple additions of same page
+				 */
 	struct page *page;
 	struct rss_container *cnt;
 	struct list_head list; /* this is the element of (int)active_list of
@@ -93,26 +96,36 @@ void mm_free_container(struct mm_struct
  * I bet you have already read the comment in include/linux/rss_container.h :)
  */

-int container_rss_prepare(struct page *page, struct vm_area_struct *vma,
+int container_page_prepare(struct page *page, struct mm_struct *mm,
 		struct page_container **ppc)
 {
-	struct rss_container *rss;
-	struct page_container *pc;
-
-	rcu_read_lock();
-	rss = rcu_dereference(vma->vm_mm->rss_container);
-	css_get(&rss->css);
-	rcu_read_unlock();
-
-	pc = kmalloc(sizeof(struct page_container), GFP_KERNEL);
-	if (pc == NULL)
-		goto out_nomem;
+  	struct rss_container *rss;
+  	struct page_container *pc;
+ 	int rc = 1;
+
+  	/* Page may have been added to container earlier */
+  	pc = page_container(page);
+	/* Check if this is fist time addition or not */
+	if (!pc) {
+		rcu_read_lock();
+		rss = rcu_dereference(mm->rss_container);
+		css_get(&rss->css);
+		rcu_read_unlock();
+	} else {
+		rss = pc->cnt;
+	}

-	while (res_counter_charge(&rss->res, 1)) {
-		if (try_to_free_pages_in_container(rss)) {
-			atomic_inc(&rss->rss_reclaimed);
-			continue;
-		}
+ 	/* Charge the respective resource count first time only */
+ 	while (rc && !pc) {
+		rc = res_counter_charge(&rss->res, 1);
+
+ 		if (!rc)
+ 			break; /* All well */
+
+  		if (try_to_free_pages_in_container(rss)) {
+  			atomic_inc(&rss->rss_reclaimed);
+ 			continue; /* Try agin to charge container */
+  		}

 		/*
  		 * try_to_free_pages() might not give us a full picture
@@ -125,60 +138,93 @@ int container_rss_prepare(struct page *p
 		if (res_counter_check_under_limit(&rss->res))
 			continue;

-		container_out_of_memory(rss);
-		if (test_thread_flag(TIF_MEMDIE))
-			goto out_charge;
-	}
+ 		/* Unable to free memory?? */
+  		container_out_of_memory(rss);
+  		if (test_thread_flag(TIF_MEMDIE))
+  			goto out_charge;
+  	}
+
+  	/* First time addition to container: Create new page_container */
+  	if (!pc) {
+  		pc = kzalloc(sizeof(struct page_container), GFP_KERNEL);
+  		if (pc == NULL)
+  			goto out_nomem;
+
+ 		pc->page = page;
+ 		pc->cnt = rss;
+  	}

-	pc->page = page;
-	pc->cnt = rss;
-	*ppc = pc;
-	return 0;
+  	*ppc = pc;
+  	return 0;

 out_charge:
-	kfree(pc);
+ 	/* Need to zero page_container?? */
 out_nomem:
-	css_put(&rss->css);
-	return -ENOMEM;
+  	css_put(&rss->css);
+  	return -ENOMEM;
+
 }

-void container_rss_release(struct page_container *pc)
+void container_page_release(struct page_container *pc)
 {
 	struct rss_container *rss;

 	rss = pc->cnt;
-	res_counter_uncharge(&rss->res, 1);
-	css_put(&rss->css);
-	kfree(pc);
+	/* Setting the accounts right */
+	if (!pc->ref_cnt) {
+		res_counter_uncharge(&rss->res, 1);
+		set_page_container(pc->page, NULL);
+		kfree(pc);
+		css_put(&rss->css);
+	}
 }

-void container_rss_add(struct page_container *pc)
+void container_page_add(struct page_container *pc)
 {
 	struct page *pg;
 	struct rss_container *rss;
+	unsigned long irqflags;

 	pg = pc->page;
-	rss = pc->cnt;
+	if (pg == ZERO_PAGE(0))
+		return;

-	spin_lock_irq(&rss->res.lock);
-	list_add(&pc->list, &rss->active_list);
-	spin_unlock_irq(&rss->res.lock);
+	rss = pc->cnt;
+	spin_lock_irqsave(&rss->res.lock, irqflags);
+	if (!pc->ref_cnt)
+		list_add(&pc->list, &rss->inactive_list);
+	pc->ref_cnt++;
+	spin_unlock_irqrestore(&rss->res.lock, irqflags);

 	set_page_container(pg, pc);
 }

-void container_rss_del(struct page_container *pc)
+void container_page_del(struct page_container *pc)
 {
+	struct page *page;
 	struct rss_container *rss;
+	unsigned long irqflags;

+	page = pc->page;
 	rss = pc->cnt;
-	spin_lock_irq(&rss->res.lock);
-	list_del(&pc->list);
-	res_counter_uncharge_locked(&rss->res, 1);
-	spin_unlock_irq(&rss->res.lock);

-	css_put(&rss->css);
-	kfree(pc);
+	if (page == ZERO_PAGE(0))
+		return;
+
+	spin_lock_irqsave(&rss->res.lock, irqflags);
+	pc->ref_cnt--;
+	if (!pc->ref_cnt) {
+		list_del(&pc->list);
+		set_page_container(page, NULL);
+	}
+	spin_unlock_irqrestore(&rss->res.lock, irqflags);
+
+	if (!pc->ref_cnt) {
+		res_counter_uncharge(&rss->res, 1);
+		kfree(pc);
+		css_put(&rss->css);
+	}
+
 }

 /*