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

[KAMEZAWA Hiroyuki]

On Wed, 22 Jul 2009 17:28:43 +0900 (JST)
Ryo Tsuruta <ryov at valinux.co.jp> wrote:
> > But, following is more straightforward. (and what you do is not different
> > from this.)
> > ==
> > struct page {
> > 	.....
> > #ifdef CONFIG_BLOCKIO_CGROUP
> > 	void *blockio_cgroup;
> > #endif
> > }
> > ==
> 
> This increases the size of struct page. Could I get a consensus on
> this approach?
> 
Just God knows ;)

To be honest, what I expected in these days for people of blockio cgroup is like
following for getting room for themselves.

I'm now thinking to do this by myself and offer a room for you because
terrible bugs have been gone now and I have time.

Balbir, if you have no concerns, I'll clean up and send this to mmotm.
(maybe softlimit accesses pc->page and I have to update this.)

Note: This is _not_ tested at all.

Thanks,
-Kame
==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>

page cgroup has pointer to memmap it stands for.
But, page_cgroup->page is not accessed in fast path and not necessary
and not modified. Then, it's not to be maintained as pointer.

This patch removes "page" from page_cgroup and add
page_cgroup_to_page() function. This uses some amount of FLAGS bit
as struct page does.
As side effect, nid, zid can be obtaind from page_cgroup itself.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>
---
 include/linux/page_cgroup.h |   19 ++++++++++++++++---
 mm/page_cgroup.c            |   42 ++++++++++++++++++++++++++++++++----------
 2 files changed, 48 insertions(+), 13 deletions(-)

Index: mmotm-2.6.31-Jul16/include/linux/page_cgroup.h
===================================================================
--- mmotm-2.6.31-Jul16.orig/include/linux/page_cgroup.h
+++ mmotm-2.6.31-Jul16/include/linux/page_cgroup.h
@@ -13,7 +13,7 @@
 struct page_cgroup {
 	unsigned long flags;
 	struct mem_cgroup *mem_cgroup;
-	struct page *page;
+	/* block io tracking will use extra unsigned long bytes */
 	struct list_head lru;		/* per cgroup LRU list */
 };
 
@@ -32,7 +32,12 @@ static inline void __init page_cgroup_in
 #endif
 
 struct page_cgroup *lookup_page_cgroup(struct page *page);
+struct page *page_cgroup_to_page(struct page_cgroup *page);
 
+/*
+ * TOP MOST (NODE_SHIFT+ZONE_SHIFT or SECTION_SHIFT bits of "flags" are used
+ * for detecting pfn as struct page does.
+ */
 enum {
 	/* flags for mem_cgroup */
 	PCG_LOCK,  /* page cgroup is locked */
@@ -71,14 +76,22 @@ CLEARPCGFLAG(AcctLRU, ACCT_LRU)
 TESTPCGFLAG(AcctLRU, ACCT_LRU)
 TESTCLEARPCGFLAG(AcctLRU, ACCT_LRU)
 
+#ifdef NODE_NOT_IN_PAGE_FLAGS
 static inline int page_cgroup_nid(struct page_cgroup *pc)
 {
-	return page_to_nid(pc->page);
+	struct page *page= page_cgroup_to_page(pc);
+	return page_to_nid(page);
 }
+#else
+static inline int page_cgroup_nid(struct page_cgroup *pc)
+{
+	return (pc->flags >> NODES_PGSHIFT) & NODES_MASK;
+}
+#endif
 
 static inline enum zone_type page_cgroup_zid(struct page_cgroup *pc)
 {
-	return page_zonenum(pc->page);
+	return (pc->flags >> ZONEID_PGSHIFT) & ZONEID_MASK;
 }
 
 static inline void lock_page_cgroup(struct page_cgroup *pc)
Index: mmotm-2.6.31-Jul16/mm/page_cgroup.c
===================================================================
--- mmotm-2.6.31-Jul16.orig/mm/page_cgroup.c
+++ mmotm-2.6.31-Jul16/mm/page_cgroup.c
@@ -13,9 +13,12 @@
 static void __meminit
 __init_page_cgroup(struct page_cgroup *pc, unsigned long pfn)
 {
-	pc->flags = 0;
+	unsigned long flags;
+
 	pc->mem_cgroup = NULL;
-	pc->page = pfn_to_page(pfn);
+	/* Copy NODE/ZONE/SECTION information from struct page */
+	flags = pfn_to_page(pfn)->flags;
+	pc->flags = flags & ~((1 << __NR_PAGEFLAGS) - 1);
 	INIT_LIST_HEAD(&pc->lru);
 }
 static unsigned long total_usage;
@@ -42,6 +45,18 @@ struct page_cgroup *lookup_page_cgroup(s
 	return base + offset;
 }
 
+struct page *page_cgroup_to_page(struct page_cgroup *pc)
+{
+	int nid = (page->flags >> SECTIONS_PGSHIFT) & SECTIONS_MASK;
+	unsigned long pfn, offset;
+
+	offset = pc - NODE_DATA(nid)->node_page_cgroup
+	pfn = NODE_DATA(nid)->node_start_pfn + offset;
+
+	return pfn_to_page(pfn);
+}
+
+
 static int __init alloc_node_page_cgroup(int nid)
 {
 	struct page_cgroup *base, *pc;
@@ -104,6 +119,18 @@ struct page_cgroup *lookup_page_cgroup(s
 	return section->page_cgroup + pfn;
 }
 
+struct page *page_cgroup_to_page(struct page_cgroup *pc)
+{
+	unsigned long pfn, sectionid;
+	struct mem_section *section;
+
+	sectionid = (pc->flags >> SECTIONS_PGSHIFT) & SECTIONS_MASK;
+	section = __nr_to_section(sectionid);
+
+	pfn = pc - section->page_cgroup;
+	return pfn_to_page(pfn);
+}
+
 /* __alloc_bootmem...() is protected by !slab_available() */
 static int __init_refok init_section_page_cgroup(unsigned long pfn)
 {
@@ -128,15 +155,10 @@ static int __init_refok init_section_pag
 		}
 	} else {
 		/*
- 		 * We don't have to allocate page_cgroup again, but
-		 * address of memmap may be changed. So, we have to initialize
-		 * again.
+ 		 * We don't have to allocate page_cgroup again, and we don't
+		 * take care of address of memmap.
 		 */
-		base = section->page_cgroup + pfn;
-		table_size = 0;
-		/* check address of memmap is changed or not. */
-		if (base->page == pfn_to_page(pfn))
-			return 0;
+		return 0;
 	}
 
 	if (!base) {

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