On Wed 21-09-11 17:47:45, Johannes Weiner wrote:

On Wed, Sep 21, 2011 at 05:24:58PM +0200, Michal Hocko wrote:

quoted

On Mon 12-09-11 12:57:27, Johannes Weiner wrote:

[...]

quoted

quoted

@@ -934,115 +954,123 @@ EXPORT_SYMBOL(mem_cgroup_count_vm_event);
  * When moving account, the page is not on LRU. It's isolated.
  */
 
-struct page *mem_cgroup_lru_to_page(struct zone *zone, struct mem_cgroup *mem,
-				    enum lru_list lru)
+/**
+ * mem_cgroup_lru_add_list - account for adding an lru page and return lruvec
+ * @zone: zone of the page
+ * @page: the page
+ * @lru: current lru
+ *
+ * This function accounts for @page being added to @lru, and returns
+ * the lruvec for the given @zone and the memcg @page is charged to.
+ *
+ * The callsite is then responsible for physically linking the page to
+ * the returned lruvec->lists[@lru].
+ */
+struct lruvec *mem_cgroup_lru_add_list(struct zone *zone, struct page *page,
+				       enum lru_list lru)

I know that names are alway tricky but what about mem_cgroup_acct_lru_add?
Analogously for mem_cgroup_lru_del_list, mem_cgroup_lru_del and
mem_cgroup_lru_move_lists.

Hmm, but it doesn't just lru-account, it also looks up the right
lruvec for the caller to link the page to, so it's not necessarily an
improvement, although I agree that the name could be better.

Sorry, I do not have any better idea. I would just like if the name
didn't suggest that we actually modify the list.

quoted

quoted

@@ -3615,11 +3593,11 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
 static int mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
 				int node, int zid, enum lru_list lru)
 {
-	struct zone *zone;
 	struct mem_cgroup_per_zone *mz;
-	struct page_cgroup *pc, *busy;
 	unsigned long flags, loop;
 	struct list_head *list;
+	struct page *busy;
+	struct zone *zone;

Any specific reason to move zone declaration down here? Not that it
matters much. Just curious.

I find this arrangement more readable, I believe Ingo Molnar called it
the reverse christmas tree once :-).  Longest lines first, then sort
lines of equal length alphabetically.

And since it was basically complete, except for @zone, I just HAD to!

:)

quoted

quoted

@@ -3639,16 +3618,16 @@ static int mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
 			spin_unlock_irqrestore(&zone->lru_lock, flags);
 			break;
 		}
-		pc = list_entry(list->prev, struct page_cgroup, lru);
-		if (busy == pc) {
-			list_move(&pc->lru, list);
+		page = list_entry(list->prev, struct page, lru);
+		if (busy == page) {
+			list_move(&page->lru, list);
 			busy = NULL;
 			spin_unlock_irqrestore(&zone->lru_lock, flags);
 			continue;
 		}
 		spin_unlock_irqrestore(&zone->lru_lock, flags);
 
-		page = lookup_cgroup_page(pc);
+		pc = lookup_page_cgroup(page);

lookup_page_cgroup might return NULL so we probably want BUG_ON(!pc)
here. We are not very consistent about checking the return value,
though.

I think this is a myth and we should remove all those checks.  How can
pages circulate in userspace before they are fully onlined and their
page_cgroup buddies allocated?  In this case: how would they have been
charged in the first place and sit on a list without a list_head? :-)

Yes, that is right. This should never happen (last famous words). I can
imagine that a memory offlinening bug could cause issues.

Anyway the more appropriate way to handle that would BUG_ON directly in
lookup_page_cgroup.

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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