Re: + thp-compound_trans_order.patch added to -mm tree

[Andrea Arcangeli <aarcange@redhat.com>]

Hello Andrew,

here an incremental cleanup for this patch (it'd become
thp-compound_trans_order-fix.patch):

=====
Subject: thp: memcg: remove unnecessary compound_trans_order

From: Andrea Arcangeli <aarcange@redhat.com>

In these places PageTransHuge must not go away under memcg, as the page is
owned by the thread handling it. Add VM_BUG_ON and remove a superflous
page_size variable.

compound_trans_order for now remains for memory-failure.c, which later has to
be fixed to implement a safe compound_head too, that isn't safe right now.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1027,10 +1027,6 @@ mem_cgroup_get_reclaim_stat_from_page(st
 {
 	struct page_cgroup *pc;
 	struct mem_cgroup_per_zone *mz;
-	int page_size = PAGE_SIZE;
-
-	if (PageTransHuge(page))
-		page_size <<= compound_trans_order(page);
 
 	if (mem_cgroup_disabled())
 		return NULL;
@@ -2287,8 +2283,10 @@ static int mem_cgroup_charge_common(stru
 	int ret;
 	int page_size = PAGE_SIZE;
 
-	if (PageTransHuge(page))
-		page_size <<= compound_trans_order(page);
+	if (PageTransHuge(page)) {
+		page_size <<= compound_order(page);
+		VM_BUG_ON(!PageTransHuge(page));
+	}
 
 	pc = lookup_page_cgroup(page);
 	/* can happen at boot */
@@ -2559,8 +2557,10 @@ __mem_cgroup_uncharge_common(struct page
 	if (PageSwapCache(page))
 		return NULL;
 
-	if (PageTransHuge(page))
-		page_size <<= compound_trans_order(page);
+	if (PageTransHuge(page)) {
+		page_size <<= compound_order(page);
+		VM_BUG_ON(!PageTransHuge(page));
+	}
 
 	count = page_size >> PAGE_SHIFT;
 	/*


On Wed, Dec 15, 2010 at 03:58:21PM -0800, Andrew Morton wrote:
> 
> The patch titled
>      thp: compound_trans_order
> has been added to the -mm tree.  Its filename is
>      thp-compound_trans_order.patch
> 

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