linux-kernel - [patch 6/7] mm: memcg: remove unneeded checks from newpage

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Date:	Tue, 29 Nov 2011 11:52:04 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>,
	Balbir Singh <bsingharora@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Hugh Dickins <hughd@...gle.com>, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [patch 6/7] mm: memcg: remove unneeded checks from newpage_charge()

From: Johannes Weiner <jweiner@...hat.com>

All callsites pass in freshly allocated pages and a valid mm.  As a
result, all checks pertaining the page's mapcount, page->mapping or
the fallback to init_mm are unneeded.

Signed-off-by: Johannes Weiner <jweiner@...hat.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Acked-by: Michal Hocko <mhocko@...e.cz>
---
 mm/memcontrol.c |   16 ++++------------
 1 files changed, 4 insertions(+), 12 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8ccb342..f5aa1b8 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2679,19 +2679,11 @@ int mem_cgroup_newpage_charge(struct page *page,
 {
 	if (mem_cgroup_disabled())
 		return 0;
-	/*
-	 * If already mapped, we don't have to account.
-	 * If page cache, page->mapping has address_space.
-	 * But page->mapping may have out-of-use anon_vma pointer,
-	 * detecit it by PageAnon() check. newly-mapped-anon's page->mapping
-	 * is NULL.
-  	 */
-	if (page_mapped(page) || (page->mapping && !PageAnon(page)))
-		return 0;
-	if (unlikely(!mm))
-		mm = &init_mm;
+	VM_BUG_ON(page_mapped(page));
+	VM_BUG_ON(page->mapping && !PageAnon(page));
+	VM_BUG_ON(!mm);
 	return mem_cgroup_charge_common(page, mm, gfp_mask,
-				MEM_CGROUP_CHARGE_TYPE_MAPPED);
+					MEM_CGROUP_CHARGE_TYPE_MAPPED);
 }
 
 static void
-- 
1.7.6.4

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