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From: Johannes Weiner <hannes@cmpxchg.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Alex Shi <alex.shi@linux.alibaba.com>,
	Joonsoo Kim <js1304@gmail.com>,
	Shakeel Butt <shakeelb@google.com>,
	Hugh Dickins <hughd@google.com>, Michal Hocko <mhocko@suse.com>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Roman Gushchin <guro@fb.com>,
	linux-mm@kvack.org, cgroups@vger.kernel.org,
	linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: [PATCH 19/19] mm: memcontrol: update page->mem_cgroup stability rules
Date: Fri,  8 May 2020 14:31:06 -0400	[thread overview]
Message-ID: <20200508183105.225460-20-hannes@cmpxchg.org> (raw)
In-Reply-To: <20200508183105.225460-1-hannes@cmpxchg.org>

The previous patches have simplified the access rules around
page->mem_cgroup somewhat:

1. We never change page->mem_cgroup while the page is isolated by
   somebody else. This was by far the biggest exception to our rules
   and it didn't stop at lock_page() or lock_page_memcg().

2. We charge pages before they get put into page tables now, so the
   somewhat fishy rule about "can be in page table as long as it's
   still locked" is now gone and boiled down to having an exclusive
   reference to the page.

Document the new rules. Any of the following will stabilize the
page->mem_cgroup association:

- the page lock
- LRU isolation
- lock_page_memcg()
- exclusive access to the page

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Alex Shi <alex.shi@linux.alibaba.com>
Reviewed-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
---
 mm/memcontrol.c | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 491fdeec0ce4..865440e8438e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1201,9 +1201,8 @@ int mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
  * @page: the page
  * @pgdat: pgdat of the page
  *
- * This function is only safe when following the LRU page isolation
- * and putback protocol: the LRU lock must be held, and the page must
- * either be PageLRU() or the caller must have isolated/allocated it.
+ * This function relies on page->mem_cgroup being stable - see the
+ * access rules in commit_charge().
  */
 struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgdat)
 {
@@ -2605,18 +2604,12 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg)
 {
 	VM_BUG_ON_PAGE(page->mem_cgroup, page);
 	/*
-	 * Nobody should be changing or seriously looking at
-	 * page->mem_cgroup at this point:
-	 *
-	 * - the page is uncharged
-	 *
-	 * - the page is off-LRU
-	 *
-	 * - an anonymous fault has exclusive page access, except for
-	 *   a locked page table
+	 * Any of the following ensures page->mem_cgroup stability:
 	 *
-	 * - a page cache insertion, a swapin fault, or a migration
-	 *   have the page locked
+	 * - the page lock
+	 * - LRU isolation
+	 * - lock_page_memcg()
+	 * - exclusive reference
 	 */
 	page->mem_cgroup = memcg;
 }
-- 
2.26.2



  parent reply	other threads:[~2020-05-08 18:33 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-08 18:30 [PATCH 00/19 V2] mm: memcontrol: charge swapin pages on instantiation Johannes Weiner
2020-05-08 18:30 ` [PATCH 01/19] mm: fix NUMA node file count error in replace_page_cache() Johannes Weiner
2020-05-18 11:18   ` Balbir Singh
2020-05-08 18:30 ` [PATCH 02/19] mm: memcontrol: fix stat-corrupting race in charge moving Johannes Weiner
2020-05-08 18:30 ` [PATCH 03/19] mm: memcontrol: drop @compound parameter from memcg charging API Johannes Weiner
2020-05-08 18:30 ` [PATCH 04/19] mm: memcontrol: move out cgroup swaprate throttling Johannes Weiner
2020-05-08 18:30 ` [PATCH 05/19] mm: memcontrol: convert page cache to a new mem_cgroup_charge() API Johannes Weiner
2020-06-10 16:09   ` Michal Hocko
2020-05-08 18:30 ` [PATCH 06/19] mm: memcontrol: prepare uncharging for removal of private page type counters Johannes Weiner
2020-05-08 18:30 ` [PATCH 07/19] mm: memcontrol: prepare move_account " Johannes Weiner
2020-05-08 18:30 ` [PATCH 08/19] mm: memcontrol: prepare cgroup vmstat infrastructure for native anon counters Johannes Weiner
2020-05-08 18:30 ` [PATCH 09/19] mm: memcontrol: switch to native NR_FILE_PAGES and NR_SHMEM counters Johannes Weiner
2020-06-10 16:42   ` Michal Hocko
2020-05-08 18:30 ` [PATCH 10/19] mm: memcontrol: switch to native NR_ANON_MAPPED counter Johannes Weiner
2020-05-08 18:30 ` [PATCH 11/19] mm: memcontrol: switch to native NR_ANON_THPS counter Johannes Weiner
2020-05-08 18:30 ` [PATCH 12/19] mm: memcontrol: convert anon and file-thp to new mem_cgroup_charge() API Johannes Weiner
2020-05-12 14:38   ` Qian Cai
2020-05-12 17:11     ` Qian Cai
2020-05-12 21:58     ` Johannes Weiner
2020-05-12 23:58       ` Qian Cai
2020-05-08 18:31 ` [PATCH 13/19] mm: memcontrol: drop unused try/commit/cancel charge API Johannes Weiner
2020-06-22 17:06   ` Ben Widawsky
2020-05-08 18:31 ` [PATCH 14/19] mm: memcontrol: prepare swap controller setup for integration Johannes Weiner
2020-05-08 18:31 ` [PATCH 15/19] mm: memcontrol: make swap tracking an integral part of memory control Johannes Weiner
2020-05-08 18:31 ` [PATCH 16/19] mm: memcontrol: charge swapin pages on instantiation Johannes Weiner
2020-06-11  9:35   ` Michal Hocko
2020-06-17  8:49     ` [PATCH for 5.8] mm: do_swap_page fix up the error code instantiation Michal Hocko
2020-06-17  9:02       ` Michal Hocko
2020-06-17 13:34         ` Johannes Weiner
2020-05-08 18:31 ` [PATCH 17/19] mm: memcontrol: document the new swap control behavior Johannes Weiner
2020-05-08 18:31 ` [PATCH 18/19] mm: memcontrol: delete unused lrucare handling Johannes Weiner
2020-05-08 18:31 ` Johannes Weiner [this message]
2020-06-11  9:40   ` [PATCH 19/19] mm: memcontrol: update page->mem_cgroup stability rules Michal Hocko
2020-05-13 11:30 ` [PATCH 00/19 V2] mm: memcontrol: charge swapin pages on instantiation Balbir Singh
2020-05-13 12:35   ` Johannes Weiner
2020-05-14 11:04     ` Balbir Singh

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