From: Alex Shi <alex.shi@linux.alibaba.com>
To: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Mel Gorman <mgorman@techsingularity.net>,
Tejun Heo <tj@kernel.org>, Hugh Dickins <hughd@google.com>,
Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
Daniel Jordan <daniel.m.jordan@oracle.com>,
Yang Shi <yang.shi@linux.alibaba.com>,
Matthew Wilcox <willy@infradead.org>,
Johannes Weiner <hannes@cmpxchg.org>,
kbuild test robot <lkp@intel.com>, linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
cgroups@vger.kernel.org, Shakeel Butt <shakeelb@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Wei Yang <richard.weiyang@gmail.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Rong Chen <rong.a.chen@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Andrey Ryabinin <aryabinin@virtuozzo.com>
Subject: Re: [PATCH v17 18/21] mm/lru: introduce the relock_page_lruvec function
Date: Thu, 30 Jul 2020 14:08:41 +0800 [thread overview]
Message-ID: <3345bfbf-ebe9-b5e0-a731-77dd7d76b0c9@linux.alibaba.com> (raw)
In-Reply-To: <CAKgT0UdFDcz=CQ+6mzcjh-apwy3UyPqAuOozvYr+2PSCNQrENA@mail.gmail.com>
在 2020/7/30 上午1:52, Alexander Duyck 写道:
>> + rcu_read_lock();
>> + locked = mem_cgroup_page_lruvec(page, pgdat) == locked_lruvec;
>> + rcu_read_unlock();
>> +
>> + if (locked)
>> + return locked_lruvec;
>> +
>> + if (locked_lruvec)
>> + unlock_page_lruvec_irqrestore(locked_lruvec, *flags);
>> +
>> + return lock_page_lruvec_irqsave(page, flags);
>> +}
>> +
> So looking these over they seem to be pretty inefficient for what they
> do. Basically in worst case (locked_lruvec == NULL) you end up calling
> mem_cgoup_page_lruvec and all the rcu_read_lock/unlock a couple times
> for a single page. It might make more sense to structure this like:
> if (locked_lruvec) {
Uh, we still need to check this page's lruvec, that needs a rcu_read_lock.
to save a mem_cgroup_page_lruvec call, we have to open lock_page_lruvec
as your mentained before.
> if (lruvec_holds_page_lru_lock(page, locked_lruvec))
> return locked_lruvec;
>
> unlock_page_lruvec_irqrestore(locked_lruvec, *flags);
> }
> return lock_page_lruvec_irqsave(page, flags);
>
> The other piece that has me scratching my head is that I wonder if we
> couldn't do this without needing the rcu_read_lock. For example, what
> if we were to compare the page mem_cgroup pointer to the memcg back
> pointer stored in the mem_cgroup_per_node? It seems like ordering
> things this way would significantly reduce the overhead due to the
> pointer chasing to see if the page is in the locked lruvec or not.
>
If page->mem_cgroup always be charged. the following could be better.
+/* Don't lock again iff page's lruvec locked */
+static inline struct lruvec *relock_page_lruvec_irqsave(struct page *page,
+ struct lruvec *locked_lruvec, unsigned long *flags)
+{
+ struct lruvec *lruvec;
+
+ if (mem_cgroup_disabled())
+ return locked_lruvec;
+
+ /* user page always be charged */
+ VM_BUG_ON_PAGE(!page->mem_cgroup, page);
+
+ rcu_read_lock();
+ if (likely(lruvec_memcg(locked_lruvec) == page->mem_cgroup)) {
+ rcu_read_unlock();
+ return locked_lruvec;
+ }
+
+ if (locked_lruvec)
+ unlock_page_lruvec_irqrestore(locked_lruvec, *flags);
+
+ lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
+ spin_lock_irqsave(&lruvec->lru_lock, *flags);
+ rcu_read_unlock();
+ lruvec_memcg_debug(lruvec, page);
+
+ return lruvec;
+}
+
The user page is always be charged since readahead page is charged now.
and looks we also can apply this patch. I will test it to see if there is
other exception.
commit 826128346e50f6c60c513e166998466b593becad
Author: Alex Shi <alex.shi@linux.alibaba.com>
Date: Thu Jul 30 13:58:38 2020 +0800
mm/memcg: remove useless check on page->mem_cgroup
Since readahead page will be charged on memcg too. We don't need to
check this exception now.
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index af96217f2ec5..0c7f6bed199b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1336,12 +1336,6 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgd
VM_BUG_ON_PAGE(PageTail(page), page);
memcg = READ_ONCE(page->mem_cgroup);
- /*
- * Swapcache readahead pages are added to the LRU - and
- * possibly migrated - before they are charged.
- */
- if (!memcg)
- memcg = root_mem_cgroup;
mz = mem_cgroup_page_nodeinfo(memcg, page);
lruvec = &mz->lruvec;
@@ -6962,10 +6956,7 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage)
if (newpage->mem_cgroup)
return;
- /* Swapcache readahead pages can get replaced before being charged */
memcg = oldpage->mem_cgroup;
- if (!memcg)
- return;
/* Force-charge the new page. The old one will be freed soon */
nr_pages = thp_nr_pages(newpage);
@@ -7160,10 +7151,6 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
memcg = page->mem_cgroup;
- /* Readahead page, never charged */
- if (!memcg)
- return;
-
/*
* In case the memcg owning these pages has been offlined and doesn't
* have an ID allocated to it anymore, charge the closest online
next prev parent reply other threads:[~2020-07-30 6:08 UTC|newest]
Thread overview: 102+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-25 12:59 [PATCH v17 00/21] per memcg lru lock Alex Shi
2020-07-25 12:59 ` [PATCH v17 01/21] mm/vmscan: remove unnecessary lruvec adding Alex Shi
2020-08-06 3:47 ` Alex Shi
2020-07-25 12:59 ` [PATCH v17 02/21] mm/page_idle: no unlikely double check for idle page counting Alex Shi
2020-07-25 12:59 ` [PATCH v17 03/21] mm/compaction: correct the comments of compact_defer_shift Alex Shi
2020-07-27 17:29 ` Alexander Duyck
2020-07-28 11:59 ` Alex Shi
2020-07-28 14:17 ` Alexander Duyck
2020-07-25 12:59 ` [PATCH v17 04/21] mm/compaction: rename compact_deferred as compact_should_defer Alex Shi
2020-07-25 12:59 ` [PATCH v17 05/21] mm/thp: move lru_add_page_tail func to huge_memory.c Alex Shi
2020-07-25 12:59 ` [PATCH v17 06/21] mm/thp: clean up lru_add_page_tail Alex Shi
2020-07-25 12:59 ` [PATCH v17 07/21] mm/thp: remove code path which never got into Alex Shi
2020-07-25 12:59 ` [PATCH v17 08/21] mm/thp: narrow lru locking Alex Shi
2020-07-25 12:59 ` [PATCH v17 09/21] mm/memcg: add debug checking in lock_page_memcg Alex Shi
2020-07-25 12:59 ` [PATCH v17 10/21] mm/swap: fold vm event PGROTATED into pagevec_move_tail_fn Alex Shi
2020-07-25 12:59 ` [PATCH v17 11/21] mm/lru: move lru_lock holding in func lru_note_cost_page Alex Shi
2020-08-05 21:18 ` Alexander Duyck
2020-07-25 12:59 ` [PATCH v17 12/21] mm/lru: move lock into lru_note_cost Alex Shi
2020-07-25 12:59 ` [PATCH v17 13/21] mm/lru: introduce TestClearPageLRU Alex Shi
2020-07-29 3:53 ` Alex Shi
2020-08-05 22:43 ` Alexander Duyck
2020-08-06 1:54 ` Alex Shi
2020-08-06 14:41 ` Alexander Duyck
2020-07-25 12:59 ` [PATCH v17 14/21] mm/compaction: do page isolation first in compaction Alex Shi
2020-08-04 21:35 ` Alexander Duyck
2020-08-06 18:38 ` Alexander Duyck
2020-08-07 3:24 ` Alex Shi
2020-08-07 14:51 ` Alexander Duyck
2020-08-10 13:10 ` Alex Shi
2020-08-10 14:41 ` Alexander Duyck
2020-08-11 8:22 ` Alex Shi
2020-08-11 14:47 ` Alexander Duyck
2020-08-12 11:43 ` Alex Shi
2020-08-12 12:16 ` Alex Shi
2020-08-12 16:51 ` Alexander Duyck
2020-08-13 1:46 ` Alex Shi
2020-08-13 2:17 ` Alexander Duyck
2020-08-13 3:52 ` Alex Shi
2020-08-13 4:02 ` [RFC PATCH 0/3] " Alexander Duyck
2020-08-13 4:02 ` [RFC PATCH 1/3] mm: Drop locked from isolate_migratepages_block Alexander Duyck
2020-08-13 6:56 ` Alex Shi
2020-08-13 14:32 ` Alexander Duyck
2020-08-14 7:25 ` Alex Shi
2020-08-13 7:44 ` Alex Shi
2020-08-13 14:26 ` Alexander Duyck
2020-08-13 4:02 ` [RFC PATCH 2/3] mm: Drop use of test_and_set_skip in favor of just setting skip Alexander Duyck
2020-08-14 7:19 ` Alex Shi
2020-08-14 14:24 ` Alexander Duyck
2020-08-14 21:15 ` Alexander Duyck
2020-08-15 9:49 ` Alex Shi
2020-08-17 15:38 ` Alexander Duyck
2020-08-18 6:50 ` Alex Shi
2020-08-13 4:02 ` [RFC PATCH 3/3] mm: Identify compound pages sooner in isolate_migratepages_block Alexander Duyck
2020-08-14 7:20 ` Alex Shi
2020-08-17 22:58 ` [PATCH v17 14/21] mm/compaction: do page isolation first in compaction Alexander Duyck
2020-07-25 12:59 ` [PATCH v17 15/21] mm/thp: add tail pages into lru anyway in split_huge_page() Alex Shi
2020-07-25 12:59 ` [PATCH v17 16/21] mm/swap: serialize memcg changes in pagevec_lru_move_fn Alex Shi
2020-07-25 12:59 ` [PATCH v17 17/21] mm/lru: replace pgdat lru_lock with lruvec lock Alex Shi
2020-07-27 23:34 ` Alexander Duyck
2020-07-28 7:15 ` Alex Shi
2020-07-28 11:19 ` Alex Shi
2020-07-28 14:54 ` Alexander Duyck
2020-07-29 1:00 ` Alex Shi
2020-07-29 1:27 ` Alexander Duyck
2020-07-29 2:27 ` Alex Shi
2020-07-28 15:39 ` Alex Shi
2020-07-28 15:55 ` Alexander Duyck
2020-07-29 0:48 ` Alex Shi
2020-07-29 3:54 ` Alex Shi
2020-08-06 7:41 ` Alex Shi
2020-07-25 12:59 ` [PATCH v17 18/21] mm/lru: introduce the relock_page_lruvec function Alex Shi
2020-07-29 17:52 ` Alexander Duyck
2020-07-30 6:08 ` Alex Shi [this message]
2020-07-31 14:20 ` Alexander Duyck
2020-07-31 21:14 ` [PATCH RFC] mm: Add function for testing if the current lruvec lock is valid alexander.h.duyck
2020-07-31 23:54 ` Alex Shi
2020-08-02 18:20 ` Alexander Duyck
2020-08-04 6:13 ` Alex Shi
2020-07-25 12:59 ` [PATCH v17 19/21] mm/vmscan: use relock for move_pages_to_lru Alex Shi
2020-08-03 22:49 ` Alexander Duyck
2020-08-04 6:23 ` Alex Shi
2020-07-25 12:59 ` [PATCH v17 20/21] mm/pgdat: remove pgdat lru_lock Alex Shi
2020-08-03 22:42 ` Alexander Duyck
2020-08-03 22:45 ` Alexander Duyck
2020-08-04 6:22 ` Alex Shi
2020-07-25 12:59 ` [PATCH v17 21/21] mm/lru: revise the comments of lru_lock Alex Shi
2020-08-03 22:37 ` Alexander Duyck
2020-08-04 10:04 ` Alex Shi
2020-08-04 14:29 ` Alexander Duyck
2020-08-06 1:39 ` Alex Shi
2020-08-06 16:27 ` Alexander Duyck
2020-07-27 5:40 ` [PATCH v17 00/21] per memcg lru lock Alex Shi
2020-07-29 14:49 ` Alex Shi
2020-07-29 18:06 ` Hugh Dickins
2020-07-30 2:16 ` Alex Shi
2020-08-03 15:07 ` Michal Hocko
2020-08-04 6:14 ` Alex Shi
2020-07-31 21:31 ` Alexander Duyck
2020-08-04 8:36 ` Alex Shi
2020-08-04 8:36 ` Alex Shi
2020-08-04 8:37 ` Alex Shi
2020-08-04 8:37 ` Alex Shi
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