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From: Alexander Duyck <alexander.duyck@gmail.com>
To: Alex Shi <alex.shi@linux.alibaba.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>,
	Michal Hocko <mhocko@kernel.org>,
	 Vladimir Davydov <vdavydov.dev@gmail.com>
Subject: Re: [PATCH v17 13/21] mm/lru: introduce TestClearPageLRU
Date: Wed, 5 Aug 2020 15:43:26 -0700
Message-ID: <CAKgT0Ud1+FkJcTXR0MxZYFxd7mr=opdXfXKTqkmiu4NNMyT4bg@mail.gmail.com> (raw)
In-Reply-To: <9b906469-38fb-8a4e-9a47-d617c7669579@linux.alibaba.com>

On Tue, Jul 28, 2020 at 8:53 PM Alex Shi <alex.shi@linux.alibaba.com> wrote:
>
> rewrite the commit log.
>
> From 9310c359b0049e3cc9827b771dc583d504bbf022 Mon Sep 17 00:00:00 2001
> From: Alex Shi <alex.shi@linux.alibaba.com>
> Date: Sat, 25 Apr 2020 12:03:30 +0800
> Subject: [PATCH v17 13/23] mm/lru: introduce TestClearPageLRU
>
> Currently lru_lock still guards both lru list and page's lru bit, that's
> ok. but if we want to use specific lruvec lock on the page, we need to
> pin down the page's lruvec/memcg during locking. Just taking lruvec
> lock first may be undermined by the page's memcg charge/migration. To
> fix this problem, we could clear the lru bit out of locking and use
> it as pin down action to block the page isolation in memcg changing.
>
> So now a standard steps of page isolation is following:
>         1, get_page();         #pin the page avoid to be free
>         2, TestClearPageLRU(); #block other isolation like memcg change
>         3, spin_lock on lru_lock; #serialize lru list access
>         4, delete page from lru list;
> The step 2 could be optimzed/replaced in scenarios which page is
> unlikely be accessed or be moved between memcgs.
>
> This patch start with the first part: TestClearPageLRU, which combines
> PageLRU check and ClearPageLRU into a macro func TestClearPageLRU. This
> function will be used as page isolation precondition to prevent other
> isolations some where else. Then there are may !PageLRU page on lru
> list, need to remove BUG() checking accordingly.
>
> There 2 rules for lru bit now:
> 1, the lru bit still indicate if a page on lru list, just in some
>    temporary moment(isolating), the page may have no lru bit when
>    it's on lru list.  but the page still must be on lru list when the
>    lru bit set.
> 2, have to remove lru bit before delete it from lru list.
>
> Hugh Dickins pointed that when a page is in free path and no one is
> possible to take it, non atomic lru bit clearing is better, like in
> __page_cache_release and release_pages.
> And no need get_page() before lru bit clear in isolate_lru_page,
> since it '(1) Must be called with an elevated refcount on the page'.
>
> As Andrew Morton mentioned this change would dirty cacheline for page
> isn't on LRU. But the lost would be acceptable with Rong Chen
> <rong.a.chen@intel.com> report:
> https://lkml.org/lkml/2020/3/4/173
>
> Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
> Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-kernel@vger.kernel.org
> Cc: cgroups@vger.kernel.org
> Cc: linux-mm@kvack.org
> ---
>  include/linux/page-flags.h |  1 +
>  mm/mlock.c                 |  3 +--
>  mm/swap.c                  |  6 ++----
>  mm/vmscan.c                | 18 +++++++-----------
>  4 files changed, 11 insertions(+), 17 deletions(-)
>

<snip>

> diff --git a/mm/swap.c b/mm/swap.c
> index f645965fde0e..5092fe9c8c47 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -83,10 +83,9 @@ static void __page_cache_release(struct page *page)
>                 struct lruvec *lruvec;
>                 unsigned long flags;
>
> +               __ClearPageLRU(page);
>                 spin_lock_irqsave(&pgdat->lru_lock, flags);
>                 lruvec = mem_cgroup_page_lruvec(page, pgdat);
> -               VM_BUG_ON_PAGE(!PageLRU(page), page);
> -               __ClearPageLRU(page);
>                 del_page_from_lru_list(page, lruvec, page_off_lru(page));
>                 spin_unlock_irqrestore(&pgdat->lru_lock, flags);
>         }
> @@ -878,9 +877,8 @@ void release_pages(struct page **pages, int nr)
>                                 spin_lock_irqsave(&locked_pgdat->lru_lock, flags);
>                         }
>
> -                       lruvec = mem_cgroup_page_lruvec(page, locked_pgdat);
> -                       VM_BUG_ON_PAGE(!PageLRU(page), page);
>                         __ClearPageLRU(page);
> +                       lruvec = mem_cgroup_page_lruvec(page, locked_pgdat);
>                         del_page_from_lru_list(page, lruvec, page_off_lru(page));
>                 }
>

The more I look at this piece it seems like this change wasn't really
necessary. If anything it seems like it could catch potential bugs as
it was testing for the PageLRU flag before and then clearing it
manually anyway. In addition it doesn't reduce the critical path by
any significant amount so I am not sure these changes are providing
any benefit.


  reply index

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 [this message]
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
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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