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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>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	 Jann Horn <jannh@google.com>
Subject: Re: [PATCH v17 21/21] mm/lru: revise the comments of lru_lock
Date: Thu, 6 Aug 2020 09:27:16 -0700
Message-ID: <CAKgT0UcARhDAVYkJAPe=P5XBfk9fdyGPx0S7rqhiLLhg3s62dQ@mail.gmail.com> (raw)
In-Reply-To: <a1c6a3a6-f8e3-7bb5-e881-216a4b57ae84@linux.alibaba.com>

On Wed, Aug 5, 2020 at 6:39 PM Alex Shi <alex.shi@linux.alibaba.com> wrote:
>
>
>
> 在 2020/8/4 下午10:29, Alexander Duyck 写道:
> > On Tue, Aug 4, 2020 at 3:04 AM Alex Shi <alex.shi@linux.alibaba.com> wrote:
> >>
> >>
> >>
> >> 在 2020/8/4 上午6:37, Alexander Duyck 写道:
> >>>>
> >>>>  shrink_inactive_list() also diverts any unevictable pages that it finds on the
> >>>> -inactive lists to the appropriate zone's unevictable list.
> >>>> +inactive lists to the appropriate node's unevictable list.
> >>>>
> >>>>  shrink_inactive_list() should only see SHM_LOCK'd pages that became SHM_LOCK'd
> >>>>  after shrink_active_list() had moved them to the inactive list, or pages mapped
> >>> Same here.
> >>
> >> lruvec is used per memcg per node actually, and it fallback to node if memcg disabled.
> >> So the comments are still right.
> >>
> >> And most of changes just fix from zone->lru_lock to pgdat->lru_lock change.
> >
> > Actually in my mind one thing that might work better would be to
> > explain what the lruvec is and where it resides. Then replace zone
> > with lruvec since that is really where the unevictable list resides.
> > Then it would be correct for both the memcg and pgdat case.
>
> Could you like to revise the doc as your thought?
> >
> >>>
> >>>> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> >>>> index 64ede5f150dc..44738cdb5a55 100644
> >>>> --- a/include/linux/mm_types.h
> >>>> +++ b/include/linux/mm_types.h
> >>>> @@ -78,7 +78,7 @@ struct page {
> >>>>                 struct {        /* Page cache and anonymous pages */
> >>>>                         /**
> >>>>                          * @lru: Pageout list, eg. active_list protected by
> >>>> -                        * pgdat->lru_lock.  Sometimes used as a generic list
> >>>> +                        * lruvec->lru_lock.  Sometimes used as a generic list
> >>>>                          * by the page owner.
> >>>>                          */
> >>>>                         struct list_head lru;
> >>>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> >>>> index 8af956aa13cf..c92289a4e14d 100644
> >>>> --- a/include/linux/mmzone.h
> >>>> +++ b/include/linux/mmzone.h
> >>>> @@ -115,7 +115,7 @@ static inline bool free_area_empty(struct free_area *area, int migratetype)
> >>>>  struct pglist_data;
> >>>>
> >>>>  /*
> >>>> - * zone->lock and the zone lru_lock are two of the hottest locks in the kernel.
> >>>> + * zone->lock and the lru_lock are two of the hottest locks in the kernel.
> >>>>   * So add a wild amount of padding here to ensure that they fall into separate
> >>>>   * cachelines.  There are very few zone structures in the machine, so space
> >>>>   * consumption is not a concern here.
> >>> So I don't believe you are using ZONE_PADDING in any way to try and
> >>> protect the LRU lock currently. At least you aren't using it in the
> >>> lruvec. As such it might make sense to just drop the reference to the
> >>> lru_lock here. That reminds me that we still need to review the
> >>> placement of the lru_lock and determine if there might be a better
> >>> placement and/or padding that might improve performance when under
> >>> heavy stress.
> >>>
> >>
> >> Right, is it the following looks better?
> >>
> >> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> >> index ccc76590f823..0ed520954843 100644
> >> --- a/include/linux/mmzone.h
> >> +++ b/include/linux/mmzone.h
> >> @@ -113,8 +113,7 @@ static inline bool free_area_empty(struct free_area *area, int migratetype)
> >>  struct pglist_data;
> >>
> >>  /*
> >> - * zone->lock and the lru_lock are two of the hottest locks in the kernel.
> >> - * So add a wild amount of padding here to ensure that they fall into separate
> >> + * Add a wild amount of padding here to ensure datas fall into separate
> >>   * cachelines.  There are very few zone structures in the machine, so space
> >>   * consumption is not a concern here.
> >>   */
> >>
> >> Thanks!
> >> Alex
> >
> > I would maybe tweak it to make sure it is clear that we are using this
> > to pad out items that are likely to cause cache thrash such as various
> > hot spinocks and such.
> >
>
> I appreciate if you like to change the doc better. :)

Give me a day or so. I will submit a follow-on patch with some cleanup
for the comments.

Thanks.

- Alex


  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
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 [this message]
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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