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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>,
	Michal Hocko <mhocko@kernel.org>,
	Vladimir Davydov <vdavydov.dev@gmail.com>
Subject: Re: [PATCH v17 17/21] mm/lru: replace pgdat lru_lock with lruvec lock
Date: Tue, 28 Jul 2020 15:15:34 +0800
Message-ID: <49d2a784-3560-4d97-ece2-f2dfb6941495@linux.alibaba.com> (raw)
In-Reply-To: <CAKgT0UdaW4Rf43yULhQBuP07vQgmoPbaWHGKv1Z7fEPP6jH83w@mail.gmail.com>



在 2020/7/28 上午7:34, Alexander Duyck 写道:

>> @@ -847,11 +847,21 @@ static bool too_many_isolated(pg_data_t *pgdat)
>>                  * contention, to give chance to IRQs. Abort completely if
>>                  * a fatal signal is pending.
>>                  */
>> -               if (!(low_pfn % SWAP_CLUSTER_MAX)
>> -                   && compact_unlock_should_abort(&pgdat->lru_lock,
>> -                                           flags, &locked, cc)) {
>> -                       low_pfn = 0;
>> -                       goto fatal_pending;
>> +               if (!(low_pfn % SWAP_CLUSTER_MAX)) {
>> +                       if (locked_lruvec) {
>> +                               unlock_page_lruvec_irqrestore(locked_lruvec,
>> +                                                                       flags);
>> +                               locked_lruvec = NULL;
>> +                       }
>> +
>> +                       if (fatal_signal_pending(current)) {
>> +                               cc->contended = true;
>> +
>> +                               low_pfn = 0;
>> +                               goto fatal_pending;
>> +                       }
>> +
>> +                       cond_resched();
>>                 }
>>
>>                 if (!pfn_valid_within(low_pfn))
> 
> I'm noticing this patch introduces a bunch of noise. What is the
> reason for getting rid of compact_unlock_should_abort? It seems like
> you just open coded it here. If there is some sort of issue with it
> then it might be better to replace it as part of a preparatory patch
> before you introduce this one as changes like this make it harder to
> review.

Thanks for comments, Alex.

the func compact_unlock_should_abort should be removed since one of parameters
changed from 'bool *locked' to 'struct lruvec *lruvec'. So it's not applicable
now. I have to open it here instead of adding a only one user func.

> 
> It might make more sense to look at modifying
> compact_unlock_should_abort and compact_lock_irqsave (which always
> returns true so should probably be a void) to address the deficiencies
> they have that make them unusable for you.

I am wondering if people like a patch which just open compact_unlock_should_abort
func and move bool to void as a preparation patch, do you like this?


>> @@ -966,10 +975,20 @@ static bool too_many_isolated(pg_data_t *pgdat)
>>                 if (!TestClearPageLRU(page))
>>                         goto isolate_fail_put;
>>
>> +               rcu_read_lock();
>> +               lruvec = mem_cgroup_page_lruvec(page, pgdat);
>> +
>>                 /* If we already hold the lock, we can skip some rechecking */
>> -               if (!locked) {
>> -                       locked = compact_lock_irqsave(&pgdat->lru_lock,
>> -                                                               &flags, cc);
>> +               if (lruvec != locked_lruvec) {
>> +                       if (locked_lruvec)
>> +                               unlock_page_lruvec_irqrestore(locked_lruvec,
>> +                                                                       flags);
>> +
>> +                       compact_lock_irqsave(&lruvec->lru_lock, &flags, cc);
>> +                       locked_lruvec = lruvec;
>> +                       rcu_read_unlock();
>> +
>> +                       lruvec_memcg_debug(lruvec, page);
>>
>>                         /* Try get exclusive access under lock */
>>                         if (!skip_updated) {
> 
> So this bit makes things a bit complicated. From what I can can tell
> the comment about exclusive access under the lock is supposed to apply
> to the pageblock via the lru_lock. However you are having to retest
> the lock for each page because it is possible the page was moved to
> another memory cgroup while the lru_lock was released correct? So in

The pageblock is aligned by pfn, so pages in them maynot on same memcg
originally. and yes, page may be changed memcg also.

> this case is the lru vector lock really providing any protection for
> the skip_updated portion of this code block if the lock isn't
> exclusive to the pageblock? In theory this would probably make more
> sense to have protected the skip bits under the zone lock, but I
> imagine that was avoided due to the additional overhead.

when we change to lruvec->lru_lock, it does the same thing as pgdat->lru_lock.
just may get a bit more chance to here, and find out this is a skipable
pageblock and quit. 
Yes, logically, pgdat lru_lock seems better, but since we are holding lru_lock.
It's fine to not bother more locks.

> 
>> @@ -1876,6 +1876,12 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
>>                  *                                        list_add(&page->lru,)
>>                  *     list_add(&page->lru,) //corrupt
>>                  */
>> +               new_lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
>> +               if (new_lruvec != lruvec) {
>> +                       if (lruvec)
>> +                               spin_unlock_irq(&lruvec->lru_lock);
>> +                       lruvec = lock_page_lruvec_irq(page);
>> +               }
>>                 SetPageLRU(page);
>>
>>                 if (unlikely(put_page_testzero(page))) {
> 
> I was going through the code of the entire patch set and I noticed
> these changes in move_pages_to_lru. What is the reason for adding the
> new_lruvec logic? My understanding is that we are moving the pages to
> the lruvec provided are we not?If so why do we need to add code to get
> a new lruvec? The code itself seems to stand out from the rest of the
> patch as it is introducing new code instead of replacing existing
> locking code, and it doesn't match up with the description of what
> this function is supposed to do since it changes the lruvec.

A code here since some bugs happened. I will check it again anyway.

Thanks!


  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 [this message]
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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