From: Vlastimil Babka <vbabka@suse.cz>
To: Yu Zhao <yuzhao@google.com>,
Alex Shi <alex.shi@linux.alibaba.com>,
Matthew Wilcox <willy@infradead.org>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>, Michal Hocko <mhocko@suse.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH next] mm/swap.c: reduce lock contention in lru_cache_add
Date: Thu, 26 Nov 2020 16:44:04 +0100 [thread overview]
Message-ID: <c3d53633-af28-79c1-f42c-d5b851af4d56@suse.cz> (raw)
In-Reply-To: <464fa387-9dfd-a8c7-3d86-040f26fd4115@suse.cz>
On 11/26/20 12:22 PM, Vlastimil Babka wrote:
> On 11/26/20 8:24 AM, Yu Zhao wrote:
>> On Thu, Nov 26, 2020 at 02:39:03PM +0800, Alex Shi wrote:
>>>
>>>
>>> 在 2020/11/26 下午12:52, Yu Zhao 写道:
>>> >> */
>>> >> void __pagevec_lru_add(struct pagevec *pvec)
>>> >> {
>>> >> - int i;
>>> >> - struct lruvec *lruvec = NULL;
>>> >> + int i, nr_lruvec;
>>> >> unsigned long flags = 0;
>>> >> + struct page *page;
>>> >> + struct lruvecs lruvecs;
>>> >>
>>> >> - for (i = 0; i < pagevec_count(pvec); i++) {
>>> >> - struct page *page = pvec->pages[i];
>>> >> + nr_lruvec = sort_page_lruvec(&lruvecs, pvec);
>>> > Simply looping pvec multiple times (15 at most) for different lruvecs
>>> > would be better because 1) it requires no extra data structures and
>>> > therefore has better cache locality (theoretically faster) 2) it only
>>> > loops once when !CONFIG_MEMCG and !CONFIG_NUMA and therefore has no
>>> > impact on Android and Chrome OS.
>>> >
>>>
>>> With multiple memcgs, it do help a lot, I had gotten 30% grain on readtwice
>>> case. but yes, w/o MEMCG and NUMA, it's good to keep old behavior. So
>>> would you like has a proposal for this?
>>
>> Oh, no, I'm not against your idea. I was saying it doesn't seem
>> necessary to sort -- a nested loop would just do the job given
>> pagevec is small.
>
> Yeah that could work. The worst case doesn't look nice (O(n^2)) but it should be
> rather rare to have pages from really multiple memcgs/nodes?
However, Matthew wanted to increase pagevec size [1] and once 15^2 becomes 63^2,
it starts to be somewhat more worrying.
[1] https://lore.kernel.org/linux-mm/20201105172651.2455-1-willy@infradead.org/
> Maybe with the following change? Avoids going through the nulls if we got lucky
> (or have !MEMCG !NUMA).
>
>> diff --git a/mm/swap.c b/mm/swap.c
>> index cb3794e13b48..1d238edc2907 100644
>> --- a/mm/swap.c
>> +++ b/mm/swap.c
>> @@ -996,15 +996,26 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec)
>> */
>> void __pagevec_lru_add(struct pagevec *pvec)
>> {
>> - int i;
>> + int i, j;
>
> int i, j, n;
>
>> struct lruvec *lruvec = NULL;
>> unsigned long flags = 0;
>>
>
> n = pagevec_count(pvec);
>> for (i = 0; i < pagevec_count(pvec); i++) {
>
> for (i = 0; n; i++) {
>
>> struct page *page = pvec->pages[i];
>>
>> + if (!page)
>> + continue;
>> +
>> lruvec = relock_page_lruvec_irqsave(page, lruvec, &flags);
>> - __pagevec_lru_add_fn(page, lruvec);
>
> n--;
>
>> +
>> + for (j = i; j < pagevec_count(pvec); j++) {
>> + if (page_to_nid(pvec->pages[j]) != page_to_nid(page) ||
>> + page_memcg(pvec->pages[j]) != page_memcg(page))
>> + continue;
>> +
>> + __pagevec_lru_add_fn(pvec->pages[j], lruvec);
>> + pvec->pages[j] = NULL;
>
> n--;
>> + }
>> }
>> if (lruvec)
>> unlock_page_lruvec_irqrestore(lruvec, flags);
>>
>
next prev parent reply other threads:[~2020-11-26 15:44 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-20 8:27 [PATCH next] mm/swap.c: reduce lock contention in lru_cache_add Alex Shi
2020-11-20 23:19 ` Andrew Morton
2020-11-23 4:46 ` Alex Shi
2020-11-25 15:38 ` Vlastimil Babka
2020-11-26 3:12 ` Alex Shi
2020-11-26 11:05 ` Vlastimil Babka
2020-11-26 4:52 ` Yu Zhao
2020-11-26 6:39 ` Alex Shi
2020-11-26 7:24 ` Yu Zhao
2020-11-26 8:09 ` Alex Shi
2020-11-26 11:22 ` Vlastimil Babka
2020-11-26 15:44 ` Vlastimil Babka [this message]
2020-11-26 15:55 ` Matthew Wilcox
2020-11-27 3:14 ` Alex Shi
2020-12-01 8:02 ` [PATCH 1/3] mm/swap.c: pre-sort pages in pagevec for pagevec_lru_move_fn Alex Shi
2020-12-01 8:02 ` [PATCH 2/3] mm/swap.c: bail out early for no memcg and no numa Alex Shi
2020-12-01 8:02 ` [PATCH 3/3] mm/swap.c: extend the usage to pagevec_lru_add Alex Shi
2020-12-01 8:10 ` [PATCH 1/3] mm/swap.c: pre-sort pages in pagevec for pagevec_lru_move_fn Michal Hocko
2020-12-01 8:20 ` Alex Shi
2020-12-25 9:59 ` [RFC PATCH 0/4] pre sort pages on lruvec in pagevec Alex Shi
2020-12-25 9:59 ` [RFC PATCH 1/4] mm/swap.c: pre-sort pages in pagevec for pagevec_lru_move_fn Alex Shi
2020-12-25 9:59 ` [RFC PATCH 2/4] mm/swap.c: bail out early for no memcg and no numa Alex Shi
2020-12-25 9:59 ` [RFC PATCH 3/4] mm/swap.c: extend the usage to pagevec_lru_add Alex Shi
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