Messages in this thread | | | Subject | Re: [PATCH next] mm/swap.c: reduce lock contention in lru_cache_add | From | Vlastimil Babka <> | Date | Thu, 26 Nov 2020 16:44:04 +0100 |
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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); >> >
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