Messages in this thread | | | From | Vlastimil Babka <> | Subject | Re: [PATCH next] mm/swap.c: reduce lock contention in lru_cache_add | Date | Thu, 26 Nov 2020 12:22:30 +0100 |
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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?
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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