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Wed, 25 Nov 2020 23:24:06 -0800 (PST) Date: Thu, 26 Nov 2020 00:24:02 -0700 From: Yu Zhao To: Alex Shi Cc: Konstantin Khlebnikov , Andrew Morton , Hugh Dickins , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH next] mm/swap.c: reduce lock contention in lru_cache_add Message-ID: <20201126072402.GA1047005@google.com> References: <1605860847-47445-1-git-send-email-alex.shi@linux.alibaba.com> <20201126045234.GA1014081@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Nov 26, 2020 at 02:39:03PM +0800, Alex Shi wrote: >=20 >=20 > =E5=9C=A8 2020/11/26 =E4=B8=8B=E5=8D=8812:52, Yu Zhao =E5=86=99=E9=81=93= : > >> */ > >> void __pagevec_lru_add(struct pagevec *pvec) > >> { > >> - int i; > >> - struct lruvec *lruvec =3D NULL; > >> + int i, nr_lruvec; > >> unsigned long flags =3D 0; > >> + struct page *page; > >> + struct lruvecs lruvecs; > >> =20 > >> - for (i =3D 0; i < pagevec_count(pvec); i++) { > >> - struct page *page =3D pvec->pages[i]; > >> + nr_lruvec =3D 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. > >=20 >=20 > With multiple memcgs, it do help a lot, I had gotten 30% grain on readt= wice > case. but yes, w/o MEMCG and NUMA, it's good to keep old behavior. So=20 > 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. 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; struct lruvec *lruvec =3D NULL; unsigned long flags =3D 0; =20 for (i =3D 0; i < pagevec_count(pvec); i++) { struct page *page =3D pvec->pages[i]; =20 + if (!page) + continue; + lruvec =3D relock_page_lruvec_irqsave(page, lruvec, &flags); - __pagevec_lru_add_fn(page, lruvec); + + for (j =3D i; j < pagevec_count(pvec); j++) { + if (page_to_nid(pvec->pages[j]) !=3D page_to_nid(page) || + page_memcg(pvec->pages[j]) !=3D page_memcg(page)) + continue; + + __pagevec_lru_add_fn(pvec->pages[j], lruvec); + pvec->pages[j] =3D NULL; + } } if (lruvec) unlock_page_lruvec_irqrestore(lruvec, flags);