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Sat, 17 Jun 2023 13:27:23 -0700 (PDT) Date: Sat, 17 Jun 2023 21:27:22 +0100 From: Lorenzo Stoakes To: Peter Xu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Matthew Wilcox , Andrea Arcangeli , John Hubbard , Mike Rapoport , David Hildenbrand , Vlastimil Babka , "Kirill A . Shutemov" , Andrew Morton , Mike Kravetz , James Houghton , Hugh Dickins Subject: Re: [PATCH 6/7] mm/gup: Accelerate thp gup even for "pages != NULL" Message-ID: References: <20230613215346.1022773-1-peterx@redhat.com> <20230613215346.1022773-7-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230613215346.1022773-7-peterx@redhat.com> X-Rspamd-Queue-Id: 397B31C0005 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: y9djq3oayhddgesez95sius7ftp4fhj9 X-HE-Tag: 1687033645-758319 X-HE-Meta: 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 olRrSwHX JzcoOyltXXpPQimLfR/XV+8ObYwcJKw1Y3fzmJlYlYSJNjL7/US7Fcu0MrdMyKyCWRTJXsBrkO4H02rLCfS40rpS9H7D+B1ul4e+Yv9ZO/XE5e+qZpDFdXfaCPheK4Hu423bHeZJBZyQdftB4ilXFgZEzDxHxEMRRgeLHuoqlhq2Ik63J7Zsr77m/GV+RQujNlPHdiTdd/GSYgA5kxaEyvjMI190f1o9FOJyXLOHJ3aDfzlFYD9V6UiNakTQ9oCsf6qBDwT+L8pBbhBdvbSL/3OJ8s3Fa5cPhoIZtxvvNw04Khnr/6KmAPqMN0U6ntZ6hkYjsuiIL9a8JIivC3V0rj5yxXTVM7fFejvfyssaM1WOIOKLwXFPolaLAhECogwhpneBJEl5Pt6Es5fXMvVYH4/CTbIemsBRrnBwPWy6ELE3LrSEeM0MjslVQfY1LsBdjm+EkwRoFGR8jyKvI/sc1EKqH1Q== 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 Tue, Jun 13, 2023 at 05:53:45PM -0400, Peter Xu wrote: > The acceleration of THP was done with ctx.page_mask, however it'll be > ignored if **pages is non-NULL. > > The old optimization was introduced in 2013 in 240aadeedc4a ("mm: > accelerate mm_populate() treatment of THP pages"). It didn't explain why > we can't optimize the **pages non-NULL case. It's possible that at that > time the major goal was for mm_populate() which should be enough back then. > > Optimize thp for all cases, by properly looping over each subpage, doing > cache flushes, and boost refcounts / pincounts where needed in one go. > > This can be verified using gup_test below: > > # chrt -f 1 ./gup_test -m 512 -t -L -n 1024 -r 10 > > Before: 13992.50 ( +-8.75%) > After: 378.50 (+-69.62%) > > Signed-off-by: Peter Xu > --- > mm/gup.c | 36 +++++++++++++++++++++++++++++------- > 1 file changed, 29 insertions(+), 7 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index a2d1b3c4b104..cdabc8ea783b 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -1210,16 +1210,38 @@ static long __get_user_pages(struct mm_struct *mm, > goto out; > } > next_page: > - if (pages) { > - pages[i] = page; > - flush_anon_page(vma, page, start); > - flush_dcache_page(page); > - ctx.page_mask = 0; > - } > - > page_increm = 1 + (~(start >> PAGE_SHIFT) & ctx.page_mask); > if (page_increm > nr_pages) > page_increm = nr_pages; > + > + if (pages) { > + struct page *subpage; > + unsigned int j; > + > + /* > + * This must be a large folio (and doesn't need to > + * be the whole folio; it can be part of it), do > + * the refcount work for all the subpages too. > + * Since we already hold refcount on the head page, > + * it should never fail. > + * > + * NOTE: here the page may not be the head page > + * e.g. when start addr is not thp-size aligned. > + */ > + if (page_increm > 1) > + WARN_ON_ONCE( > + try_grab_folio(compound_head(page), > + page_increm - 1, > + foll_flags) == NULL); I'm not sure this should be warning but otherwise ignoring this returning NULL? This feels like a case that could come up in realtiy, e.g. folio_ref_try_add_rcu() fails, or !folio_is_longterm_pinnable(). Side-note: I _hate_ the semantics of GUP such that try_grab_folio() (invoked, other than for huge page cases, by the GUP-fast logic) will explicitly fail if neither FOLL_GET or FOLL_PIN are specified, differentiating it from try_grab_page() in this respect. This is a side-note and not relevant here, as all callers to __get_user_pages() either explicitly set FOLL_GET if not set by user (in __get_user_pages_locked()) or don't set pages (e.g. in faultin_vma_page_range()) > + > + for (j = 0; j < page_increm; j++) { > + subpage = nth_page(page, j); > + pages[i+j] = subpage; > + flush_anon_page(vma, subpage, start + j * PAGE_SIZE); > + flush_dcache_page(subpage); > + } > + } > + > i += page_increm; > start += page_increm * PAGE_SIZE; > nr_pages -= page_increm; > -- > 2.40.1 >