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[192.55.52.120]) by mx.google.com with ESMTPS id o4si13945043pfb.274.2019.06.11.09.46.17 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 11 Jun 2019 09:46:17 -0700 (PDT) Received-SPF: pass (google.com: domain of ira.weiny@intel.com designates 192.55.52.120 as permitted sender) client-ip=192.55.52.120; Authentication-Results: mx.google.com; spf=pass (google.com: domain of ira.weiny@intel.com designates 192.55.52.120 as permitted sender) smtp.mailfrom=ira.weiny@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 11 Jun 2019 09:46:16 -0700 X-ExtLoop1: 1 Received: from iweiny-desk2.sc.intel.com ([10.3.52.157]) by FMSMGA003.fm.intel.com with ESMTP; 11 Jun 2019 09:46:16 -0700 Date: Tue, 11 Jun 2019 09:47:34 -0700 From: Ira Weiny To: Pingfan Liu Cc: John Hubbard , Andrew Morton , linux-mm@kvack.org, Mike Rapoport , Dan Williams , Matthew Wilcox , "Aneesh Kumar K.V" , Keith Busch , Christoph Hellwig , LKML Subject: Re: [PATCHv3 1/2] mm/gup: fix omission of check on FOLL_LONGTERM in get_user_pages_fast() Message-ID: <20190611164733.GA14336@iweiny-DESK2.sc.intel.com> References: <1559725820-26138-1-git-send-email-kernelfans@gmail.com> <20190605144912.f0059d4bd13c563ddb37877e@linux-foundation.org> <2b0a65ec-4fb0-430e-3e6a-b713fb5bb28f@nvidia.com> <20190611122935.GA9919@dhcp-128-55.nay.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190611122935.GA9919@dhcp-128-55.nay.redhat.com> User-Agent: Mutt/1.11.1 (2018-12-01) 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 11, 2019 at 08:29:35PM +0800, Pingfan Liu wrote: > On Fri, Jun 07, 2019 at 02:10:15PM +0800, Pingfan Liu wrote: > > On Fri, Jun 7, 2019 at 5:17 AM John Hubbard wrote: > > > > > > On 6/5/19 7:19 PM, Pingfan Liu wrote: > > > > On Thu, Jun 6, 2019 at 5:49 AM Andrew Morton wrote: > > > ... > > > >>> --- a/mm/gup.c > > > >>> +++ b/mm/gup.c > > > >>> @@ -2196,6 +2196,26 @@ static int __gup_longterm_unlocked(unsigned long start, int nr_pages, > > > >>> return ret; > > > >>> } > > > >>> > > > >>> +#ifdef CONFIG_CMA > > > >>> +static inline int reject_cma_pages(int nr_pinned, struct page **pages) > > > >>> +{ > > > >>> + int i; > > > >>> + > > > >>> + for (i = 0; i < nr_pinned; i++) > > > >>> + if (is_migrate_cma_page(pages[i])) { > > > >>> + put_user_pages(pages + i, nr_pinned - i); > > > >>> + return i; > > > >>> + } > > > >>> + > > > >>> + return nr_pinned; > > > >>> +} > > > >> > > > >> There's no point in inlining this. > > > > OK, will drop it in V4. > > > > > > > >> > > > >> The code seems inefficient. If it encounters a single CMA page it can > > > >> end up discarding a possibly significant number of non-CMA pages. I > > > > The trick is the page is not be discarded, in fact, they are still be > > > > referrenced by pte. We just leave the slow path to pick up the non-CMA > > > > pages again. > > > > > > > >> guess that doesn't matter much, as get_user_pages(FOLL_LONGTERM) is > > > >> rare. But could we avoid this (and the second pass across pages[]) by > > > >> checking for a CMA page within gup_pte_range()? > > > > It will spread the same logic to hugetlb pte and normal pte. And no > > > > improvement in performance due to slow path. So I think maybe it is > > > > not worth. > > > > > > > >> > > > > > > I think the concern is: for the successful gup_fast case with no CMA > > > pages, this patch is adding another complete loop through all the > > > pages. In the fast case. > > > > > > If the check were instead done as part of the gup_pte_range(), then > > > it would be a little more efficient for that case. > > > > > > As for whether it's worth it, *probably* this is too small an effect to measure. > > > But in order to attempt a measurement: running fio (https://github.com/axboe/fio) > > > with O_DIRECT on an NVMe drive, might shed some light. Here's an fio.conf file > > > that Jan Kara and Tom Talpey helped me come up with, for related testing: > > > > > > [reader] > > > direct=1 > > > ioengine=libaio > > > blocksize=4096 > > > size=1g > > > numjobs=1 > > > rw=read > > > iodepth=64 > > > > Unable to get a NVME device to have a test. And when testing fio on the > tranditional disk, I got the error "fio: engine libaio not loadable > fio: failed to load engine > fio: file:ioengines.c:89, func=dlopen, error=libaio: cannot open shared object file: No such file or directory" > > But I found a test case which can be slightly adjusted to met the aim. > It is tools/testing/selftests/vm/gup_benchmark.c > > Test enviroment: > MemTotal: 264079324 kB > MemFree: 262306788 kB > CmaTotal: 0 kB > CmaFree: 0 kB > on AMD EPYC 7601 > > Test command: > gup_benchmark -r 100 -n 64 > gup_benchmark -r 100 -n 64 -l > where -r stands for repeat times, -n is nr_pages param for > get_user_pages_fast(), -l is a new option to test FOLL_LONGTERM in fast > path, see a patch at the tail. Thanks! That is a good test to add. You should add the patch to the series. > > Test result: > w/o 477.800000 > w/o-l 481.070000 > a 481.800000 > a-l 640.410000 > b 466.240000 (question a: b outperforms w/o ?) > b-l 529.740000 > > Where w/o is baseline without any patch using v5.2-rc2, a is this series, b > does the check in gup_pte_range(). '-l' means FOLL_LONGTERM. > > I am suprised that b-l has about 17% improvement than a. (640.41 -529.74)/640.41 Wow that is bigger than I would have thought. I suspect it gets worse as -n increases? > > As for "question a: b outperforms w/o ?", I can not figure out why, maybe it can be > considered as variance. :-/ Does this change with larger -r or -n values? > > Based on the above result, I think it is better to do the check inside > gup_pte_range(). > > Any comment? I agree. Ira > > Thanks, > > > > Yeah, agreed. Data is more persuasive. Thanks for your suggestion. I > > will try to bring out the result. > > > > Thanks, > > Pingfan > > > > --- > Patch to do check inside gup_pte_range() > > diff --git a/mm/gup.c b/mm/gup.c > index 2ce3091..ba213a0 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -1757,6 +1757,10 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, > VM_BUG_ON(!pfn_valid(pte_pfn(pte))); > page = pte_page(pte); > > + if (unlikely(flags & FOLL_LONGTERM) && > + is_migrate_cma_page(page)) > + goto pte_unmap; > + > head = try_get_compound_head(page, 1); > if (!head) > goto pte_unmap; > @@ -1900,6 +1904,12 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, > refs++; > } while (addr += PAGE_SIZE, addr != end); > > + if (unlikely(flags & FOLL_LONGTERM) && > + is_migrate_cma_page(page)) { > + *nr -= refs; > + return 0; > + } > + > head = try_get_compound_head(pmd_page(orig), refs); > if (!head) { > *nr -= refs; > @@ -1941,6 +1951,12 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, > refs++; > } while (addr += PAGE_SIZE, addr != end); > > + if (unlikely(flags & FOLL_LONGTERM) && > + is_migrate_cma_page(page)) { > + *nr -= refs; > + return 0; > + } > + > head = try_get_compound_head(pud_page(orig), refs); > if (!head) { > *nr -= refs; > @@ -1978,6 +1994,12 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, > refs++; > } while (addr += PAGE_SIZE, addr != end); > > + if (unlikely(flags & FOLL_LONGTERM) && > + is_migrate_cma_page(page)) { > + *nr -= refs; > + return 0; > + } > + > head = try_get_compound_head(pgd_page(orig), refs); > if (!head) { > *nr -= refs; > --- > Patch for testing > > diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c > index 7dd602d..61dec5f 100644 > --- a/mm/gup_benchmark.c > +++ b/mm/gup_benchmark.c > @@ -6,8 +6,9 @@ > #include > > #define GUP_FAST_BENCHMARK _IOWR('g', 1, struct gup_benchmark) > -#define GUP_LONGTERM_BENCHMARK _IOWR('g', 2, struct gup_benchmark) > -#define GUP_BENCHMARK _IOWR('g', 3, struct gup_benchmark) > +#define GUP_FAST_LONGTERM_BENCHMARK _IOWR('g', 2, struct gup_benchmark) > +#define GUP_LONGTERM_BENCHMARK _IOWR('g', 3, struct gup_benchmark) > +#define GUP_BENCHMARK _IOWR('g', 4, struct gup_benchmark) > > struct gup_benchmark { > __u64 get_delta_usec; > @@ -53,6 +54,11 @@ static int __gup_benchmark_ioctl(unsigned int cmd, > nr = get_user_pages_fast(addr, nr, gup->flags & 1, > pages + i); > break; > + case GUP_FAST_LONGTERM_BENCHMARK: > + nr = get_user_pages_fast(addr, nr, > + (gup->flags & 1) | FOLL_LONGTERM, > + pages + i); > + break; > case GUP_LONGTERM_BENCHMARK: > nr = get_user_pages(addr, nr, > (gup->flags & 1) | FOLL_LONGTERM, > @@ -96,6 +102,7 @@ static long gup_benchmark_ioctl(struct file *filep, unsigned int cmd, > > switch (cmd) { > case GUP_FAST_BENCHMARK: > + case GUP_FAST_LONGTERM_BENCHMARK: > case GUP_LONGTERM_BENCHMARK: > case GUP_BENCHMARK: > break; > diff --git a/tools/testing/selftests/vm/gup_benchmark.c b/tools/testing/selftests/vm/gup_benchmark.c > index c0534e2..ade8acb 100644 > --- a/tools/testing/selftests/vm/gup_benchmark.c > +++ b/tools/testing/selftests/vm/gup_benchmark.c > @@ -15,8 +15,9 @@ > #define PAGE_SIZE sysconf(_SC_PAGESIZE) > > #define GUP_FAST_BENCHMARK _IOWR('g', 1, struct gup_benchmark) > -#define GUP_LONGTERM_BENCHMARK _IOWR('g', 2, struct gup_benchmark) > -#define GUP_BENCHMARK _IOWR('g', 3, struct gup_benchmark) > +#define GUP_FAST_LONGTERM_BENCHMARK _IOWR('g', 2, struct gup_benchmark) > +#define GUP_LONGTERM_BENCHMARK _IOWR('g', 3, struct gup_benchmark) > +#define GUP_BENCHMARK _IOWR('g', 4, struct gup_benchmark) > > struct gup_benchmark { > __u64 get_delta_usec; > @@ -37,7 +38,7 @@ int main(int argc, char **argv) > char *file = "/dev/zero"; > char *p; > > - while ((opt = getopt(argc, argv, "m:r:n:f:tTLUSH")) != -1) { > + while ((opt = getopt(argc, argv, "m:r:n:f:tTlLUSH")) != -1) { > switch (opt) { > case 'm': > size = atoi(optarg) * MB; > @@ -54,6 +55,9 @@ int main(int argc, char **argv) > case 'T': > thp = 0; > break; > + case 'l': > + cmd = GUP_FAST_LONGTERM_BENCHMARK; > + break; > case 'L': > cmd = GUP_LONGTERM_BENCHMARK; > break; > -- > 2.7.5 >