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[209.85.220.65]) by mx.google.com with SMTPS id t24sor2994097iom.11.2019.05.31.03.41.09 for (Google Transport Security); Fri, 31 May 2019 03:41:09 -0700 (PDT) Received-SPF: pass (google.com: domain of kernelfans@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=XGkP53Ss; spf=pass (google.com: domain of kernelfans@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=kernelfans@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=f7K/6YQSxV880DkgJ09eg6h5iBlyiK20sdzcSTZG0aM=; b=XGkP53SshfAPmjGlZUh6RXC8I0N9LNtD1Gjnv7hElsZCRY70TqFTw5zLekprBErZVZ kWW0cxpj4Vk8TtbhgL2/m+oJDO93uQmRsgY/3PUAHt72ui+eu+8iMoi0sbO9zp5mjhfA 1GujwFE4vKK3kFHn8SsgGZLlVsT8v4F/yInGr08a92cncLzgqLyq6eBfsYPsWvYCZ0Ih Zwia03Ei1sgEs8sRg0TKkx6I68y9yoOrNuuq1r2Ve5+NvzhE/6WwPZedH24GZrPPwrEj U+tPejHGcQjYBJptZNJZri0w0gnND+Gb+fk6g/Kx+1B2BKjDwxaCQbbHjB796JljRktB FTLg== X-Google-Smtp-Source: APXvYqyXE1xefJ2rEEvK1/15mQpuixTmPfm9Ib8UnCkKZn3rkf3o8/n4IOBDBtlTAiwv3kEYQXoYI4jiTop8Ywfoefc= X-Received: by 2002:a6b:e005:: with SMTP id z5mr4968657iog.161.1559299269094; Fri, 31 May 2019 03:41:09 -0700 (PDT) MIME-Version: 1.0 References: <1559170444-3304-1-git-send-email-kernelfans@gmail.com> <20190530214726.GA14000@iweiny-DESK2.sc.intel.com> <1497636a-8658-d3ff-f7cd-05230fdead19@nvidia.com> <20190530235307.GA28605@iweiny-DESK2.sc.intel.com> In-Reply-To: <20190530235307.GA28605@iweiny-DESK2.sc.intel.com> From: Pingfan Liu Date: Fri, 31 May 2019 18:40:57 +0800 Message-ID: Subject: Re: [PATCH] mm/gup: fix omission of check on FOLL_LONGTERM in get_user_pages_fast() To: Ira Weiny Cc: John Hubbard , linux-mm@kvack.org, Andrew Morton , Mike Rapoport , Dan Williams , Matthew Wilcox , "Aneesh Kumar K.V" , Keith Busch , LKML Content-Type: text/plain; charset="UTF-8" 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 Fri, May 31, 2019 at 7:52 AM Ira Weiny wrote: > > On Thu, May 30, 2019 at 04:21:19PM -0700, John Hubbard wrote: > > On 5/30/19 2:47 PM, Ira Weiny wrote: > > > On Thu, May 30, 2019 at 06:54:04AM +0800, Pingfan Liu wrote: > > [...] > > >> + for (j = i; j < nr; j++) > > >> + put_page(pages[j]); > > > > > > Should be put_user_page() now. For now that just calls put_page() but it is > > > slated to change soon. > > > > > > I also wonder if this would be more efficient as a check as we are walking the > > > page tables and bail early. > > > > > > Perhaps the code complexity is not worth it? > > > > Good point, it might be worth it. Because now we've got two loops that > > we run, after the interrupts-off page walk, and it's starting to look like > > a potential performance concern. > > FWIW I don't see this being a huge issue at the moment. Perhaps those more > familiar with CMA can weigh in here. How was this issue found? If it was > found by running some test perhaps that indicates a performance preference? > I found the bug by reading code. And I do not see any performance concern. Bailing out early contritute little to performance, as we fall on the slow path immediately. Regards, Pingfan [....]