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[209.85.220.65]) by mx.google.com with SMTPS id n11sor3866907ioc.126.2019.02.06.16.27.49 for (Google Transport Security); Wed, 06 Feb 2019 16:27:49 -0800 (PST) Received-SPF: pass (google.com: domain of alexander.duyck@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=qcVNBNfz; spf=pass (google.com: domain of alexander.duyck@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=alexander.duyck@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=QjmxfddQuTfnUk2Jf9d94uGA03f2Ji4tV+lPx6DhrcU=; b=qcVNBNfzzoJH0+ab83ciTUxscvQptzm2bXho4/JSv+R7y4fY0GS7aOhx1OzaBRgXRz OTSgH6jquOw3sXi7lnso4XQOXACb7ifqnPcI9cz6+41PQyBRIVWLp9uSl2uVWn8mjf6E lhCQMe2Xe6LubrCv79nWnF6OiyL2wHi1ZeRSPkTDfbLXOXzdTvFXxFLODOmwXMMzDZIl uqyW/c0jUVR2Mtfme1RPUbm+aX+fz65Yx40t4MEj/eZq+p+M/ZqKYclAy9wNYzz+C0iV NeQhXfhog91yOksshxUK8ux53laiMA+U0+4x9C2PNqKskoFYeWI1XPcExREmyrVgoMVQ rsMA== X-Google-Smtp-Source: AHgI3IaeNTEkecukVcsQkUXZ1P+6ZkWqh2UWOKyZYicc+FHZha7sf+tg8hCR2dnCfM3UZu3Mibirrday1lovm+NSCww= X-Received: by 2002:a5e:8f0b:: with SMTP id c11mr1058613iok.116.1549499268955; Wed, 06 Feb 2019 16:27:48 -0800 (PST) MIME-Version: 1.0 References: <631c44cc-df2d-40d4-a537-d24864df0679@nvidia.com> In-Reply-To: <631c44cc-df2d-40d4-a537-d24864df0679@nvidia.com> From: Alexander Duyck Date: Wed, 6 Feb 2019 16:27:37 -0800 Message-ID: Subject: Re: No system call to determine MAX_NUMNODES? To: Ralph Campbell Cc: Linux MM , longman@redhat.com 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 Wed, Feb 6, 2019 at 3:13 PM Ralph Campbell wrote: > > I was using the latest git://git.cmpxchg.org/linux-mmotm.git and noticed > a new issue compared to 5.0.0-rc5. > > It looks like there is no convenient way to query the kernel's value for > MAX_NUMNODES yet this is used in kernel_get_mempolicy() to validate the > 'maxnode' parameter to the GET_MEMPOLICY(2) system call. > Otherwise, EINVAL is returned. > > Searching the internet for get_mempolicy yields some references that > recommend reading /proc//status and parsing the line "Mems_allowed:". > > Running "cat /proc/self/status | grep Mems_allowed:" I get: > With 5.0.0-rc5: > Mems_allowed: 00000000,00000001 > With 5.0.0-rc5-mm1: > Mems_allowed: 1 > (both kernels were config'ed with CONFIG_NODES_SHIFT=6) > > Clearly, there should be a better way to query MAX_NUMNODES like > sysconf(), sysctl(), or libnuma. Really we shouldn't need to know that. That just tells us about how the kernel was built, it doesn't really provide any information about the layout of the system. > I searched for the patch that changed /proc/self/status but didn't find it. The patch you are looking for is located at: http://lkml.kernel.org/r/1545405631-6808-1-git-send-email-longman@redhat.com I wonder if we shouldn't look at modifying kernel_get_mempolicy and the compat call to test for nr_node_ids instead of MAX_NUMNODES since the rest of the data would be useless anyway.