From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D28EFC4CECD for ; Tue, 17 Sep 2019 01:58:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9E91D20880 for ; Tue, 17 Sep 2019 01:58:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568685505; bh=bk6B2U84a5RejyELSSMB0s9gF3GyzUbvyJlOCbss36c=; h=Subject:To:Cc:References:From:Date:In-Reply-To:List-ID:From; b=1njg1M1y1bmIWo0zHxsXXaEG6lBW4jlfq6LfU6qZ9IGcLDFiZnthutpzvdsDmoii8 Mw1vD55ffzrJ1XCSbTMkZZNmgqLC3HGns5PcyNYXdgYrIWq21jcuQaOUVpmu4yJnMO PIlNNd+R+Z56wHsmupKYJSSUWoclaEVaL/qAO01Q= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391923AbfIQB6Z (ORCPT ); Mon, 16 Sep 2019 21:58:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:41738 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391791AbfIQB6Y (ORCPT ); Mon, 16 Sep 2019 21:58:24 -0400 Received: from [192.168.1.112] (c-24-9-64-241.hsd1.co.comcast.net [24.9.64.241]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 004D120678; Tue, 17 Sep 2019 01:58:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568685503; bh=bk6B2U84a5RejyELSSMB0s9gF3GyzUbvyJlOCbss36c=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=yV7h5TO0jv/mZK4weNy1RqawMfaZpiR1UnBax+wLu1dpACewB5A/hnnYXUML7rmCk Ucp07G5I7XDYoK/6tP7ubuXhbjjP1ZQY5usW6StqPMH2qanApsnyF3bbIWKLvGHyMN FEsvy7cAj3qrYb4TB4crlTa5PKn1ESzgwFovm2Kg= Subject: Re: [PATCH v4 9/9] hugetlb_cgroup: Add hugetlb_cgroup reservation docs To: Mina Almasry , mike.kravetz@oracle.com Cc: rientjes@google.com, shakeelb@google.com, gthelen@google.com, akpm@linux-foundation.org, khalid.aziz@oracle.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, cgroups@vger.kernel.org, aneesh.kumar@linux.vnet.ibm.com, mkoutny@suse.com, Hillf Danton , shuah References: <20190910233146.206080-1-almasrymina@google.com> <20190910233146.206080-10-almasrymina@google.com> From: shuah Message-ID: <9fdff535-5f36-ca91-3905-630c18858170@kernel.org> Date: Mon, 16 Sep 2019 19:58:20 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190910233146.206080-10-almasrymina@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/10/19 5:31 PM, Mina Almasry wrote: > Add docs for how to use hugetlb_cgroup reservations, and their behavior. > > Signed-off-by: Mina Almasry > Acked-by: Hillf Danton > --- > .../admin-guide/cgroup-v1/hugetlb.rst | 84 ++++++++++++++++--- > 1 file changed, 73 insertions(+), 11 deletions(-) > > diff --git a/Documentation/admin-guide/cgroup-v1/hugetlb.rst b/Documentation/admin-guide/cgroup-v1/hugetlb.rst > index a3902aa253a96..cc6eb859fc722 100644 > --- a/Documentation/admin-guide/cgroup-v1/hugetlb.rst > +++ b/Documentation/admin-guide/cgroup-v1/hugetlb.rst > @@ -2,13 +2,6 @@ > HugeTLB Controller > ================== > > -The HugeTLB controller allows to limit the HugeTLB usage per control group and > -enforces the controller limit during page fault. Since HugeTLB doesn't > -support page reclaim, enforcing the limit at page fault time implies that, > -the application will get SIGBUS signal if it tries to access HugeTLB pages > -beyond its limit. This requires the application to know beforehand how much > -HugeTLB pages it would require for its use. > - > HugeTLB controller can be created by first mounting the cgroup filesystem. > > # mount -t cgroup -o hugetlb none /sys/fs/cgroup > @@ -28,10 +21,14 @@ process (bash) into it. > > Brief summary of control files:: > > - hugetlb..limit_in_bytes # set/show limit of "hugepagesize" hugetlb usage > - hugetlb..max_usage_in_bytes # show max "hugepagesize" hugetlb usage recorded > - hugetlb..usage_in_bytes # show current usage for "hugepagesize" hugetlb > - hugetlb..failcnt # show the number of allocation failure due to HugeTLB limit > + hugetlb..reservation_limit_in_bytes # set/show limit of "hugepagesize" hugetlb reservations > + hugetlb..reservation_max_usage_in_bytes # show max "hugepagesize" hugetlb reservations recorded > + hugetlb..reservation_usage_in_bytes # show current reservations for "hugepagesize" hugetlb > + hugetlb..reservation_failcnt # show the number of allocation failure due to HugeTLB reservation limit > + hugetlb..limit_in_bytes # set/show limit of "hugepagesize" hugetlb faults > + hugetlb..max_usage_in_bytes # show max "hugepagesize" hugetlb usage recorded > + hugetlb..usage_in_bytes # show current usage for "hugepagesize" hugetlb > + hugetlb..failcnt # show the number of allocation failure due to HugeTLB usage limit > > For a system supporting three hugepage sizes (64k, 32M and 1G), the control > files include:: > @@ -40,11 +37,76 @@ files include:: > hugetlb.1GB.max_usage_in_bytes > hugetlb.1GB.usage_in_bytes > hugetlb.1GB.failcnt > + hugetlb.1GB.reservation_limit_in_bytes > + hugetlb.1GB.reservation_max_usage_in_bytes > + hugetlb.1GB.reservation_usage_in_bytes > + hugetlb.1GB.reservation_failcnt > hugetlb.64KB.limit_in_bytes > hugetlb.64KB.max_usage_in_bytes > hugetlb.64KB.usage_in_bytes > hugetlb.64KB.failcnt > + hugetlb.64KB.reservation_limit_in_bytes > + hugetlb.64KB.reservation_max_usage_in_bytes > + hugetlb.64KB.reservation_usage_in_bytes > + hugetlb.64KB.reservation_failcnt > hugetlb.32MB.limit_in_bytes > hugetlb.32MB.max_usage_in_bytes > hugetlb.32MB.usage_in_bytes > hugetlb.32MB.failcnt > + hugetlb.32MB.reservation_limit_in_bytes > + hugetlb.32MB.reservation_max_usage_in_bytes > + hugetlb.32MB.reservation_usage_in_bytes > + hugetlb.32MB.reservation_failcnt > + > + > +1. Reservation limits > + > +The HugeTLB controller allows to limit the HugeTLB reservations per control > +group and enforces the controller limit at reservation time. Reservation limits > +are superior to Page fault limits (see section 2), since Reservation limits are > +enforced at reservation time, and never causes the application to get SIGBUS > +signal. Instead, if the application is violating its limits, then it gets an > +error on reservation time, i.e. the mmap or shmget return an error. > + > + > +2. Page fault limits > + > +The HugeTLB controller allows to limit the HugeTLB usage (page fault) per > +control group and enforces the controller limit during page fault. Since HugeTLB > +doesn't support page reclaim, enforcing the limit at page fault time implies > +that, the application will get SIGBUS signal if it tries to access HugeTLB > +pages beyond its limit. This requires the application to know beforehand how > +much HugeTLB pages it would require for its use. > + > + > +3. Caveats with shared memory > + > +a. Charging and uncharging: > + > +For shared hugetlb memory, both hugetlb reservation and usage (page faults) are > +charged to the first task that causes the memory to be reserved or faulted, > +and all subsequent uses of this reserved or faulted memory is done without > +charging. > + > +Shared hugetlb memory is only uncharged when it is unreseved or deallocated. Spelling? > +This is usually when the hugetlbfs file is deleted, and not when the task that > +caused the reservation or fault has exited. > + > +b. Interaction between reservation limit and fault limit. > + > +Generally, it's not recommended to set both of the reservation limit and fault > +limit in a cgroup. For private memory, the fault usage cannot exceed the > +reservation usage, so if you set both, one of those limits will be useless. > + Is this enforced? What happens when attempt is made to set fault limit on a cgroup that has reservation limit and vice versa. > +For shared memory, a cgroup's fault usage may be greater than its reservation > +usage, so some care needs to be taken. Consider this example: > + > +- Task A reserves 4 pages in a shared hugetlbfs file. Cgroup A will get > + 4 reservations charged to it and no faults charged to it. > +- Task B reserves and faults the same 4 pages as Task A. Cgroup B will get no > + reservation charge, but will get charged 4 faulted pages. If Cgroup B's limit > + is less than 4, then Task B will get a SIGBUS. > + > +For the above scenario, it's not recommended for the userspace to set both > +reservation limits and fault limits, but it is still allowed to in case it sees > +some use for it. What would be the scenarios where setting both could be useful? Please explain. > -- > 2.23.0.162.g0b9fbb3734-goog > thanks, -- Shuah