From patchwork Mon Aug 26 23:32:40 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mina Almasry X-Patchwork-Id: 11115803 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id CA17B14F7 for ; Mon, 26 Aug 2019 23:33:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9CAE02053B for ; Mon, 26 Aug 2019 23:33:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="BfXwwjAu" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727926AbfHZXdT (ORCPT ); Mon, 26 Aug 2019 19:33:19 -0400 Received: from mail-qt1-f202.google.com ([209.85.160.202]:34249 "EHLO mail-qt1-f202.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727788AbfHZXdS (ORCPT ); Mon, 26 Aug 2019 19:33:18 -0400 Received: by mail-qt1-f202.google.com with SMTP id f19so8280773qtq.1 for ; Mon, 26 Aug 2019 16:33:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=5FDOwwCe+APWdEQQqNbBpE6iIki5NU5vXPefDHikBmg=; b=BfXwwjAuhrLzwyV49VnJL7NxDepEgABTklx9qhc6rCK5F1w2xw2LFgmzTWfEAHiPTF c5v46KJZa6ts7LaEAl2UEDScmWBYH5FdRRkicG6JhCd5gzMC/MBrJM+gYNO8Y0DVWbd5 NXpoHq7M83Am1Y0GWNerd7Jl1ueGsflkoKLPII48XaDmWf1gZAsG9uA8s1QmT0b9GiBR N55L5aExlS7kaRIdXdaPfI1XlO+g1o6LMycyymR5h1zGtC9eyWIzaUH81AY7A3AqGLvk we6DYp4QKXYWKwHLDCaThtFG284KWl3dBsOd8oJmCEJHfUQZs3Chk6Cz9lgq6vY8+BVj jxoQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=5FDOwwCe+APWdEQQqNbBpE6iIki5NU5vXPefDHikBmg=; b=GHZ2JJMbPTs+uXHW+ub3iDMh1fwim8UsMvRArdT9bh1Rt+h2T32m3ZEmVOJfgoyX7e uJNGpYPcJsbCfJkg9D6ebghG+IuoiuHEcGo1Uf0joQEnA+6rTqjWPpqbL5qWev21bzzM FtHOmm6Mw/4AAaPOzxxMBaEd728JzNQrEIDSLmI+EAcxF8XaenjoZ3SNJZzfORtuBQK5 RRv1eAnkN5vLHOD7sLZmrYh48IL2CPNkO/I2g+Z/lPIYV3R0jomB6jM3iQAXWSDArGRw elPVboLhA72pGd9PA4XxAc0EwG+L8YcspFI0Gksb+WY9XHzmT3rDtABXTiCgTrO+mQSH ZIcQ== X-Gm-Message-State: APjAAAXpmA5E7p4Oa1l16MigaFj3IzZ/qXEuWiqVAGZ3uu6iJvdK7F2F 3hWAJQhY2ZnzHpnEg6g8kH/NrHPwCpp67fbxgQ== X-Google-Smtp-Source: APXvYqyDImAPzfr0N58wa/tY2W7Edq/krF5d6f1tRQcHXjvREDYlfn3oZlUNIZ7WqjjdFcG1GxtewDdCNH22t72/9w== X-Received: by 2002:ad4:45d3:: with SMTP id v19mr17564793qvt.90.1566862396925; Mon, 26 Aug 2019 16:33:16 -0700 (PDT) Date: Mon, 26 Aug 2019 16:32:40 -0700 In-Reply-To: <20190826233240.11524-1-almasrymina@google.com> Message-Id: <20190826233240.11524-7-almasrymina@google.com> Mime-Version: 1.0 References: <20190826233240.11524-1-almasrymina@google.com> X-Mailer: git-send-email 2.23.0.187.g17f5b7556c-goog Subject: [PATCH v3 6/6] hugetlb_cgroup: Add hugetlb_cgroup reservation docs From: Mina Almasry To: mike.kravetz@oracle.com Cc: shuah@kernel.org, almasrymina@google.com, 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 Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Add docs for how to use hugetlb_cgroup reservations, and their behavior. --- .../admin-guide/cgroup-v1/hugetlb.rst | 84 ++++++++++++++++--- 1 file changed, 73 insertions(+), 11 deletions(-) -- 2.23.0.187.g17f5b7556c-goog 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. +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. + +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.