From patchwork Tue Feb 11 21:31:28 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mina Almasry X-Patchwork-Id: 11376943 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 ECD6B1820 for ; Tue, 11 Feb 2020 21:32:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CC2DF20873 for ; Tue, 11 Feb 2020 21:32:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="AW3+a6Hp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727855AbgBKVcI (ORCPT ); Tue, 11 Feb 2020 16:32:08 -0500 Received: from mail-pj1-f74.google.com ([209.85.216.74]:54748 "EHLO mail-pj1-f74.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727856AbgBKVcG (ORCPT ); Tue, 11 Feb 2020 16:32:06 -0500 Received: by mail-pj1-f74.google.com with SMTP id a31so2318920pje.4 for ; Tue, 11 Feb 2020 13:32:06 -0800 (PST) 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=vqDD6Gs7ngqLSWc3KTUHIOcGSlcLabi4lsGh3QCG31M=; b=AW3+a6HpfbMIZUeziVe7326NVlNXRe6KKs/Jy9Bv8LgX23ZEmjRGxE1TOSLx5zOLGd BStdGUu6ZAK+vjPmmeQgLrLCE8aZNR2rMSWNwhwdr5rFsnOjag/nmx+wEftHYHwaqwQD uXhiUe/ZBtNo9TfsWaykRXTr0r/C8//JshbuuaHo1/nr7oFrZyn6VskYeG+8muDz8UWe pVBtP0+7C8imVM8fJiV1R+aH8xRUUm4VNkoBB0P78V3sSpdAHBXYuPeTrgNuSAr/htFh wVDP5VM/1gmKrcBnQ559/C3apZyOuBlSJyJBljyoPDEsdxiIu+eUll01s9kuOape4yWl XH8Q== 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=vqDD6Gs7ngqLSWc3KTUHIOcGSlcLabi4lsGh3QCG31M=; b=sXrxKK0N5KEIfU8tTeu8xXeXaV138aEj3ZCnTQ2IPbYmENenuqQTXCyttx2qXaZn1U x28k7XhMCp7wb2DdwCzDoM8FZ93Rd0tG3oiinTF3j9VdoPV6YcaJ3nZ5t5PFCYezp1+W Ahslu9ovakAiAvoIBOZUhRp5zZ+H8mixds6kr08Eh7j+ezITmqfnQl6g6KHxoZuqV+08 pnoJiVmnnz/3liwR0Ax7duokyl8lskYqWxawasZCc27kaMXY5+ZBSSbEIU9CHkuuHFYY rCOscx0sWuKWSoXExzlmEEJ8WAowPgWSxW5XXPwOitMWd4Dld7UbIXirgwjLpJStuGzc Yaeg== X-Gm-Message-State: APjAAAWKRG3EdgpdQPY8TwgFsx+QzIr+Vi5IR4Ukhk+plPL95wT22Klt PILqN01A5zbjtiJ/enaQjL+zpmtZ6yOQIuyd4A== X-Google-Smtp-Source: APXvYqzQHWOyvxutWwSWozD1YwqfvrNdtFLk+uHTrMAzzyDXIUBRUgauYZSzihOXYE/q8NSPm50+Tb4mcBrAeZ2aHg== X-Received: by 2002:a63:348c:: with SMTP id b134mr8572145pga.197.1581456726045; Tue, 11 Feb 2020 13:32:06 -0800 (PST) Date: Tue, 11 Feb 2020 13:31:28 -0800 In-Reply-To: <20200211213128.73302-1-almasrymina@google.com> Message-Id: <20200211213128.73302-9-almasrymina@google.com> Mime-Version: 1.0 References: <20200211213128.73302-1-almasrymina@google.com> X-Mailer: git-send-email 2.25.0.225.g125e21ebc7-goog Subject: [PATCH v12 9/9] 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, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, cgroups@vger.kernel.org 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. Signed-off-by: Mina Almasry Acked-by: Mike Kravetz --- Changes in v11: - Changed resv.* to rsvd.* Changes in v10: - Clarify reparenting behavior. - Reword benefits of reservation limits. Changes in v6: - Updated docs to reflect the new design based on a new counter that tracks both reservations and faults. --- .../admin-guide/cgroup-v1/hugetlb.rst | 103 ++++++++++++++++-- 1 file changed, 92 insertions(+), 11 deletions(-) -- 2.25.0.225.g125e21ebc7-goog diff --git a/Documentation/admin-guide/cgroup-v1/hugetlb.rst b/Documentation/admin-guide/cgroup-v1/hugetlb.rst index a3902aa253a96..338f2c7d7a1cd 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..rsvd.limit_in_bytes # set/show limit of "hugepagesize" hugetlb reservations + hugetlb..rsvd.max_usage_in_bytes # show max "hugepagesize" hugetlb reservations and no-reserve faults + hugetlb..rsvd.usage_in_bytes # show current reservations and no-reserve faults for "hugepagesize" hugetlb + hugetlb..rsvd.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 +37,95 @@ files include:: hugetlb.1GB.max_usage_in_bytes hugetlb.1GB.usage_in_bytes hugetlb.1GB.failcnt + hugetlb.1GB.rsvd.limit_in_bytes + hugetlb.1GB.rsvd.max_usage_in_bytes + hugetlb.1GB.rsvd.usage_in_bytes + hugetlb.1GB.rsvd.failcnt hugetlb.64KB.limit_in_bytes hugetlb.64KB.max_usage_in_bytes hugetlb.64KB.usage_in_bytes hugetlb.64KB.failcnt + hugetlb.64KB.rsvd.limit_in_bytes + hugetlb.64KB.rsvd.max_usage_in_bytes + hugetlb.64KB.rsvd.usage_in_bytes + hugetlb.64KB.rsvd.failcnt hugetlb.32MB.limit_in_bytes hugetlb.32MB.max_usage_in_bytes hugetlb.32MB.usage_in_bytes hugetlb.32MB.failcnt + hugetlb.32MB.rsvd.limit_in_bytes + hugetlb.32MB.rsvd.max_usage_in_bytes + hugetlb.32MB.rsvd.usage_in_bytes + hugetlb.32MB.rsvd.failcnt + + +1. Page fault accounting + +hugetlb..limit_in_bytes +hugetlb..max_usage_in_bytes +hugetlb..usage_in_bytes +hugetlb..failcnt + +The HugeTLB controller allows users to limit the HugeTLB usage (page fault) per +control group and enforces the 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 fault in HugeTLB +pages beyond its limit. Therefore the application needs to know exactly how many +HugeTLB pages it uses before hand, and the sysadmin needs to make sure that +there are enough available on the machine for all the users to avoid processes +getting SIGBUS. + + +2. Reservation accounting + +hugetlb..rsvd.limit_in_bytes +hugetlb..rsvd.max_usage_in_bytes +hugetlb..rsvd.usage_in_bytes +hugetlb..rsvd.failcnt + +The HugeTLB controller allows to limit the HugeTLB reservations per control +group and enforces the controller limit at reservation time and at the fault of +HugeTLB memory for which no reservation exists. Since reservation limits are +enforced at reservation time (on mmap or shget), reservation limits never causes +the application to get SIGBUS signal if the memory was reserved before hand. For +MAP_NORESERVE allocations, the reservation limit behaves the same as the fault +limit, enforcing memory usage at fault time and causing the application to +receive a SIGBUS if it's crossing its limit. + +Reservation limits are superior to page fault limits described above, since +reservation limits are enforced at reservation time (on mmap or shget), and +never causes the application to get SIGBUS signal if the memory was reserved +before hand. This allows for easier fallback to alternatives such as +non-HugeTLB memory for example. In the case of page fault accounting, it's very +hard to avoid processes getting SIGBUS since the sysadmin needs precisely know +the HugeTLB usage of all the tasks in the system and make sure there is enough +pages to satisfy all requests. Avoiding tasks getting SIGBUS on overcommited +systems is practically impossible with page fault accounting. + + +3. Caveats with shared memory + +For shared HugeTLB memory, both HugeTLB reservation and 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 unreserved or deallocated. +This is usually when the HugeTLB file is deleted, and not when the task that +caused the reservation or fault has exited. + + +4. Caveats with HugeTLB cgroup offline. + +When a HugeTLB cgroup goes offline with some reservations or faults still +charged to it, the behavior is as follows: + +- The fault charges are charged to the parent HugeTLB cgroup (reparented), +- the reservation charges remain on the offline HugeTLB cgroup. + +This means that if a HugeTLB cgroup gets offlined while there is still HugeTLB +reservations charged to it, that cgroup persists as a zombie until all HugeTLB +reservations are uncharged. HugeTLB reservations behave in this manner to match +the memory controller whose cgroups also persist as zombie until all charged +memory is uncharged. Also, the tracking of HugeTLB reservations is a bit more +complex compared to the tracking of HugeTLB faults, so it is significantly +harder to reparent reservations at offline time.