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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 7D97EC47082 for ; Tue, 8 Jun 2021 11:55:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 683036128D for ; Tue, 8 Jun 2021 11:55:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232343AbhFHL46 (ORCPT ); Tue, 8 Jun 2021 07:56:58 -0400 Received: from mail-qt1-f174.google.com ([209.85.160.174]:45870 "EHLO mail-qt1-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232290AbhFHL4s (ORCPT ); Tue, 8 Jun 2021 07:56:48 -0400 Received: by mail-qt1-f174.google.com with SMTP id l17so10853709qtq.12; Tue, 08 Jun 2021 04:54:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=pJTwc2+8OmVO0WYs0LS9qDVADcgdZ32QIgWE+KhO6qY=; b=Ed5PIja2L89hTEZqu5p9+ymg2BMEhGDZZ1DfUAX1zG4emZcFOuPPjaUF7Rg6Oq4yZ1 Bspb2FZhAzvQMP1K6Ecmsv+Yba8KIxnjz/eW73Jgf0JL81xq5iztd86lXEBm21A+8bYf E3IGDYaBcXVJKr5jEc9fPBh9+Pr8VUkWsRDwdSeVul6n3PVOP88PX/sDRCijZ/ok6J6O /zZwsDZIBDqVwA7+pncCkr/fPE0DbEgBGcqC+tJPjhZReHvs/+QoFFeybt/8F0LNnHj/ mvjGiGd5H047N4ckB/IqIyM630FO2IFGOq+o/kU2IfpJd7lvfWNLwpdIW/jqONIEMOyN MYow== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=pJTwc2+8OmVO0WYs0LS9qDVADcgdZ32QIgWE+KhO6qY=; b=P7O4NGs89yD/7xf+WRL9F/HCPmKHYDq0qj6V0khatqETB69oh9NMg5/6ni5ODuZy5s mES+aKOMeKXB30Z/WgT77gkpldVlbhnn3b1SJOwIPBDhz8oPSuRp3d+HLT+aLvjcp8u0 LbBnGpSQy2JCHq6XrrA7BhMz/Pd1vdQ5PjxzjvvHlIQtKqGETkDgcJAp6dSTQiSCdU5S C+YNCTlosF5zYngm+7/YOPWZH9CqNVjSuifPHHDpT2MZExPU/l0ml1dxsnuzgEPBSN1g XBiI6gCwZL0BI+LjMqYxB3PIGOeZ4AAWPCBbK36XcNUo7I0+ceOgjiujAOEoeBS9vLF2 Stdg== X-Gm-Message-State: AOAM533icG7Vbg2kiwDNUNJlDfeWGQxKZ/Zcr7OOAMDDkjCufRQj5ISC cLn+QfLX61V/L0bVyAuVyZ4= X-Google-Smtp-Source: ABdhPJyqXfjoMNVb/P2WbZokEeqnYl1dmsZF5orqEbrbRbGD7efJeeKKimDTO5AEr2MfND2mDEzgTw== X-Received: by 2002:ac8:67c2:: with SMTP id r2mr6361570qtp.131.1623153222062; Tue, 08 Jun 2021 04:53:42 -0700 (PDT) Received: from localhost.localdomain (ec2-35-169-212-159.compute-1.amazonaws.com. [35.169.212.159]) by smtp.gmail.com with ESMTPSA id h4sm2133927qth.66.2021.06.08.04.53.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Jun 2021 04:53:41 -0700 (PDT) From: SeongJae Park To: akpm@linux-foundation.org Cc: SeongJae Park , Jonathan.Cameron@Huawei.com, acme@kernel.org, alexander.shishkin@linux.intel.com, amit@kernel.org, benh@kernel.crashing.org, brendanhiggins@google.com, corbet@lwn.net, david@redhat.com, dwmw@amazon.com, elver@google.com, fan.du@intel.com, foersleo@amazon.de, greg@kroah.com, gthelen@google.com, guoju.fgj@alibaba-inc.com, jgowans@amazon.com, mgorman@suse.de, minchan@kernel.org, mingo@redhat.com, namhyung@kernel.org, peterz@infradead.org, riel@surriel.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, shakeelb@google.com, shuah@kernel.org, sj38.park@gmail.com, snu@zelle79.org, vbabka@suse.cz, vdavydov.dev@gmail.com, zgf574564920@gmail.com, linux-damon@amazon.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [RFC v2 14/14] Documentation/admin-guide/mm/damon: Add a document for DAMON_RECLAIM Date: Tue, 8 Jun 2021 11:52:54 +0000 Message-Id: <20210608115254.11930-15-sj38.park@gmail.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20210608115254.11930-1-sj38.park@gmail.com> References: <20210608115254.11930-1-sj38.park@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: SeongJae Park This commit adds an admin-guide document for DAMON-based Reclamation. Signed-off-by: SeongJae Park --- Documentation/admin-guide/mm/damon/index.rst | 1 + .../admin-guide/mm/damon/reclaim.rst | 211 ++++++++++++++++++ 2 files changed, 212 insertions(+) create mode 100644 Documentation/admin-guide/mm/damon/reclaim.rst diff --git a/Documentation/admin-guide/mm/damon/index.rst b/Documentation/admin-guide/mm/damon/index.rst index 0baae7a5402b..e5b4da13f60b 100644 --- a/Documentation/admin-guide/mm/damon/index.rst +++ b/Documentation/admin-guide/mm/damon/index.rst @@ -13,3 +13,4 @@ Using this, users can analyze and optimize their systems. start guide usage + reclaim diff --git a/Documentation/admin-guide/mm/damon/reclaim.rst b/Documentation/admin-guide/mm/damon/reclaim.rst new file mode 100644 index 000000000000..b4fe0c16f72e --- /dev/null +++ b/Documentation/admin-guide/mm/damon/reclaim.rst @@ -0,0 +1,211 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================= +DAMON-based Reclamation +======================= + +DAMON-based Reclamation (DAMON_RECLAIM) is a static kernel module that aimed to +be used for proactive and lightweight reclamation under light memory pressure. +It doesn't aim to replace the LRU-list based page_granularity reclamation, but +to be selectively used for different level of memory pressure and requirements. + +Where Proactive Reclamation is Required? +======================================== + +On general memory over-committed systems, proactively reclaiming cold pages +helps saving memory and reducing latency spikes that incurred by the direct +reclaim of the process or CPU consumption of kswapd, while incurring only +minimal performance degradation [1]_ [2]_ . + +Free Pages Reporting [3]_ based memory over-commit virtualization systems are +good example of the cases. In such systems, the guest VMs reports their free +memory to host, and the host reallocates the reported memory to other guests. +As a result, the memory of the systems are fully utilized. However, the +guests could be not so memory-frugal, mainly because some kernel subsystems and +user-space applications are designed to use as much memory as available. Then, +guests could report only small amount of memory as free to host, results in +memory utilization drop of the systems. Running the proactive reclamation in +guests could mitigate this problem. + +How It Works? +============= + +DAMON_RECLAIM finds memory regions that didn't accessed for specific time +duration and page out. To avoid it consuming too much CPU for the paging out +operation, a speed limit can be configured. Under the speed limit, it pages +out memory regions that didn't accessed longer time first. System +administrators can also configure under what situation this scheme should +automatically activated and deactivated with three memory pressure watermarks. + +Interface: Module Parameters +============================ + +To use this feature, you should first ensure your system is running on a kernel +that is built with ``CONFIG_DAMON_RECLAIM=y``. + +To let sysadmins enable or disable it and tune for the given system, +DAMON_RECLAIM utilizes module parameters. That is, you can put +``damon_reclaim.=`` on the kernel boot command line or write +proper values to ``/sys/modules/damon_reclaim/parameters/`` files. + +Note that the parameter values except ``enabled`` are applied only when +DAMON_RECLAIM starts. Therefore, if you want to apply new parameter values in +runtime and DAMON_RECLAIM is already enabled, you should disable and re-enable +it via ``enabled`` parameter file. Writing of the new values to proper +parameter values should be done before the re-enablement. + +Below are the description of each parameter. + +enabled +------- + +Enable or disable DAMON_RECLAIM. + +You can enable DAMON_RCLAIM by setting the value of this parameter as ``Y``. +Setting it as ``N`` disables DAMON_RECLAIM. Note that DAMON_RECLAIM could do +no real monitoring and reclamation due to the watermarks-based activation +condition. Refer to below descriptions for the watermarks parameter for this. + +min_age +------- + +Time threshold for cold memory regions identification in microseconds. + +If a memory region is not accessed for this or longer time, DAMON_RECLAIM +identifies the region as cold, and reclaims it. + +limit_sz +-------- + +Maximum bytes of memory that can be reclaimed in a charging window. + +DAMON_RECLAIM counts amount of memory which has reclaimed within current +charging time window and avoids reclaiming more than this limit in current time +window. This could be useful for limiting CPU consumption of DAMON_RECLAIM. + +limit_ms +-------- + +The reclaimed memory charging window in milliseconds. + +wmarks_interval +--------------- + +Minimal time to wait before checking the watermarks, when DAMON_RECLAIM is +enabled but inactive due to its watermarks rule. + +wmarks_high +----------- + +Free memory rate (per thousand) for the high watermark. + +If free memory of the system in bytes per thousand bytes is higher than this, +DAMON_RECLAIM becomes inactive, so it does nothing but only periodically checks +the watermarks. + +wmarks_mid +---------- + +Free memory rate (per thousand) for the middle watermark. + +If free memory of the system in bytes per thousand bytes is between this and +the low watermark, DAMON_RECLAIM becomes active, so starts the monitoring and +the reclaiming. + +wmarks_low +---------- + +Free memory rate (per thousand) for the low watermark. + +If free memory of the system in bytes per thousand bytes is lower than this, +DAMON_RECLAIM becomes inactive, so it does nothing but periodically checks the +watermarks. In the case, the system falls back to the LRU-list based page +granularity reclamation logic. + +sample_interval +--------------- + +Sampling interval for the monitoring in microseconds. + +The sampling interval of DAMON for the cold memory monitoring. Please refer to +the DAMON documentation (:doc:`usage`) for more detail. + +aggr_interval +------------- + +Aggregation interval for the monitoring in microseconds. + +The aggregation interval of DAMON for the cold memory monitoring. Please +refer to the DAMON documentation (:doc:`usage`) for more detail. + +min_nr_regions +-------------- + +Minimum number of monitoring regions. + +The minimal number of monitoring regions of DAMON for the cold memory +monitoring. This can be used to set lower-bound of the monitoring quality. +But, setting this too high could result in increased monitoring overhead. +Please refer to the DAMON documentation (:doc:`usage`) for more detail. + +max_nr_regions +-------------- + +Maximum number of monitoring regions. + +The maximum number of monitoring regions of DAMON for the cold memory +monitoring. This can be used to set upper-bound of the monitoring overhead. +However, setting this too low could result in bad monitoring quality. Please +refer to the DAMON documentation (:doc:`usage`) for more detail. + +monitor_region_start +-------------------- + +Start of target memory region in physical address. + +The start physical address of memory region that DAMON_RECLAIM will do work +against. That is, DAMON_RECLAIM will find cold memory regions in this region +and reclaims. By default, biggest System RAM is used as the region. + +monitor_region_end +------------------ + +End of target memory region in physical address. + +The end physical address of memory region that DAMON_RECLAIM will do work +against. That is, DAMON_RECLAIM will find cold memory regions in this region +and reclaims. By default, biggest System RAM is used as the region. + +kdamond_pid +----------- + +PID of the DAMON thread. + +If DAMON_RECLAIM is enabled, this becomes the PID of the worker thread. Else, +-1. + +Example +======= + +Below runtime example commands make DAMON_RECLAIM to find memory regions that +not accessed for 30 seconds or more and pages out. The reclamation is limited +to be done only up to 1 GiB per second to avoid DAMON_RECLAIM consuming too +much CPU time for the paging out operation. It also asks DAMON_RECLAIM to do +nothing if the system's free memory rate is more than 50%, but start the real +works if it becomes lower than 40%. If DAMON_RECLAIM doesn't make progress and +therefore the free memory rate becomes lower than 20%, it asks DAMON_RECLAIM to +do nothing again, so that we can fall back to the LRU-list based page +granularity reclamation. :: + + # cd /sys/modules/damon_reclaim/parameters + # echo 30000000 > min_age + # echo $((1 * 1024 * 1024 * 1024)) > limit_sz + # echo 1000 > limit_ms + # echo 500 > wmarks_high + # echo 400 > wmarks_mid + # echo 200 > wmarks_low + # echo Y > enabled + +.. [1] https://research.google/pubs/pub48551/ +.. [2] https://lwn.net/Articles/787611/ +.. [3] https://www.kernel.org/doc/html/latest/vm/free_page_reporting.html -- 2.17.1