From patchwork Tue Oct 19 15:07:31 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 12570305 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B6077C433EF for ; Tue, 19 Oct 2021 15:08:29 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6C42C61260 for ; Tue, 19 Oct 2021 15:08:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 6C42C61260 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 61F796B009A; Tue, 19 Oct 2021 11:08:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 583456B009C; Tue, 19 Oct 2021 11:08:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 453FA6B009A; Tue, 19 Oct 2021 11:08:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0020.hostedemail.com [216.40.44.20]) by kanga.kvack.org (Postfix) with ESMTP id 2E0E96B009A for ; Tue, 19 Oct 2021 11:08:17 -0400 (EDT) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id E032082499A8 for ; Tue, 19 Oct 2021 15:08:16 +0000 (UTC) X-FDA: 78713517792.16.7CF2768 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf18.hostedemail.com (Postfix) with ESMTP id 80271400208D for ; Tue, 19 Oct 2021 15:08:13 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 372A16103D; Tue, 19 Oct 2021 15:08:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1634656095; bh=J4QyScO9a2R/URvbInxHpXWm3yyWpIQ3XVXMTk2ebPs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=L/nfYTByTW2otHwU5mfkT5Y8VkSMM37jUK9d28/uDwcF+nyxy6WwEDtg4ErEtK79I oidZ0630uffBCtiYnTjFauIS/NYWH7F/gJcTlEhajTLb8IN/zYdtCniXYnhx/iO3BC tmH3/cbpL32vMC3fE8Hv0Kc5EFtgUyt4rYrPtHR4xvoJc2beqwgot65z5h8ib2+JbS UMr/XrgwRsjSvmUi3pUZqjgN6NpjW8ah3A8sVFGHP4xpW0ybUwHPBx8xgCIa+njIh+ cz32BjpwEf66VdawtRyWUYKM2SPE5g3A7xbK4gCAYyRelS3LBn2BMUwjkzvdEGMhbP IHjFxQGU7jvNQ== From: SeongJae Park To: akpm@linux-foundation.org Cc: SeongJae Park , Jonathan.Cameron@Huawei.com, amit@kernel.org, benh@kernel.crashing.org, corbet@lwn.net, david@redhat.com, dwmw@amazon.com, elver@google.com, foersleo@amazon.de, gthelen@google.com, markubo@amazon.de, rientjes@google.com, shakeelb@google.com, shuah@kernel.org, linux-damon@amazon.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 15/15] Documentation/admin-guide/mm/damon: Add a document for DAMON_RECLAIM Date: Tue, 19 Oct 2021 15:07:31 +0000 Message-Id: <20211019150731.16699-16-sj@kernel.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20211019150731.16699-1-sj@kernel.org> References: <20211019150731.16699-1-sj@kernel.org> X-Rspamd-Queue-Id: 80271400208D X-Stat-Signature: rryqx1icmirgupymyc4dxrwn9hkuygmg Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="L/nfYTBy"; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf18.hostedemail.com: domain of sj@kernel.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=sj@kernel.org X-Rspamd-Server: rspam02 X-HE-Tag: 1634656093-842729 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: 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 | 235 ++++++++++++++++++ 2 files changed, 236 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 8c5dde3a5754..61aff88347f3 100644 --- a/Documentation/admin-guide/mm/damon/index.rst +++ b/Documentation/admin-guide/mm/damon/index.rst @@ -13,3 +13,4 @@ optimize those. start 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..fb9def3a7355 --- /dev/null +++ b/Documentation/admin-guide/mm/damon/reclaim.rst @@ -0,0 +1,235 @@ +.. 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. + +120 seconds by default. + +quota_ms +-------- + +Limit of time for the reclamation in milliseconds. + +DAMON_RECLAIM tries to use only up to this time within a time window +(quota_reset_interval_ms) for trying reclamation of cold pages. This can be +used for limiting CPU consumption of DAMON_RECLAIM. If the value is zero, the +limit is disabled. + +10 ms by default. + +quota_sz +-------- + +Limit of size of memory for the reclamation in bytes. + +DAMON_RECLAIM charges amount of memory which it tried to reclaim within a time +window (quota_reset_interval_ms) and makes no more than this limit is tried. +This can be used for limiting consumption of CPU and IO. If this value is +zero, the limit is disabled. + +128 MiB by default. + +quota_reset_interval_ms +----------------------- + +The time/size quota charge reset interval in milliseconds. + +The charget reset interval for the quota of time (quota_ms) and size +(quota_sz). That is, DAMON_RECLAIM does not try reclamation for more than +quota_ms milliseconds or quota_sz bytes within quota_reset_interval_ms +milliseconds. + +1 second by default. + +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)) > quota_sz + # echo 1000 > quota_reset_interval_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