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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 370BCC44536 for ; Wed, 22 Jul 2026 22:54:08 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3AE1A6B00C3; Wed, 22 Jul 2026 18:54:07 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 35EF96B00C4; Wed, 22 Jul 2026 18:54:07 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 277C46B00C5; Wed, 22 Jul 2026 18:54:07 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id F2C066B00C3 for ; Wed, 22 Jul 2026 18:54:06 -0400 (EDT) Received: from smtpin09.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 8044214032C for ; Wed, 22 Jul 2026 22:54:06 +0000 (UTC) X-FDA: 85017917292.09.19BD2E8 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf12.hostedemail.com (Postfix) with ESMTP id 4E06540003 for ; Wed, 22 Jul 2026 22:54:04 +0000 (UTC) Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=0+cFNP5V; spf=pass (imf12.hostedemail.com: domain of akpm@linux-foundation.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1784760844; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=ZZH0UCJW2OUCFvq2mZvsq/vH6LEHSHRw0NfCnh2a/1c=; b=DkjHwzXLter9dtC+34uU8EAruYRQxXh9K2sKGoIWwaqKYaDhvp/7QDKIYyiODnqllUySRq eGoVf0EzseZ0CA9ZKOdBbHacAhGJ8JqivyYaKdT1/nuwY9OU7VTATdryUCXDrJGMUm31+e SzJKXBwMhKZE3lTegJSIhPoCjlxMbp4= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1784760844; b=62R0g8yt7Qgu7se9nOFOlDbMeYxW2co11V/wbXc3vO2TFHPEi5uEno7+e0opuZ+dElk5Om Z9HkFl+v7bROCTCGj1wI31OTfqL2zJtz0U+OEb8D9fqHtVGEySzcvJtaQ5zuuy+sKEC+qW vovauVU3deUmPae56XBvHXmMCfWp/qo= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=0+cFNP5V; spf=pass (imf12.hostedemail.com: domain of akpm@linux-foundation.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 8AA31600AB; Wed, 22 Jul 2026 22:54:03 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E42431F000E9; Wed, 22 Jul 2026 22:54:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1784760843; bh=ZZH0UCJW2OUCFvq2mZvsq/vH6LEHSHRw0NfCnh2a/1c=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=0+cFNP5VCjlcHpDbvEpfxcNnlP3pj6eAQgM+HLiNXa+SMAGtEo5bRYzNZS+dsUwUy 1hTF41aqNo2etfxJz3CBoyRGO1uyg8rQ5p3k9ozOGm/t2ct6lEVcxf3InCdxoT1kvR vZsrxWbd+qHtRph7/Wt70Lxwo7znJ/n89iyKB1+U= Date: Wed, 22 Jul 2026 15:54:02 -0700 From: Andrew Morton To: pratmal@google.com Cc: Anshuman Khandual , David Hildenbrand , Vlastimil Babka , Greg Thelen , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm/page_reporting: Add page_reporting_delay_ms sysctl Message-Id: <20260722155402.f313e8a98615bd3b513221eb@linux-foundation.org> In-Reply-To: <20260722211517.1898228-1-pratmal@google.com> References: <20260722211517.1898228-1-pratmal@google.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: mrg5q3z7e8kosetgix8xnzfb1hhredc7 X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 4E06540003 X-HE-Tag: 1784760844-801479 X-HE-Meta: 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 8uLwm4hK 14XbP8bwcPzCdF314sJBEDGx9VTSSenMio4BinTCVAdKEDmwcwWveoYx5+q5nh3Ddb2G/gCMsA8a3fWNU/563x2QPLOjW/XLygXbpZzF/Eo8BNzL/FokgvIdvYPnrHBtzrnmOTSdRaQLd4DWFcOn6HOsQz3fesj4oe3BFv1jRKksTY7v7LLI48ysAXS2qyVsoffmVSpu1MpIuaNimNCHaNU1tX6rZQHCSwyMqW3V3eZiUTNE4bGCT3Gw2Wsmk574PyKSpd9foERluFSUWVuiCfs8JIP8yxPrXL7iaue+NurM2C6UTaTUzBF01bopaiwUzpRwM Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 22 Jul 2026 21:15:17 +0000 pratmal@google.com wrote: > From: Pratyush Mallick > > Currently, the free page reporting daemon uses a hardcoded delay of > (2 HZ) between reporting intervals. While this is a reasonable > default, it lacks the flexibility to adapt to varying guest workloads. > > A low delay allows aggressive memory reclamation, returning unused > pages to the host as quickly as possible. However, during spiky > allocation/free churn, this immediate reporting can lead to a severe > performance penalty (nested page faults) as the guest re-allocates memory > that the host has just unmapped. In these scenarios, there is benefit > from increasing the delay to batch free pages over a longer window, > absorbing the churn without hypercall and re-fault overhead. > > This patch refactors the delay into a dynamically tunable sysctl, > /proc/sys/vm/page_reporting_delay_ms, measured in milliseconds. The value > defaults to 2000ms to precisely match the original (2 HZ) behavior. > Seems reasonable. > +The default value is 2000 (2 seconds). The minimum allowed value is > +0 (immediate reporting) and the maximum allowed value is 10000 (10 seconds). Why implement a max? If setting it to something enormous causes bad behavior then Don't Do That?