From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 921CA37996C; Sat, 1 Aug 2026 09:25:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785576341; cv=none; b=M0yXSu1+rG0Nj0jsQln1jGgd4+HJb4kUlxqmKL6aUTG36Vi8/mHsKuW7PetUJlfpx6y/f+OqX0bct495zqAK9lV6cK8MjYyRQOo/ElvFnDMFnCFK+YAlmkQX/5gy+bCaXFUOao4zGlblOnO262oQ7AdtuX1tAq2YfG+5KGptEdY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785576341; c=relaxed/simple; bh=M9XmZH4M5iP8qjbpSi9jwOlKI/kgMsZc0Bl4SJCkKf8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=S5bM91spav/tbbDyiAK4qo+kXzoHYH/9oWBr9ueR4U0Dv24W5W25i8izrfgn11aG6iiqoX9sCu/CGkaEnHmXRnbP9dgZXrehKoyOt9FBrz0bI5/bMd9ItlKPr/lJ8PQr0D2Pc9jvy3jVPgiYm8nWTw4DwSyp8NsXPO4XYby1P9c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MWOrIDhk; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MWOrIDhk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1CC0F1F00AC4; Sat, 1 Aug 2026 09:25:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785576340; bh=dnH8kMzvuedz5XR8h84XFqr31pF3AJSMqise3dLXv94=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=MWOrIDhk7NpRd710mAh9X31XwxvhTvYZO67pcOs5p4384DYr18f6yJ2dMsHnrL7U6 oqr2JLYspbFKTp695RDOwABAwGtkT4W46Whhzc/EyvIHxZO6jOcpVJ6dVlbkcSMETp qLyeaMZKLdl2h2zUzXedcxjFCIftmYVifVM4K2D47iVGgZ6jiU6jYOq/XVDbMCUHq4 4MGJnAYhvegUBckzxfHOdHXMrF1L/T7Bfynw0dyBPMeoz2KkRIeTeNRUSrtfBosWA6 EHRowDuVeHERq7mfdVmgrziTxmd8C/AulssOsb5KYw0dI/TmxZ50cIU6X54tEUJvrw a5dr/5n+1waEA== Date: Sat, 1 Aug 2026 10:25:20 +0100 From: "Lorenzo Stoakes (ARM)" To: pratmal@google.com Cc: akpm@linux-foundation.org, vbabka@kernel.org, david@kernel.org, sj@kernel.org, corbet@lwn.net, skhan@linuxfoundation.org, anshuman.khandual@arm.com, gthelen@google.com, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, liam@infradead.org, rppt@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCH v4] mm/page_reporting: Add page_reporting_delay_ms module parameter Message-ID: References: <20260731193705.2902728-1-pratmal@google.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260731193705.2902728-1-pratmal@google.com> On Fri, Jul 31, 2026 at 07:37:05PM +0000, pratmal@google.com wrote: > From: Pratyush Mallick > > Free page reporting currently hardcodes a 2-second interval between > reports. This rigid delay cannot accommodate diverse guest workloads. > > This patch introduces a module parameter, page_reporting_delay_ms > (default: 2000), allowing users to tune the reporting rate: > - Lower values enable aggressive memory reclamation by returning unused > pages to the host immediately. > - Higher values help batch pages during spiky allocation/free churn, > reducing hypercalls and nested page fault overheads. > > Setting the delay to 0 is safe and execution is strictly gated by: > - reporting is only triggered by high-order page frees. > - expensive hypercalls are bounded by a slot capacity watermark check > before proceeding. Thanks! > > Signed-off-by: Pratyush Mallick LGTM so: Acked-by: Lorenzo Stoakes (ARM) > --- > v4: > - Added a helper function for schedule_delayed_work(). > - Updated the commit message. > - v3: https://lore.kernel.org/linux-mm/amiPTPKfTOEpgetH@lucifer/T/#t > v3: > - Converted page_reporting_delay_ms from a sysctl to a module parameter. > - Dropped the max value cap (PAGE_REPORTING_DELAY_MS_MAX). > - Documented page_reporting.page_reporting_delay_ms in Documentation/admin-guide/kernel-parameters.txt. > - Updated code comments in mm/page_reporting.c to reflect dynamic parameterization. > - v2: https://lore.kernel.org/linux-mm/3da27fde-25dc-4cb8-8e05-74cd26fc2f7c@kernel.org/T/#t > v2: > - Documented page_reporting_delay_ms in Documentation/admin-guide/sysctl/vm.rst. > - v1: https://lore.kernel.org/linux-mm/20260722192935.1646848-1-pratmal@google.com/T/#u > v1: Fixed feedback from RFC. > - Added lower and upper cap to sysctl value. > - Reverted the reordering on page_reporting_delay_ms. > - Dropped the mod_delayed_work() change. > - RFC: https://lore.kernel.org/linux-mm/20260714171456.2350037-1-pratmal@google.com/T/#u > .../admin-guide/kernel-parameters.txt | 6 +++++ > mm/page_reporting.c | 26 +++++++++++++------ > 2 files changed, 24 insertions(+), 8 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index b5493a7f8f22..364c2dce8e70 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -4810,6 +4810,12 @@ Kernel parameters > Adjust the minimal page reporting order. The page > reporting is disabled when it exceeds MAX_PAGE_ORDER. > > + page_reporting.page_reporting_delay_ms= > + [KNL] Free page reporting delay in milliseconds > + Format: > + Adjust the delay in milliseconds between free page > + reporting intervals. Default is 2000 (2 seconds). > + > panic= [KNL] Kernel behaviour on panic: delay > timeout > 0: seconds before rebooting > timeout = 0: wait forever > diff --git a/mm/page_reporting.c b/mm/page_reporting.c > index 942e84b6908a..c01aa3af80f3 100644 > --- a/mm/page_reporting.c > +++ b/mm/page_reporting.c > @@ -47,7 +47,11 @@ MODULE_PARM_DESC(page_reporting_order, "Set page reporting order"); > */ > EXPORT_SYMBOL_GPL(page_reporting_order); > > -#define PAGE_REPORTING_DELAY (2 * HZ) > +static unsigned int page_reporting_delay_ms = 2 * MSEC_PER_SEC; > +module_param(page_reporting_delay_ms, uint, 0644); > +MODULE_PARM_DESC(page_reporting_delay_ms, > + "Set page reporting delay in milliseconds"); > + > static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly; > > enum { > @@ -56,6 +60,13 @@ enum { > PAGE_REPORTING_ACTIVE > }; > > +/* schedule work for page reporting */ > +static void page_reporting_schedule_work(struct page_reporting_dev_info *prdev) > +{ > + schedule_delayed_work(&prdev->work, > + msecs_to_jiffies(page_reporting_delay_ms)); > +} > + > /* request page reporting */ > static void > __page_reporting_request(struct page_reporting_dev_info *prdev) > @@ -76,11 +87,10 @@ __page_reporting_request(struct page_reporting_dev_info *prdev) > return; > > /* > - * Delay the start of work to allow a sizable queue to build. For > - * now we are limiting this to running no more than once every > - * couple of seconds. > + * Delay the start of work to allow a sizable queue to build. > + * We limit this based on page_reporting_delay_ms. > */ > - schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY); > + page_reporting_schedule_work(prdev); > } > > /* notify prdev of free page reporting request */ > @@ -335,12 +345,12 @@ static void page_reporting_process(struct work_struct *work) > err_out: > /* > * If the state has reverted back to requested then there may be > - * additional pages to be processed. We will defer for 2s to allow > - * more pages to accumulate. > + * additional pages to be processed. We will defer by > + * page_reporting_delay_ms to allow more pages to accumulate. > */ > state = atomic_cmpxchg(&prdev->state, state, PAGE_REPORTING_IDLE); > if (state == PAGE_REPORTING_REQUESTED) > - schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY); > + page_reporting_schedule_work(prdev); > } > > static DEFINE_MUTEX(page_reporting_mutex); > -- > 2.55.0.508.g3f0d502094-goog > -- Cheers, Lorenzo