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b=ifDOQ1SYRWQ+Jyaxb2r8QDbxDjNXQ5IKB+Fl0NDIzg6uuMdiSx7JFI8ove6rmqEOL YnQQy3r/XW2OW+0bvyW+2jRbNH8lxFMROAZyEwnq4m9iSRiPkflC+4kPOHdbQQzFiA 4ojzOu7w0B5zjxYeiuKNF3pIA2ojGzQtSLbS7nc0= Date: Fri, 31 Jul 2026 14:34:20 -0700 From: Andrew Morton To: pratmal@google.com Cc: vbabka@kernel.org, david@kernel.org, sj@kernel.org, corbet@lwn.net, ljs@kernel.org, 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: <20260731143420.0787387ce2ca120ecee15338@linux-foundation.org> In-Reply-To: <20260731193705.2902728-1-pratmal@google.com> References: <20260731193705.2902728-1-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-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 19ABD40008 X-Rspam-User: X-Stat-Signature: ug6b5z5ipwe8az3sa3wgq13e99uso4to X-HE-Tag: 1785533662-69369 X-HE-Meta: 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 rFhgYqpo SOfE4XDxwj5ovG43xl1denKz3GCEPTzlESCm1XWShIcTD0JE9HLxPodEJyK/Vg66GVWsHJAiOBiO7f9Y0V3b35NWJhr2tYpUFtlHm5mFu+l2VA1nJsYQI0uK8E5EuyYYDVwvuZkrf03uVxeFa6/+kLAHAshvr1jygjDB1vKWRlIUS6icnjRF/HZvw57osKCnIpHqt6DFTZpGdZdJARPNxcXUHfrOHc1KyqFWO1D1TXAkc1mA50frivNUSEsoOqWsy7UeZwNIsZYj9hbJAsedyl7CylotAWAJANSzkhOExhuIweQ5U/mWuieCAsCOq4fDiWUkUEbcDnDfiT7IJsZZI08VDrg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 31 Jul 2026 19:37:05 +0000 pratmal@google.com wrote: > 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. This conflcits with the just-upstreamed 0b45f6927a1 ("mm/page_reporting: use system_freezable_wq to fix UAF during suspend") (https://lore.kernel.org/20260721005603.1710551-1-linkl@google.com). Please review my resolution: --- a/mm/page_reporting.c~mm-page_reporting-add-page_reporting_delay_ms-module-parameter +++ a/mm/page_reporting.c @@ -48,7 +48,11 @@ MODULE_PARM_DESC(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 { @@ -57,6 +61,13 @@ enum { PAGE_REPORTING_ACTIVE }; +/* schedule work for page reporting */ +static void page_reporting_schedule_work(struct page_reporting_dev_info *prdev) +{ + queue_delayed_work(system_freezable_wq, &prdev->work, + msecs_to_jiffies(page_reporting_delay_ms)); +} + /* request page reporting */ static void __page_reporting_request(struct page_reporting_dev_info *prdev) @@ -77,12 +88,10 @@ __page_reporting_request(struct page_rep 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. */ - queue_delayed_work(system_freezable_wq, &prdev->work, - PAGE_REPORTING_DELAY); + page_reporting_schedule_work(prdev); } /* notify prdev of free page reporting request */ @@ -337,13 +346,12 @@ static void page_reporting_process(struc 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) - queue_delayed_work(system_freezable_wq, &prdev->work, - PAGE_REPORTING_DELAY); + page_reporting_schedule_work(prdev); } static DEFINE_MUTEX(page_reporting_mutex); _