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b=JjGo0+ef6V7aGBLPT5F6flIjmLAIVBu7nXTqOXTO5IewpJ5zjLsOqQ/jeDmpRppDP Ck1UcyOGvG5OFSJ0FyGlNR/jiDcssR0+7uWYI1i+j0CU4dtCu0z/ZOwtsLuhShuBPz yHCpJdgyzBbx0nsAc9QgZW87nAn1jEDg4d/Wo42hDqUWr8+yvtCMPhULD3+BZG2Oie ElkNXvxNs1I0BZm67/yZwDr7Rv6ti/MAblPee+0lf8KbmIWxBhEflKuFxSrqB37l82 CGA/kgO5cW6hAsk5dTLTrXHeqwIRcuk8btez7hGCF8WntkdR0BjjvUF/QjOtdBdPSd AXWHuBGrqqRfw== Message-ID: <1acb7ba0-6aff-4d30-9554-283ac8fbc93f@kernel.org> Date: Thu, 30 Jul 2026 14:39:51 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/page_reporting: Add page_reporting_delay_ms module parameter To: "Lorenzo Stoakes (ARM)" , Pratyush Mallick Cc: akpm@linux-foundation.org, vbabka@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 References: <20260727230545.262579-1-pratmal@google.com> <91b61f02-c533-41b9-b680-7de52a5c6918@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: EB65710000A X-Stat-Signature: mtr1t9se91acbhw3bgutisa13eiin6pj X-HE-Tag: 1785415198-799191 X-HE-Meta: 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 WB65TjwW kGOtMHq3NcITZwmHC0OPbqwaap8B05bR/0tPa7ek4sXhoN5WLimemBPHrON1it26RjmCHmF7eJRGsj+quHQqFz9XCo7WrYo6YE5G+EHQ9KTI0ZM09601ikzOuYhARuDQb+qWxGkVhD/s8iDtIxibu+thU9Lt3bdVd5KQfoxthROXR68SOtBk1lgNjgLHh18cX/YPV59sEa+wg1YDVEZg3xFtpm0wpnwJ8TzReSIicHuWcK0Fz8KffGfKJLvmKW8xgF9JLBVCgXHBNzhWGUfkKNzDeii2J/fsmRbpa1nkKsLveZmNPEj5tdtt/8Q== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: >>> With 2s, we wait 2s before we start reporting immediately by kicking the >>> workqueue immediately. >>> >>> So "0" does not mean "report all the time", rather "start reporting immediately >>> as we are notified about a pageblock to report". > > No, it's whenever pageblock_order is specified, defaulting to a pageblock. > > But I guess in practice fine. > > There's fun like this in virtio_balloon.c btw: > > /* > * The default page reporting order is @pageblock_order, which > * corresponds to 512MB in size on ARM64 when 64KB base page > * size is used. The page reporting won't be triggered if the > * freeing page can't come up with a free area like that huge. > * So we specify the page reporting order to 5, corresponding > * to 2MB. It helps to avoid THP splitting if 4KB base page > * size is used by host. > * > * Ideally, the page reporting order is selected based on the > * host's base page size. However, it needs more work to report > * that value. The hard-coded order would be fine currently. > */ > #if defined(CONFIG_ARM64) && defined(CONFIG_ARM64_64K_PAGES) > vb->pr_dev_info.order = 5; > #endif Yes, it's really about "a large chunk of memory was freed". On 64k " a large chunk" is unfortunately order 5 == 2MiB (so the same as on 4k where a pageblock is 2M). -- Cheers, David