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 B4B7C3A0B2E; Fri, 17 Jul 2026 10:29:19 +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=1784284161; cv=none; b=iZCYwKT7nw0vrjaq/Ixw9NGlibbDInSX75ULVNpPxUAkL1bMgzL0W77HLS9w7MncfWVfEltJRifFcRfUtyX55lcyxNAc0wt8eW3QDeudZDFzkpG+6NyvSSo3GTtlSrYWFn87S4BOd5xtNmEtubWvRJIVRDuX6UyQ1zeb3UtiyaY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784284161; c=relaxed/simple; bh=2HToOcZv1T+lM9dO0dd2A4apjhiZwSISh71QgKydfWc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=d5VbGnTKosy2ZZFhw4Y2ZNlKLIdu124lOJXJYXw/SKOmxSaYQsXoIPUgAuo1rr6192gYIFNhcsq4d1y70irKCnhnAeBoWFmjUldYJ0vZxeRz0te755U2jUgiLNPvH9SXTfJAe8Q7SjanbygPz6L1L/TVVuTnxoTUA8iAQ3RpOjQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QX/Zzy4f; 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="QX/Zzy4f" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1B1101F000E9; Fri, 17 Jul 2026 10:29:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784284159; bh=5gkJj8mPn7DXvf10vpMFMt+lKH5hJcxAoz+8Yfk7BJA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=QX/Zzy4fhOl/Rfn6xnO/2b0c0XsiG9jzb2Bxl3fIG1PmBlPJWpflRdzs9oU1Hd7uK LrgePrC5eehD95jM7GQepotJkHH/pZoMMLhXM6utYMmqQm2i76OyKtrJhnjxkuEexz 3Li9npc+Q5i3mQI15i2qVZNrnOyO/llaCVDjBUaGGESvze8Sa9k1+M/cUusl0V8AsV QYl9FocD9ItGf6bGWakbcSu1QfkhjYJOdzIamNXPf1oCVc7oQAj3udWK6+8KwHChjW 1aHxuspgpWpRN+CuGi2ke/qLI5AVSMl7dsThjRU5FzZsxAObriLZb7gmnrb5ueoWpj zv7ocnQ7IDw4w== Message-ID: <676b9fa3-947d-42d2-b4e2-192e372be110@kernel.org> Date: Fri, 17 Jul 2026 12:29:11 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/thp: expose deferred split folio memory usage in meminfo Content-Language: en-US To: Ye Liu , "David Hildenbrand (Arm)" , Greg Kroah-Hartman , "Rafael J. Wysocki" , Danilo Krummrich , Andrew Morton , Lorenzo Stoakes Cc: Ye Liu , "Liam R. Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kairui Song , Qi Zheng , Shakeel Butt , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Lance Yang , Usama Arif , driver-core@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org References: <20260717063025.168436-1-ye.liu@linux.dev> <46017e29-48a3-4a74-8c5a-0be9d912deaa@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 7/17/26 11:31, Ye Liu wrote: > 在 2026/7/17 16:37, David Hildenbrand (Arm) 写道: >> On 7/17/26 08:30, Ye Liu wrote: >>> From: Ye Liu >>> >>> Folios on the deferred split list hold physical memory that is >>> invisible in meminfo. When a THP becomes partially mapped, the >>> unmapped pages are removed from AnonPages but remain physically >>> allocated until the shrinker splits the folio. This creates a >>> memory accounting gap where used memory cannot be attributed to >>> any meminfo field. >>> >>> Add NR_DEFERRED_SPLIT_PAGES to track the total memory consumed by >>> folios currently on the deferred_split_lru, updated via >>> mod_node_page_state() at all enqueue/dequeue points. The new field >>> DeferredSplitPages is visible in /proc/meminfo, /proc/vmstat, and >>> per-node /sys/devices/system/node/node*/meminfo. >>> >> >> Oh no. >> >> This is really exposing a current implementation detail where we have this >> information easily available in a way that we will not be able to change that >> implementation later. >> > > Yes, `/proc/meminfo` is a user-space ABI. > Adding it there means you can't change the semantics, > and the field will become unmaintainable, yet you can't delete it either. > But I think this information is still necessary. > Where would be a better place to put it? I once added KReclaimable to /proc/meminfo, its value used to be SReclaimable plus ION allocator (I think), but that one was later removed so it's now equivalent and I regret adding it and it stays there. If the deferred split folios are just waiting for a memory pressure kick a shrinker to reclaim them, the KReclaimable counter could however be a sensible fit and wouldn't need adding a new user-visible output. However I assume there's tradeoff with having to track this (complexity, overhead) and possibly overhead of reading /proc/meminfo so it's not clear-cut. Just pointing it out as a possibility.