From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) (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 26AC4539763 for ; Wed, 14 Oct 2026 14:28:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=96.67.55.147 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791988120; cv=none; b=I5hTmS4INoPhkEzBe+ApH/P75UgIHC1xvMuuaKce63sZvyj9eQeeWnUGwu2OUD0GJE/J9tnfSHBNMr++c57OVHKxfHq3lOUp1X8n8eeAfx7w/eIWMIEDtZ1nTsp4crZBEiEW6pln1Cc9T1HQc6bEAOKzmU2bYKCM4sVqTfy+FjU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791988120; c=relaxed/simple; bh=3Gc27KaESD4Zm5M8W+YEErJ2deocBptMWNskB4QSf8s=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=ui2XaqmW1NTbSvjwPsn8O/MuptJdy+JFPj+kCzzzgzJ6RgxIrDtshdLIlm+rTj1OR+pmoWCxhy84O2SCdf004/kWE2PVW3l/ECXEBDCQNM4Mryz4tSa/0lK+lg1XnR9T5uDvUTZzODhtPioudQT+FoHAeIvC4SoNuYNG+QwxvxU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=surriel.com; spf=pass smtp.mailfrom=surriel.com; dkim=pass (2048-bit key) header.d=surriel.com header.i=@surriel.com header.b=nHaT7scX; arc=none smtp.client-ip=96.67.55.147 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=surriel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=surriel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=surriel.com header.i=@surriel.com header.b="nHaT7scX" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=surriel.com ; s=mail; h=MIME-Version:Content-Transfer-Encoding:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID; bh=rsATh2NvdfjYssyKDxNkJtZ2YWaOMp/Hif/9TBiSHDk=; b=nHaT7s cXU1WXU6CO3hd6w6vappdCuPeAFBZCKamSkG2eanWhFG5ef7XFK4lpomusUIbqBABgVlsT+XlXteg 2mMFrQwqUTSZ9kP3F3MsFx2A46M9MTDc0ndj67/y9ni7/JAghqLwhiddCULH6Q1yu9ZYtETTjkeNO WqIwl2/gjC7jTKra5m8FJ7seZU+T8PpPCqCVXYaxUZb9Vueaa3fHz56WJjILh7DU5BUqAW2ypWDkV gdUF9yM1Esri2XdhHpZmMBTMs/xp+eYfN2JpZuGXTwufa6A/eDVi17XuSoPr8uVW145eIVfTcsiq4 ANwzrdEJzrUvdGynMUHv6rgUtkSg==; Received: from [2601:18c:8100:a0e0:2541:b86e:2586:d219] by shelob.surriel.com with esmtpsa (TLS1.3) tls TLS_AES_256_GCM_SHA384 (Exim 4.99.5) (envelope-from ) id 1xGzxS-00000007OmE-0fd6; Wed, 14 Oct 2026 14:27:54 +0000 Message-ID: <038db2e68469e74077264a490e104391bdffe35e.camel@surriel.com> Subject: Re: [RFC PATCH 2/5] mm/page_alloc: count a merged buddy's pages under the merged type From: Rik van Riel To: Dev Jain , linux-kernel@vger.kernel.org Cc: Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Kairui Song , Qi Zheng , Shakeel Butt , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , linux-mm@kvack.org Date: Wed, 14 Oct 2026 10:27:54 -0400 In-Reply-To: <55f51fb8-9777-424a-b45f-a6a5bd9a4693@arm.com> References: <20261007021250.1665929-1-riel@surriel.com> <20261007021250.1665929-3-riel@surriel.com> <55f51fb8-9777-424a-b45f-a6a5bd9a4693@arm.com> Autocrypt: addr=riel@surriel.com; prefer-encrypt=mutual; keydata=mQENBFIt3aUBCADCK0LicyCYyMa0E1lodCDUBf6G+6C5UXKG1jEYwQu49cc/gUBTTk33A eo2hjn4JinVaPF3zfZprnKMEGGv4dHvEOCPWiNhlz5RtqH3SKJllq2dpeMS9RqbMvDA36rlJIIo47 Z/nl6IA8MDhSqyqdnTY8z7LnQHqq16jAqwo7Ll9qALXz4yG1ZdSCmo80VPetBZZPw7WMjo+1hByv/ lvdFnLfiQ52tayuuC1r9x2qZ/SYWd2M4p/f5CLmvG9UcnkbYFsKWz8bwOBWKg1PQcaYHLx06sHGdY dIDaeVvkIfMFwAprSo5EFU+aes2VB2ZjugOTbkkW2aPSWTRsBhPHhV6dABEBAAG0HlJpayB2YW4gU mllbCA8cmllbEByZWRoYXQuY29tPokBHwQwAQIACQUCW5LcVgIdIAAKCRDOed6ShMTeg05SB/986o gEgdq4byrtaBQKFg5LWfd8e+h+QzLOg/T8mSS3dJzFXe5JBOfvYg7Bj47xXi9I5sM+I9Lu9+1XVb/ r2rGJrU1DwA09TnmyFtK76bgMF0sBEh1ECILYNQTEIemzNFwOWLZZlEhZFRJsZyX+mtEp/WQIygHV WjwuP69VJw+fPQvLOGn4j8W9QXuvhha7u1QJ7mYx4dLGHrZlHdwDsqpvWsW+3rsIqs1BBe5/Itz9o 6y9gLNtQzwmSDioV8KhF85VmYInslhv5tUtMEppfdTLyX4SUKh8ftNIVmH9mXyRCZclSoa6IMd635 Jq1Pj2/Lp64tOzSvN5Y9zaiCc5FucXtB9SaWsgdmFuIFJpZWwgPHJpZWxAc3VycmllbC5jb20+iQE +BBMBAgAoBQJSLd2lAhsjBQkSzAMABgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAAKCRDOed6ShMTe g4PpB/0ZivKYFt0LaB22ssWUrBoeNWCP1NY/lkq2QbPhR3agLB7ZXI97PF2z/5QD9Fuy/FD/jddPx KRTvFCtHcEzTOcFjBmf52uqgt3U40H9GM++0IM0yHusd9EzlaWsbp09vsAV2DwdqS69x9RPbvE/Ne fO5subhocH76okcF/aQiQ+oj2j6LJZGBJBVigOHg+4zyzdDgKM+jp0bvDI51KQ4XfxV593OhvkS3z 3FPx0CE7l62WhWrieHyBblqvkTYgJ6dq4bsYpqxxGJOkQ47WpEUx6onH+rImWmPJbSYGhwBzTo0Mm G1Nb1qGPG+mTrSmJjDRxrwf1zjmYqQreWVSFEt26tBpSaWsgdmFuIFJpZWwgPHJpZWxAZmIuY29tP okBPgQTAQIAKAUCW5LbiAIbIwUJEswDAAYLCQgHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQznneko TE3oOUEQgAsrGxjTC1bGtZyuvyQPcXclap11Ogib6rQywGYu6/Mnkbd6hbyY3wpdyQii/cas2S44N cQj8HkGv91JLVE24/Wt0gITPCH3rLVJJDGQxprHTVDs1t1RAbsbp0XTksZPCNWDGYIBo2aHDwErhI omYQ0Xluo1WBtH/UmHgirHvclsou1Ks9jyTxiPyUKRfae7GNOFiX99+ZlB27P3t8CjtSO831Ij0Ip QrfooZ21YVlUKw0Wy6Ll8EyefyrEYSh8KTm8dQj4O7xxvdg865TLeLpho5PwDRF+/mR3qi8CdGbkE c4pYZQO8UDXUN4S+pe0aTeTqlYw8rRHWF9TnvtpcNzZw== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2026-10-14 at 19:46 +0530, Dev Jain wrote: >=20 >=20 > > +++ b/mm/page_alloc.c > > @@ -993,6 +993,11 @@ static inline void __free_one_page(struct page > > *page, > > =C2=A0 account_freepages(zone, 1 << order, > > migratetype); > > =C2=A0 } else { > > =C2=A0 __del_page_from_free_list(buddy, zone, > > order, buddy_mt); > > + /* The buddy's free pages join the merged > > block's type. */ > > + if (unlikely(buddy_mt !=3D migratetype)) { > > + account_freepages(zone, -(1 << > > order), buddy_mt); > > + account_freepages(zone, 1 << > > order, migratetype); > > + } > > =C2=A0 } > > =C2=A0 >=20 > MAX_PAGE_ORDER > pageblock_order confuses things so much : ( I'm not a fan, either. It trips me up every time. >=20 > Sashiko raises something: > https://sashiko.dev/#/patchset/20261007021250.1665929-1-riel%40surriel.co= m >=20 > Although feels like it is exaggerating. I suppose if we switch the two lines around, doing the increment on migratetype before decrementing buddy_mt we could avoid that transient underflow? >=20 > My concern is for systems with a high diff between MAX_PAGE_ORDER and > pageblock_order. So on arm64 systems with 64K pagesize but pageblock > size as 2M (and PMD size 512M), the pageblock order is 5. We use this > configuration to reliably get TLB optimization from contpte size > mappings. >=20 > Will we then repeatedly overflow the pcpu counter into the zone > counter, > regressing stuff? The per_cpu_pages struct does not seem to keep counts on a per migratetype basis at all. It has per migratetype lists, but only one pcp->count. Also doesn't the pcp only carry order zero pages currently? I don't really understand your worry. >=20 > Perhaps I am overthinking. Your approach is clean, but perhaps we > could > also do: >=20 > void account_freepages_move(zone, order, buddy_mt, mt) >=20 > /* PCP-types do not have per-migratetype free counts. */ > if (likely (buddy_mt < MIGRATE_PCPTYPES && mt < > MIGRATE_PCPTYPES)) > return; Wouldn't that throw off the counts when we merge e.g. a MIGRATE_UNMOVABLE page with a MIGRATE_MOVABLE buddy? With your test we would only ever do the free count adjustment for mismatched types if one of the pages was HIGHATOMIC or CMA. That leaves the common case without coverage. --=20 All Rights Reversed.