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 5BCFB36308E for ; Wed, 26 Aug 2026 09:06:31 +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=1787735193; cv=none; b=cPxTYs9ill7DxjzFb8h6Ez0gWR4eOE22tuk2iaWw0B+GFGnc7z+4JGiw34j8AjVsDNF0vGldArD25uu5S38WFZzuZwt0GIkB8NViH4i5/+HlXMk6uBYlXgb7sZLQtl3Lktb4JZOmb/IkD9OuEsGzUDSLlkKHcCVI6JFSL/ZXqqQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787735193; c=relaxed/simple; bh=3/iyfZDbzqazD2HFao0wqSMIfve2ptjST8MKcplaPEM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=iE+HFctnp8MuzkMKvlz1py/qwITIAw+tDSTNNdQu7cKsZF4VoEKPxM3q6IZqS8YUzYpCENDJiqNve0qD/LQrYxUgHfIE4OCXe3xPYQX0SUlhBBhJEtL5NRskMg1cu/xPunpaN3H9SiwUVD0nJGMrUQoaTJO1v83W1TS/yGdY+uI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Db8eitT4; 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="Db8eitT4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C53171F000E9; Wed, 26 Aug 2026 09:06:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787735191; bh=xif2Q2bWA61yFoe3xlnqfvMwm3Fzd4eNOw/v0/j4IUs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Db8eitT43zkxTQ0tnZ30RXDVmrEY5w16260uJUMWz//E/eeLQbEVqgO/gcd8sdOQ6 cXQxRKiQ7vHFxA80EbPJoVkWnX4e9K+090XZW7LLvIlizJB/uJMb4Ln2x3P0jhzChc vQQzZ5IHrY/bVYEviOTrthsjNuZeZooe+KWunOpbHjAeHZOOBsasEHFRKZiTq3XR89 qcDcwWZfFRQs4IfMvHY970IRQM/cfivgxbajHtDo+SNewAc1zy+vfDsgkuRDDKyghm D+FR64X7oBQvm4wVotbT788ttAGA9aNM/rGyq2j+PavBRT1g20xVCLdrZexIHwjdVG 03C+rqLuiXrJw== Message-ID: <819cc4b4-1855-4dbc-adb4-3b18d6fa2924@kernel.org> Date: Wed, 26 Aug 2026 11:06:26 +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 v7 2/2] mm/memory_hotplug: optimize zone contiguous check when changing pfn range To: "Liu, Yuan1" , Oscar Salvador , Mike Rapoport , Wei Yang Cc: "linux-mm@kvack.org" , "Zou, Nanhai" , Chen Zhang , "Zeng, Jason" , "Chen, Yu C" , "Deng, Pan" , "Li, Tianyou" , "linux-kernel@vger.kernel.org" References: <20260818085702.3395529-1-yuan1.liu@intel.com> <20260818085702.3395529-3-yuan1.liu@intel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/21/26 05:17, Liu, Yuan1 wrote: >> -----Original Message----- >> From: David Hildenbrand (Arm) >> Sent: Friday, August 21, 2026 1:46 AM >> To: Liu, Yuan1 ; Oscar Salvador ; >> Mike Rapoport ; Wei Yang >> Cc: linux-mm@kvack.org; Zou, Nanhai ; Chen Zhang >> ; Zeng, Jason ; Chen, Yu C >> ; Deng, Pan ; Li, Tianyou >> ; linux-kernel@vger.kernel.org >> Subject: Re: [PATCH v7 2/2] mm/memory_hotplug: optimize zone contiguous >> check when changing pfn range >> >>> >>> I think there may be an issue here: PAGE_SUBSECTION_MASK is not >>> defined when CONFIG_FLATMEM is enabled, which would result in a >>> build failure. >> >> Ah, yeah. >> >>> >> until >> actually >>> >>> Hi David >>> >>> What about the following approach? It removes the helper and changes >>> the per-PFN online check to a per-chunk check. >>> >>> + u64 pgcnt = 0, online_pgcnt = 0; >>> +#ifdef CONFIG_SPARSEMEM_VMEMMAP >>> + const unsigned long chunk = PAGES_PER_SUBSECTION; >>> +#else >>> + const unsigned long chunk = epfn - spfn; >>> +#endif >>> >>> - for_each_valid_pfn(pfn, spfn, epfn) { >>> - __init_single_page(pfn_to_page(pfn), pfn, zone, node); >>> - __SetPageReserved(pfn_to_page(pfn)); >>> - pgcnt++; >>> + /* >>> + * With VMEMMAP, subsection-sized holes can exist, and PFNs >> within >>> + * these holes can fail pfn_to_online_page(). Without VMEMMAP, >> we >>> + * always only have early sections when they are actually >> online. >>> + */ >>> + for (pfn = spfn; pfn < epfn; pfn += chunk) { >>> + const unsigned long chunk_epfn = min(pfn + chunk, epfn); >>> + const bool is_online >> = !IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) || >>> + pfn_to_online_page(pfn); >>> + unsigned long p; >>> + >>> + for_each_valid_pfn(p, pfn, chunk_epfn) { >>> + __init_single_page(pfn_to_page(p), p, zone, >> node); >>> + __SetPageReserved(pfn_to_page(p)); >>> + if (is_online) >>> + online_pgcnt++; >>> + pgcnt++; >>> + } >> >> I'd keep the for_each_valid_pfn() the outer loop. > > Hi David > > Do you mean the following approach? We use for_each_valid_pfn as > the outer loop and, with VMEMMAP,check online PFNs > in PAGES_PER_SUBSECTION chunks > > +#ifdef CONFIG_SPARSEMEM_VMEMMAP > + const unsigned long chunk = PAGES_PER_SUBSECTION; > +#else > + const unsigned long chunk = epfn - spfn; > +#endif > + unsigned long pfn, next_chunk_pfn = spfn; > + u64 pgcnt = 0, online_pgcnt = 0; > + bool is_online = true; > > for_each_valid_pfn(pfn, spfn, epfn) { > __init_single_page(pfn_to_page(pfn), pfn, zone, node); > __SetPageReserved(pfn_to_page(pfn)); > + > + /* > + * With VMEMMAP, subsection-sized holes can exist, and PFNs > + * within these holes can fail pfn_to_online_page(). Without > + * VMEMMAP, early sections only exist when actually online. > + */ > + if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) && > + pfn >= next_chunk_pfn) { > + is_online = !!pfn_to_online_page(pfn); > + next_chunk_pfn = min(pfn + chunk, epfn); > + } > + if (is_online) > + online_pgcnt++; > + It's hard to get it any cleaner. I was wondering whether we should just have a separate for_each_online_pfn() call afterwards, but that's also not ideal. I was wondering whether we should also just use pfn_section_valid() directly. Something like the following: diff --git a/mm/mm_init.c b/mm/mm_init.c index e9c4204b73adb..cc7d55a71a060 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -838,22 +838,39 @@ overlap_memmap_init(unsigned long zone, unsigned long *pfn) * zone/node above the hole except for the trailing pages in the last * section that will be appended to the zone/node below. */ -static void __init init_unavailable_range(unsigned long spfn, - unsigned long epfn, - int zone, int node) +static unsigned long __init init_unavailable_range(unsigned long spfn, + unsigned long epfn, + int zone, int node) { + unsigned long next_chunk_pfn __maybe_unused = spfn; unsigned long pfn; - u64 pgcnt = 0; + u64 online_pgcnt = 0, pgcnt = 0; + bool is_online = true; for_each_valid_pfn(pfn, spfn, epfn) { __init_single_page(pfn_to_page(pfn), pfn, zone, node); __SetPageReserved(pfn_to_page(pfn)); pgcnt++; + + /* + * With vmemmap, at this stage all pages in an early section + * have a valid memmap and are marked as online. However, only + * subsections in the subsection map are actually online. + */ +#ifdef CONFIG_SPARSEMEM_VMEMMAP + if (pfn >= next_chunk_pfn) { + is_online = pfn_section_valid(__pfn_to_section(pfn), pfn); + next_chunk_pfn = min(SUBSECTION_ALIGN_UP(pfn + 1), epfn); + } +#endif + if (is_online) + online_pgcnt++; } if (pgcnt) pr_info("On node %d, zone %s: %lld pages in unavailable ranges\n", node, zone_names[zone], pgcnt); + return online_pgcnt; } /* I'd love to avoid any CONFIG_SPARSEMEM_VMEMMAP, but that's hard as well :) -- Cheers, David