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 BC52F47DD73 for ; Thu, 20 Aug 2026 17:46:22 +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=1787247983; cv=none; b=lWEDC/pB33wi7XXkygTVn+OonxEu4duXOCaCHfWzQmc/uRR9r0z37B+HLsidnnttvJeOivRBNdBfifnD1ks2W0eO9S52BYbUodYGFIHfKsWeIVfAMckUMqzmnADU4t/MdM3OkQ+XWXytW0Gg9JfFN/7kjh1C1Eu69svX+yrxmug= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787247983; c=relaxed/simple; bh=3PcM2nF496kH0NVRGkSVtqPVZZi3P/R0A3s+Pfy6JHs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=bShA780/ZVQKWfbrDLHcRSFAq0qW59O5aLdFRdxC0xMabqsanTf2DnxLAeJ2xpW5Gi5aphRUbFLCh5jWehRoWD+q7WoWn0fVn07ZUB9avTglI29FIOKiE4UAljt22GsVuO6B4V5trFTh/HE1vsTSSwpSm4u4wG+Vjnbmgv85bK0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UsCwLrRV; 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="UsCwLrRV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7317A1F000E9; Thu, 20 Aug 2026 17:46:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787247982; bh=2fIdalCmTaw2AjswTgZRpQgDXscO6AG89u3FfnnHiks=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=UsCwLrRV/K35zxbIA/hIc4Id6aozHPhPLOrJUiwPAl7OYQh1taZ1K0yNEOwgg/SUt nYUi3Hdf40wr/zFLSUOd6i/TOIIK06CsD7c76CpQ+3D1YmCqljd8DdsVwbaROCzkoN bENSolqCbH0aTMxV0Uodq/7fc051LdApcEbUX5xvVe+cCt1M8fnsy4r4oEb3MGJB7Q qX5rvlwvW6KxieSCMpPyqv8bCjsxXbYmszXW7B/c4r8xxSanuHoPI9dDZ4o+A2i+7T g0mDdl8HXlxn1gl3V37kQt9jiNDzGue/0Wkgo9odCMX7acV9lcZ2eca4XgFmgikc8T J2E591DIchXmA== Message-ID: Date: Thu, 20 Aug 2026 19:46:17 +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 >>> + online_pgcnt++; >> >> Can we avoid these helpers? >> >> const unsigned long subsection = pfn & PAGE_SUBSECTION_MASK; >> >> /* We can have section-sized online holes with VMEMMAP. */ >> if (IS_ENMABLED(CONFIG_SPARSEMEM_VMEMMAP) && >> subsection != last_subsection) { >> is_online = pfn_to_online_page(pfn); >> last_subsection = subsection; >> } >> if (is_online) >> online_pgcnt++; > > 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. > >> An alternative is an inner loop that just walks in SUBSECTION chunks until >> epfn. >> That would probably be even cleaner and faster. >> >> I remember !vmemmap always only has early sections when they are actually >> online. We could extent the comment to clarify that. > > 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. -- Cheers, David