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t=1787155079; bh=pgQJx1AdlduwHjKt1bqT1KprZQI76dNWF4lNFIEKvWk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=C0fgsA+2ztb2d9rph6EjHyxIYz1Iz0QdEDMFkrqatm+trbZdkCl61C1tA0EGPVX9M vcSQ5TVgr19KbZMVffQLAXugJVTWq4L33vBRDuLZJB9uas/Nadhwr0OjE3Y8T4JdZ4 m/7ThuYfPZHhl2r4gin88rouDtF158cCt1yFM0c05cgryYi6RYwa5WH1bhvfzbEKVp DPwtlzdc8zLWf91dftIY+6n170P1SVIpJfoTkMEtp579rJSMGnmoRrNK0yQdCign+G vKnto5ZVO05M29TCjkrn0mFdEPUGvKDPIXudi1kdB4+8sNq29qRFOP/PmW1hDmzr7P 7aIU1KJcGZPMg== Message-ID: <0a6186b2-0e0c-4d6b-a3e1-c5e5cb75d669@kernel.org> Date: Wed, 19 Aug 2026 17:57:53 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 1/2] mm/memory_hotplug: optimize zone contiguous check when changing pfn range To: Wei Yang Cc: "Liu, Yuan1" , Oscar Salvador , Mike Rapoport , "linux-mm@kvack.org" , "Zou, Nanhai" , "Deng, Pan" , "Li, Tianyou" , Chen Zhang , "Zeng, Jason" , "linux-kernel@vger.kernel.org" References: <20260723084946.189392-1-yuan1.liu@intel.com> <20260723084946.189392-2-yuan1.liu@intel.com> <2cbd42e1-b5bb-474c-b0e7-ce3f46541891@kernel.org> <0b02ef3e-363f-4b49-a208-54cdfea56c75@kernel.org> <01795519-54e8-4ed8-a94e-2b77780abc3a@kernel.org> <20260815015532.ei4abygk4erdtlhh@master> 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-Rspamd-Queue-Id: CDA81140005 X-Rspam-User: X-Stat-Signature: 6d99yz3wk9b8aha1zs4chomw3ahicpzr X-Rspamd-Server: rspam06 X-HE-Tag: 1787155080-17085 X-HE-Meta: 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 iJU242MZ 8FmUCjW5M1B1glTUtdiV6X3oyT3WNqND24P7pxMDIiP/a+KP/SE8gLNoB0klRvRzfPFG2J468xPJXDpD3EyMb3n/pg3EfgVFl4g6g9K7B0pxsajLDry3reXVlkFDIOi2A646u65dJySagcmRg+/COGSFSiOK3HnBrdAfmxYSTk8KNX9CtK0xcSCpAX4IU37UTjn547U+cF5jjyWrV8vp6s/tHYv5sHyVZX4G0T2PnyWwPJDSF9jbE9TgfbMPppnbS8yCGu3jd3AqBINHLPciE4Uey+ZSnSiibTcqDIHZWd1K53RtYjUnbI4XP3O6alwu3QiZJS4IopwSqiuJXRBQSh+SraIkNIJIKoV/c3ybavUq6z6CGlWzFxlL4IoBcHsjRsDZP/liq03oqFzm3B0DDY5yKuevUwyBn3bqdppoRDKFSO24= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/15/26 03:55, Wei Yang wrote: > On Tue, Aug 11, 2026 at 02:23:18PM +0200, David Hildenbrand (Arm) wrote: >> On 8/10/26 16:04, David Hildenbrand (Arm) wrote: >>> >>> Thanks for reminding me. I think the right direction is to finally clean up the >>> pfn_valid() handling. >>> >>> Let me take a stab at just having pfn_valid() / for_each_valid_pfn() respecting >>> the subsection map. >> >> ... and that turns complicated very quickly. The problem is that we have some users, >> in particular the buddy, that just assumes that MAX_PAGE_ORDER regions are fully >> accessible. >> >> The fun begins once we have MAX_PAGE_ORDER span multiple subsections. So we'd actually >> want to initialize the memmap. >> >> The pfn_valid() vs. pfn_to_online_page() inconsistency is really nasty :( >> > > One thing I'd like to confirm. > > pfn_to_online_page() is expected to return an "online page", which is in > buddy, right? > >> I mean, in init_unavailable_range() we could actually figure out fairly easily >> whether we are dealing with holes where pfn_to_online_page() would succeed. >> >> diff --git a/mm/mm_init.c b/mm/mm_init.c >> index e9c4204b73adb..54e71e17f2c3c 100644 >> --- a/mm/mm_init.c >> +++ b/mm/mm_init.c >> @@ -843,11 +843,13 @@ static void __init init_unavailable_range(unsigned long spfn, >> int zone, int node) >> { >> unsigned long pfn; >> - u64 pgcnt = 0; >> + u64 pgcnt = 0, online_pgcnt = 0; >> >> for_each_valid_pfn(pfn, spfn, epfn) { >> __init_single_page(pfn_to_page(pfn), pfn, zone, node); >> __SetPageReserved(pfn_to_page(pfn)); >> + if (pfn_to_online_page(pfn)) >> + online_pgcnt++; > > But a hole in early section could still return a valid page if the hole > is less than a subsection. > > Is this an expected behavior? Essentially, pfn_valid() is always true for early sections. pfn_to_online_page() is only true in only section only for parts marked in the subsection map. So if you have a hole that covers a subsection, it is not marked in the subsection map, pfn_valid() would be true and for_each_valid_pfn() would iterate it, whereby pfn_to_online_page() will reject it. Zone shrinking will later simply skip that hole, because !pfn_to_online_page(). -- Cheers, David