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t=1786101925; bh=p9g/3Te/DMFHNFPb4/a0KQzBfiLfVixcDYjY5aWEY8w=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=NvusTGElGc15NdCe6mq7jvl8yLc7zLopyx8UbB+CZrfb65Qb1e75iWo297AFC7XlQ Fy2xdG7WvrmFgs2zq5t4g2/IPIdQC5O9ezNn9euxKMG5qAFQ5mbe6iyUey8U8ck/91 rmd0ak1G7ieSu9a2734ItLITpZL5k5RUxsW1JKziGteJU/d1Cg8xbUlVbFHjWJo2sU N1o9iK6RgRB7kPOOLB4mvTbr2f/01HD1q335jV53pSPh5tBsM0nWJZtbBCd+zdc4PL 6Qr421mbamMmmMV8YeSOApwyMT8CXzNBK7QkhajnFv6ca8Sr45Ibgmn+BnJPhdWDaH AHaoHELbxhFhA== Message-ID: Date: Fri, 7 Aug 2026 13:25:20 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 2/2] mm/memory_hotplug: improve shrink_zone_span() subsection boundary checks To: Wei Yang Cc: Yuan Liu , Oscar Salvador , Mike Rapoport , linux-mm@kvack.org, Nanhai Zou , Pan Deng , Tianyou Li , Chen Zhang , Jason Zeng , linux-kernel@vger.kernel.org References: <20260723084946.189392-1-yuan1.liu@intel.com> <20260723084946.189392-3-yuan1.liu@intel.com> <20260807032205.ykhxbapx6nhg5hpt@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: 7C9EC140003 X-Stat-Signature: qefh1yss96g5xn9gsyersw9wapd4fgyk X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1786101926-445959 X-HE-Meta: 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 dGlnqoOb BeGTdNy0N4Ojyy19jUXtwW2yuQ0gwoqU9pdrefHZbF1klCpXLnNaJyVPcpjwmqg2OApQRm4s7MHsDyWUIvoO+MpcLS4lEkHMbW4VRTdkpkbZAE8gTJQKstl322r/l/YUr8eU3TylRx6I7ec02wtnD8DLxVoVD7ZfTRLE4Xp2ZNHqXfPLF8oBIqFXayBChljt2NigiapfHVHF9jPCeKqMW4ECKPje4/vPX7aUnlPGVQd7LeX274Y6sOsBNtcTlgvLZo1Ytb77sdjtEQHlZjUAQfV+FwEzCMJp/9r24oKPn0vdgKIzrgU/TPlrNBauCQtUazo5DrUneiCh+oDt1hX2nNEJ8+LKrEqXet2FVqGZCkFqA0p/OHx2RW/hs02oCGcKzj+/qHLqLcwhvOTULR9jGM1zU1B9aBrQ3AY9wUztH3BCtwkk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/7/26 05:22, Wei Yang wrote: > On Wed, Aug 05, 2026 at 01:02:29PM +0200, David Hildenbrand (Arm) wrote: >> On 7/23/26 10:49, Yuan Liu wrote: >>> When shrinking a zone span after removing a PFN range, >>> find_smallest_section_pfn() and find_biggest_section_pfn() >>> only checked one edge PFN in each subsection for nid/zone matching. >>> >>> If a memory or hole boundary falls in the middle of a subsection, >>> that edge PFN may belong to a different nid/zone, causing the helpers >>> to miss a valid PFN within that subsection. >>> >>> Fix this by checking both subsection edge PFNs for nid/zone matching. >>> Keep a single pfn_to_online_page() check per subsection, since online >>> state is the same for all PFNs in a subsection. >>> >>> Reviewed-by: Jason Zeng >>> Signed-off-by: Yuan Liu >>> --- >>> mm/memory_hotplug.c | 42 +++++++++++++++++++++++++++--------------- >>> 1 file changed, 27 insertions(+), 15 deletions(-) >>> >>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >>> index 4c699fd9c479..3a281d595207 100644 >>> --- a/mm/memory_hotplug.c >>> +++ b/mm/memory_hotplug.c >>> @@ -427,17 +427,24 @@ static unsigned long find_smallest_section_pfn(int nid, struct zone *zone, >>> unsigned long start_pfn, >>> unsigned long end_pfn) >>> { >>> - for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SUBSECTION) { >>> - if (unlikely(!pfn_to_online_page(start_pfn))) >>> - continue; >>> + unsigned long next_pfn; >>> >>> - if (unlikely(pfn_to_nid(start_pfn) != nid)) >>> - continue; >>> + for (; start_pfn < end_pfn; start_pfn = next_pfn) { >>> + unsigned long tail_pfn; >>> >>> - if (zone != page_zone(pfn_to_page(start_pfn))) >>> + next_pfn = start_pfn + PAGES_PER_SUBSECTION; >>> + tail_pfn = next_pfn - 1; >>> + >>> + if (unlikely(!pfn_to_online_page(start_pfn))) >>> continue; >>> >>> - return start_pfn; >>> + if (likely(pfn_to_nid(start_pfn) == nid) && >>> + zone == page_zone(pfn_to_page(start_pfn))) >>> + return start_pfn; >>> + >>> + if (likely(pfn_to_nid(tail_pfn) == nid) && >>> + zone == page_zone(pfn_to_page(tail_pfn))) >>> + return start_pfn; >>> } >>> >>> return 0; >>> @@ -448,21 +455,26 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone, >>> unsigned long start_pfn, >>> unsigned long end_pfn) >>> { >>> - unsigned long pfn; >>> + unsigned long pfn, prev_pfn; >>> >>> /* pfn is the end pfn of a memory section. */ >>> pfn = end_pfn - 1; >>> - for (; pfn >= start_pfn; pfn -= PAGES_PER_SUBSECTION) { >>> - if (unlikely(!pfn_to_online_page(pfn))) >>> - continue; >>> + for (; pfn >= start_pfn; pfn = prev_pfn) { >>> + unsigned long head_pfn; >>> >>> - if (unlikely(pfn_to_nid(pfn) != nid)) >>> - continue; >>> + prev_pfn = pfn - PAGES_PER_SUBSECTION; >>> + head_pfn = prev_pfn + 1; >>> >>> - if (zone != page_zone(pfn_to_page(pfn))) >>> + if (unlikely(!pfn_to_online_page(pfn))) >>> continue; >>> >>> - return pfn; >>> + if (likely(pfn_to_nid(pfn) == nid) && >>> + zone == page_zone(pfn_to_page(pfn))) >>> + return pfn; >>> + >>> + if (likely(pfn_to_nid(head_pfn) == nid) && >>> + zone == page_zone(pfn_to_page(head_pfn))) >>> + return pfn; >>> } >>> >>> return 0; >> >> >> I think improving that should be patch #1. >> >> But I think we can do much better code-wise. What about the following >> cleanup instead: >> >> >> >From 6e9ea094daf8d04c0b119b780572a846334f8164 Mon Sep 17 00:00:00 2001 >> From: "David Hildenbrand (Arm)" >> Date: Wed, 5 Aug 2026 12:52:55 +0200 >> Subject: [PATCH] mm/memory_hotplug: make shrink_zone_span() more robust >> >> Let's make shrink_zone_span() more robust by checking in >> find_smallest_section_pfn() / find_biggest_section_pfn() that start+end >> of the subsection. >> >> While at it, clean up the function heavily, factoring the core check >> out into subsection_overlaps_zone(). >> >> There likely is no need to check for the nid first: we require >> SPARSEMEM_VMEMMAP_ENABLE where pfn_to_page() is cheap, and the >> pfn_to_nid() on CONFIG_NUMA would do a pfn_to_page() either way. So >> let's just drop that for now. >> >> Signed-off-by: David Hildenbrand (Arm) >> --- >> mm/memory_hotplug.c | 59 ++++++++++++++++++--------------------------- >> 1 file changed, 24 insertions(+), 35 deletions(-) >> >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >> index 226ab9cb078ad..79937f9672d01 100644 >> --- a/mm/memory_hotplug.c >> +++ b/mm/memory_hotplug.c >> @@ -425,49 +425,39 @@ int __add_pages(int nid, unsigned long pfn, unsigned long nr_pages, >> return err; >> } >> >> -/* find the smallest valid pfn in the range [start_pfn, end_pfn) */ >> -static unsigned long find_smallest_section_pfn(int nid, struct zone *zone, >> - unsigned long start_pfn, >> - unsigned long end_pfn) >> +static bool subsection_overlaps_zone(unsigned long pfn, struct zone *zone) >> { >> - for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SUBSECTION) { >> - if (unlikely(!pfn_to_online_page(start_pfn))) >> - continue; >> + const unsigned long start_pfn = ALIGN_DOWN(pfn, PAGES_PER_SUBSECTION); >> + const unsigned long end_pfn = start_pfn + PAGES_PER_SUBSECTION - 1; >> >> - if (unlikely(pfn_to_nid(start_pfn) != nid)) >> - continue; >> + /* All pages in a subsection are either online or offline. */ >> + if (unlikely(!pfn_to_online_page(start_pfn))) >> + return false; >> >> - if (zone != page_zone(pfn_to_page(start_pfn))) >> - continue; >> + /* Checking start+end is sufficient. */ >> + return zone == page_zone(pfn_to_page(start_pfn)) || >> + zone == page_zone(pfn_to_page(end_pfn)); >> +} > > Hi, David Hi, > > I am thinking if we could initialize each subsection to only one zone, we may > reduce the complexity? > > For example, in init_unavailable_range() align spfn to subsection and init the > head unaligned part to previous zone? > > Do you think this is reasonable? I'm afraid of opening up another can of worms. :) The additional page_zone(pfn_to_page(end_pfn) check is cheap with VMEMMAP, so I think we should focus on that first. (and the patch is in general a cleanup :) ) -- Cheers, David