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Mon, 25 Nov 2019 18:22:51 +0000 (UTC) Received: from [10.36.118.6] (unknown [10.36.118.6]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2A8605C1D8; Mon, 25 Nov 2019 18:22:48 +0000 (UTC) Subject: Re: [PATCH v2] mm/memory_hotplug: Don't allow to online/offline memory blocks with holes To: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Dan Williams , Andrew Morton , Michal Hocko , Oscar Salvador , Pavel Tatashin , Anshuman Khandual References: <20191119115237.6662-1-david@redhat.com> <20191125174034.GA41469@freebsd.familie-tometzki.de> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAj4EEwECACgFAljj9eoCGwMFCQlmAYAGCwkI BwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEE3eEPcA/4Na5IIP/3T/FIQMxIfNzZshIq687qgG 8UbspuE/YSUDdv7r5szYTK6KPTlqN8NAcSfheywbuYD9A4ZeSBWD3/NAVUdrCaRP2IvFyELj xoMvfJccbq45BxzgEspg/bVahNbyuBpLBVjVWwRtFCUEXkyazksSv8pdTMAs9IucChvFmmq3 jJ2vlaz9lYt/lxN246fIVceckPMiUveimngvXZw21VOAhfQ+/sofXF8JCFv2mFcBDoa7eYob s0FLpmqFaeNRHAlzMWgSsP80qx5nWWEvRLdKWi533N2vC/EyunN3HcBwVrXH4hxRBMco3jvM m8VKLKao9wKj82qSivUnkPIwsAGNPdFoPbgghCQiBjBe6A75Z2xHFrzo7t1jg7nQfIyNC7ez MZBJ59sqA9EDMEJPlLNIeJmqslXPjmMFnE7Mby/+335WJYDulsRybN+W5rLT5aMvhC6x6POK z55fMNKrMASCzBJum2Fwjf/VnuGRYkhKCqqZ8gJ3OvmR50tInDV2jZ1DQgc3i550T5JDpToh dPBxZocIhzg+MBSRDXcJmHOx/7nQm3iQ6iLuwmXsRC6f5FbFefk9EjuTKcLMvBsEx+2DEx0E UnmJ4hVg7u1PQ+2Oy+Lh/opK/BDiqlQ8Pz2jiXv5xkECvr/3Sv59hlOCZMOaiLTTjtOIU7Tq 7ut6OL64oAq+uQINBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCghCj/CA/lc/LMthqQ773ga uB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseBfDXHA6m4B3mUTWo13nid 0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts6TZ+IrPOwT1hfB4WNC+X 2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiuQmt3yqrmN63V9wzaPhC+ xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKBTccu2AXJXWAE1Xjh6GOC 8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvFFFyAS0Nk1q/7EChPcbRb hJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh2YmnmLRTro6eZ/qYwWkC u8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRkF3TwgucpyPtcpmQtTkWS gDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0LLH63+BrrHasfJzxKXzqg rW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4vq7oFCPsOgwARAQABiQIl BBgBAgAPBQJVy5+RAhsMBQkJZgGAAAoJEE3eEPcA/4NagOsP/jPoIBb/iXVbM+fmSHOjEshl KMwEl/m5iLj3iHnHPVLBUWrXPdS7iQijJA/VLxjnFknhaS60hkUNWexDMxVVP/6lbOrs4bDZ NEWDMktAeqJaFtxackPszlcpRVkAs6Msn9tu8hlvB517pyUgvuD7ZS9gGOMmYwFQDyytpepo YApVV00P0u3AaE0Cj/o71STqGJKZxcVhPaZ+LR+UCBZOyKfEyq+ZN311VpOJZ1IvTExf+S/5 lqnciDtbO3I4Wq0ArLX1gs1q1XlXLaVaA3yVqeC8E7kOchDNinD3hJS4OX0e1gdsx/e6COvy qNg5aL5n0Kl4fcVqM0LdIhsubVs4eiNCa5XMSYpXmVi3HAuFyg9dN+x8thSwI836FoMASwOl C7tHsTjnSGufB+D7F7ZBT61BffNBBIm1KdMxcxqLUVXpBQHHlGkbwI+3Ye+nE6HmZH7IwLwV W+Ajl7oYF+jeKaH4DZFtgLYGLtZ1LDwKPjX7VAsa4Yx7S5+EBAaZGxK510MjIx6SGrZWBrrV TEvdV00F2MnQoeXKzD7O4WFbL55hhyGgfWTHwZ457iN9SgYi1JLPqWkZB0JRXIEtjd4JEQcx +8Umfre0Xt4713VxMygW0PnQt5aSQdMD58jHFxTk092mU+yIHj5LeYgvwSgZN4airXk5yRXl SE+xAvmumFBY Organization: Red Hat GmbH Message-ID: Date: Mon, 25 Nov 2019 19:22:48 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20191125174034.GA41469@freebsd.familie-tometzki.de> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-MC-Unique: DCO4p2IWPsuDW8zpQ67Y5g-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 25.11.19 18:40, Damian Tometzki wrote: > On Tue, 19. Nov 12:52, David Hildenbrand wrote: >> Our onlining/offlining code is unnecessarily complicated. Only memory >> blocks added during boot can have holes (a range that is not >> IORESOURCE_SYSTEM_RAM). Hotplugged memory never has holes (e.g., see >> add_memory_resource()). All memory blocks that belong to boot memory are >> already online. >> >> Note that boot memory can have holes and the memmap of the holes is marked >> PG_reserved. However, also memory allocated early during boot is >> PG_reserved - basically every page of boot memory that is not given to the >> buddy is PG_reserved. >> >> Therefore, when we stop allowing to offline memory blocks with holes, we >> implicitly no longer have to deal with onlining memory blocks with holes. >> E.g., online_pages() will do a >> walk_system_ram_range(..., online_pages_range), whereby >> online_pages_range() will effectively only free the memory holes not >> falling into a hole to the buddy. The other pages (holes) are kept >> PG_reserved (via move_pfn_range_to_zone()->memmap_init_zone()). >> >> This allows to simplify the code. For example, we no longer have to >> worry about marking pages that fall into memory holes PG_reserved when >> onlining memory. We can stop setting pages PG_reserved completely in >> memmap_init_zone(). >> >> Offlining memory blocks added during boot is usually not guaranteed to work >> either way (unmovable data might have easily ended up on that memory during >> boot). So stopping to do that should not really hurt. Also, people are not >> even aware of a setup where onlining/offlining of memory blocks with >> holes used to work reliably (see [1] and [2] especially regarding the >> hotplug path) - I doubt it worked reliably. >> >> For the use case of offlining memory to unplug DIMMs, we should see no >> change. (holes on DIMMs would be weird). >> >> Please note that hardware errors (PG_hwpoison) are not memory holes and >> are not affected by this change when offlining. >> >> [1] https://lkml.org/lkml/2019/10/22/135 >> [2] https://lkml.org/lkml/2019/8/14/1365 >> >> Reviewed-by: Dan Williams >> Cc: Andrew Morton >> Cc: Michal Hocko >> Cc: Oscar Salvador >> Cc: Pavel Tatashin >> Cc: Dan Williams >> Cc: Anshuman Khandual >> Signed-off-by: David Hildenbrand >> --- >> >> This patch was part of: >> [PATCH v1 00/10] mm: Don't mark hotplugged pages PG_reserved >> (including ZONE_DEVICE) >> -> https://www.spinics.net/lists/linux-driver-devel/msg130042.html >> >> However, before we can perform the PG_reserved changes, we have to fix >> pfn_to_online_page() in special scenarios first (bootmem and devmem falling >> into a single section). Dan is working on that. >> >> I propose to give this patch a churn in -next so we can identify if this >> change would break any existing setup. I will then follow up with cleanups >> and the PG_reserved changes later. >> >> --- >> mm/memory_hotplug.c | 28 ++++++++++++++++++++++++++-- >> 1 file changed, 26 insertions(+), 2 deletions(-) >> >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >> index 46b2e056a43f..fc617ad6f035 100644 >> --- a/mm/memory_hotplug.c >> +++ b/mm/memory_hotplug.c >> @@ -1455,10 +1455,19 @@ static void node_states_clear_node(int node, struct memory_notify *arg) >> node_clear_state(node, N_MEMORY); >> } >> >> +static int count_system_ram_pages_cb(unsigned long start_pfn, >> + unsigned long nr_pages, void *data) >> +{ >> + unsigned long *nr_system_ram_pages = data; >> + >> + *nr_system_ram_pages += nr_pages; >> + return 0; >> +} >> + > Hello David, > > what is the meaning of the function ? The return is every time 0. > > I dont understand it ? > Hi Damian, please see how these callbacks are used within walk_system_ram_range(). A return value of 0 only means "don't stop iterating", the actual values are returned via the "void *data" parameter in this instance. Cheers! -- Thanks, David / dhildenb