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Thu, 6 Feb 2020 10:03:02 +0000 (UTC) Received: from [10.36.117.188] (ovpn-117-188.ams2.redhat.com [10.36.117.188]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8E9FE26571; Thu, 6 Feb 2020 10:02:56 +0000 (UTC) Subject: Re: [PATCH] mm/hotplug: Adjust shrink_zone_span() to keep the old logic To: Baoquan He Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, richardw.yang@linux.intel.com, mhocko@suse.com, osalvador@suse.de References: <20200206053912.1211-1-bhe@redhat.com> <7ecaf36f-9f70-05bd-05fc-6dec82b7d559@redhat.com> <20200206093530.GO8965@MiWiFi-R3L-srv> <20200206100029.GP8965@MiWiFi-R3L-srv> 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: <9e5ccff5-faa4-837d-7cdb-d94b8b5870a8@redhat.com> Date: Thu, 6 Feb 2020 11:02:53 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: <20200206100029.GP8965@MiWiFi-R3L-srv> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 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 06.02.20 11:00, Baoquan He wrote: > On 02/06/20 at 10:48am, David Hildenbrand wrote: >> On 06.02.20 10:35, Baoquan He wrote: >>> On 02/06/20 at 09:50am, David Hildenbrand wrote: >>>> On 06.02.20 06:39, Baoquan He wrote: >>>>> In commit 950b68d9178b ("mm/memory_hotplug: don't check for "all holes" >>>>> in shrink_zone_span()"), the zone->zone_start_pfn/->spanned_pages >>>>> resetting is moved into the if()/else if() branches, if the zone becomes >>>>> empty. However the 2nd resetting code block may cause misunderstanding. >>>>> >>>>> So take the resetting codes out of the conditional checking and handling >>>>> branches just as the old code does, the find_smallest_section_pfn()and >>>>> find_biggest_section_pfn() searching have done the the same thing as >>>>> the old for loop did, the logic is kept the same as the old code. This >>>>> can remove the possible confusion. >>>>> >>>>> Signed-off-by: Baoquan He >>>>> --- >>>>> mm/memory_hotplug.c | 14 ++++++-------- >>>>> 1 file changed, 6 insertions(+), 8 deletions(-) >>>>> >>>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >>>>> index 089b6c826a9e..475d0d68a32c 100644 >>>>> --- a/mm/memory_hotplug.c >>>>> +++ b/mm/memory_hotplug.c >>>>> @@ -398,7 +398,7 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone, >>>>> static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, >>>>> unsigned long end_pfn) >>>>> { >>>>> - unsigned long pfn; >>>>> + unsigned long pfn = zone->zone_start_pfn; >>>>> int nid = zone_to_nid(zone); >>>>> >>>>> zone_span_writelock(zone); >>>>> @@ -414,9 +414,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, >>>>> if (pfn) { >>>>> zone->spanned_pages = zone_end_pfn(zone) - pfn; >>>>> zone->zone_start_pfn = pfn; >>>>> - } else { >>>>> - zone->zone_start_pfn = 0; >>>>> - zone->spanned_pages = 0; >>>>> } >>>>> } else if (zone_end_pfn(zone) == end_pfn) { >>>>> /* >>>>> @@ -429,10 +426,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, >>>>> start_pfn); >>>>> if (pfn) >>>>> zone->spanned_pages = pfn - zone->zone_start_pfn + 1; >>>>> - else { >>>>> - zone->zone_start_pfn = 0; >>>>> - zone->spanned_pages = 0; >>>>> - } >>>>> + } >>>>> + >>>>> + if (!pfn) { >>>>> + zone->zone_start_pfn = 0; >>>>> + zone->spanned_pages = 0; >>>>> } >>>>> zone_span_writeunlock(zone); >>>>> } >>>>> >>>> >>>> So, what if your zone starts at pfn 0? Unlikely that we can actually >>>> offline that, but still it is more confusing than the old code IMHO. >>>> Then I prefer to drop the second else case as discussed instead. >>> >>> Hmm, pfn is initialized as zone->zone_start_pfn, does it matter? >>> The impossible empty zone won't go wrong if it really happen. >>> >> >> If you offline any memory block that belongs to the lowest zone >> (zone->zone_start_pfn == 0) but does not fall on a boundary (so that you >> can actually shrink), you would mark the whole zone offline. That's >> broken unless I am missing something. > > AFAIK, the page 0 is reserved. No valid zone can start at 0, only empty > zone is. Please correct me if I am wrong. At least on x86 it indeed is :) So if this holds true for all archs Acked-by: David Hildenbrand Thanks! -- Thanks, David / dhildenb