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Wed, 6 Nov 2019 23:33:35 +0000 (UTC) Received: from [10.36.116.42] (ovpn-116-42.ams2.redhat.com [10.36.116.42]) by smtp.corp.redhat.com (Postfix) with ESMTP id 03A22600D3; Wed, 6 Nov 2019 23:33:23 +0000 (UTC) Subject: Re: + mm-introduce-reported-pages.patch added to -mm tree To: Alexander Duyck , Michal Hocko Cc: akpm@linux-foundation.org, aarcange@redhat.com, dan.j.williams@intel.com, dave.hansen@intel.com, konrad.wilk@oracle.com, lcapitulino@redhat.com, mgorman@techsingularity.net, mm-commits@vger.kernel.org, mst@redhat.com, osalvador@suse.de, pagupta@redhat.com, pbonzini@redhat.com, riel@surriel.com, vbabka@suse.cz, wei.w.wang@intel.com, willy@infradead.org, yang.zhang.wz@gmail.com, linux-mm@kvack.org References: <20191106121605.GH8314@dhcp22.suse.cz> <20191106165416.GO8314@dhcp22.suse.cz> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Thu, 7 Nov 2019 00:33:23 +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: Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-MC-Unique: cn7-xLknMkiH4qEwGt3HuQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable 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 06.11.19 18:48, Alexander Duyck wrote: > On Wed, 2019-11-06 at 17:54 +0100, Michal Hocko wrote: >> On Wed 06-11-19 08:35:43, Alexander Duyck wrote: >>> On Wed, 2019-11-06 at 15:09 +0100, David Hildenbrand wrote: >>>>> Am 06.11.2019 um 13:16 schrieb Michal Hocko : >>>>> >>>>> =EF=BB=BFI didn't have time to read through newer versions of this pa= tch series >>>>> but I remember there were concerns about this functionality being pul= led >>>>> into the page allocator previously both by me and Mel [1][2]. Have th= ose been >>>>> addressed? I do not see an ack from Mel or any other MM people. Is th= ere >>>>> really a consensus that we want something like that living in the >>>>> allocator? >>>> >>>> I don=E2=80=98t think there is. The discussion is still ongoing (altho= ugh quiet, >>>> Nitesh is working on a new version AFAIK). I think we should not rush >>>> this. >>> >>> How much time is needed to get a review? I waited 2 weeks since posting >>> v12 and the only comments I got on the code were from Andrew. Most of t= his >>> hasn't changed much since v10 and that was posted back in mid September= . I >>> have been down to making small tweaks here and there and haven't had an= y >>> real critiques on the approach since Mel had the comments about conflic= ts >>> with compaction which I addressed by allowing compaction to punt the >>> reporter out so that it could split and splice the lists as it walked >>> through them. >> >> Well, people are busy and MM community is not a large one. I cannot >> really help you much other than keep poking those people and give >> reasonable arguments so they decide to ack your patch. >=20 > I get that. But v10 was posted in mid September. Back then we had a > discussion about addressing what Mel had mentioned and I had mentioned > then that I had addressed it by allowing compaction to essentially reset > the reporter to get it out of the list so compaction could do this split > and splice tumbling logic. >=20 >> I definitely do not intent to nack this work, I just have maintainabilit= y >> concerns and considering there is an alternative approach that does not >> require to touch page allocator internals and which we need to compare >> against then I do not really think there is any need to push something >> in right away. Or is there any pressing reason to have this merged right >> now? >=20 > The alternative approach doesn't touch the page allocator, however it > still has essentially the same changes to __free_one_page. I suspect the Nitesh is working on Michals suggestion to use page isolation instead=20 AFAIK - which avoids this. > performance issue seen is mostly due to the fact that because it doesn't > touch the page allocator it is taking the zone lock and probing the page > for each set bit to see if the page is still free. As such the performanc= e > regression seen gets worse the lower the order used for reporting. >=20 > Also I suspect Nitesh's patches are also in need of further review. I hav= e > provided feedback however my focus ended up being on more the kernel > panics and 30% performance regression rather than debating architecture. Please don't take this personally, but I really dislike you taking about=20 Niteshs RFCs (!) and pushing for your approach (although it was you that=20 was late to the party!) in that way. If there are problems then please=20 collaborate and fix instead of using the same wrong arguments over and=20 over again. a) hotplug/sparse zones: I explained a couple of times why we can ignore=20 that. There was never a reply from you, yet you keep coming up with=20 that. I don't enjoy talking to a wall. b) Locking optimizations: Come on, these are premature optimizations and=20 nothing to dictate your design. *nobody* but you cares about that in an=20 initial approach we get upstream. We can always optimize that. c) Kernel panics: Come on, we are talking about complicated RFCs here=20 with moving design decisions. We want do discuss *design* and=20 *architecture* here, not *implementation details*. d) Performance: We want to see a design that fits into the whole=20 architecture cleanly, is maintainable, and provides a benefit. Of=20 course, performance is relevant, but it certainly should not dictate our=20 design of a *virtualization specific optimization feature*. Performance=20 is not everything, otherwise please feel free and rewrite the kernel in=20 ASM and claim it is better because it is faster. Again, I do value your review and feedback, but I absolutely do not=20 enjoy the way you are trying to push your series here, sorry. Yes, if we end up finding out that there is real value in your approach,=20 nothing speaks against considering it. But please don't try to hurry and=20 push your series in that way. Please give everybody to time to evaluate. --=20 Thanks, David / dhildenb