From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f70.google.com (mail-it0-f70.google.com [209.85.214.70]) by kanga.kvack.org (Postfix) with ESMTP id 10DB86B0003 for ; Wed, 31 Jan 2018 13:25:00 -0500 (EST) Received: by mail-it0-f70.google.com with SMTP id k19so469207ita.8 for ; Wed, 31 Jan 2018 10:25:00 -0800 (PST) Received: from userp2130.oracle.com (userp2130.oracle.com. [156.151.31.86]) by mx.google.com with ESMTPS id a2si262294itg.59.2018.01.31.10.24.58 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 31 Jan 2018 10:24:58 -0800 (PST) Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.22/8.16.0.22) with SMTP id w0VIMUBf136182 for ; Wed, 31 Jan 2018 18:24:57 GMT Received: from userv0021.oracle.com (userv0021.oracle.com [156.151.31.71]) by userp2130.oracle.com with ESMTP id 2fujpm83qx-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK) for ; Wed, 31 Jan 2018 18:24:57 +0000 Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by userv0021.oracle.com (8.14.4/8.14.4) with ESMTP id w0VIOuIc010795 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL) for ; Wed, 31 Jan 2018 18:24:56 GMT Received: from abhmp0006.oracle.com (abhmp0006.oracle.com [141.146.116.12]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id w0VIOuS0005564 for ; Wed, 31 Jan 2018 18:24:56 GMT Received: by mail-oi0-f52.google.com with SMTP id l8so11301689oig.0 for ; Wed, 31 Jan 2018 10:24:56 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <9ED437F7446DF74B826BE56C7BB1B89E95C1459F@G05USEXSUYA02.g05.fujitsu.local> References: <20171115141329.ieoqvyoavmv6gnea@techsingularity.net> <20171115142816.zxdgkad3ch2bih6d@dhcp22.suse.cz> <20171115144314.xwdi2sbcn6m6lqdo@techsingularity.net> <20171115145716.w34jaez5ljb3fssn@dhcp22.suse.cz> <06a33f82-7f83-7721-50ec-87bf1370c3d4@gmail.com> <20171116085433.qmz4w3y3ra42j2ih@dhcp22.suse.cz> <20171116100633.moui6zu33ctzpjsf@techsingularity.net> <20171117213206.eekbiiexygig7466@techsingularity.net> <20171206105000.4aefxr3uzvutulvb@techsingularity.net> <9ED437F7446DF74B826BE56C7BB1B89E95C1459F@G05USEXSUYA02.g05.fujitsu.local> From: Pavel Tatashin Date: Wed, 31 Jan 2018 13:24:55 -0500 Message-ID: Subject: Re: [PATCH] mm, meminit: Serially initialise deferred memory if trace_buf_size is specified Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: "Koki.Sanagi@us.fujitsu.com" Cc: Mel Gorman , Michal Hocko , YASUAKI ISHIMATSU , Andrew Morton , Linux Memory Management List , "linux-kernel@vger.kernel.org" , Steve Sistare , "msys.mizuma@gmail.com" Hi Koki, Yes, the patch is here: https://lkml.org/lkml/2018/1/12/600 It has not been reviewed yet. Pavel On Wed, Jan 31, 2018 at 12:28 PM, Koki.Sanagi@us.fujitsu.com wrote: > Pavel, > > I assume you are working on the fix. > Do you have any progress ? > > Koki > >>>-----Original Message----- >>>From: Mel Gorman [mailto:mgorman@techsingularity.net] >>>Sent: Wednesday, December 06, 2017 5:50 AM >>>To: Pavel Tatashin >>>Cc: Michal Hocko ; YASUAKI ISHIMATSU >>>; Andrew Morton ; >>>Linux Memory Management List ; linux- >>>kernel@vger.kernel.org; Sanagi, Koki ; Steve >>>Sistare >>>Subject: Re: [PATCH] mm, meminit: Serially initialise deferred memory if >>>trace_buf_size is specified >>> >>>On Wed, Nov 29, 2017 at 10:41:59PM -0500, Pavel Tatashin wrote: >>>> Hi Mel, >>>> >>>> Thank you very much for your feedback, my replies below: >>>> >>>> > A lack of involvement from admins is indeed desirable. For example, >>>> > while I might concede on using a disable-everything-switch, I would >>>> > not be happy to introduce a switch that specified how much memory >>>> > per node to initialise. >>>> > >>>> > For the forth approach, I really would be only thinking of a blunt >>>> > "initialise everything instead of going OOM". I was wary of making >>>> > things too complicated and I worried about some side-effects I'll cover later. >>>> >>>> I see, I misunderstood your suggestion. Switching to serial >>>> initialization when OOM works, however, boot time becomes >>>> unpredictable, with some configurations boot is fast with others it is >>>> slow. All of that depends on whether predictions in >>>> reset_deferred_meminit() were good or not which is not easy to debug >>>> for users. Also, overtime predictions in reset_deferred_meminit() can >>>> become very off, and I do not think that we want to continuously >>>> adjust this function. >>>> >>> >>>You could increase the probabilty of a report by doing a WARN_ON_ONCE if the >>>serialised meminit is used. >>> >>>> >> With this approach we could always init a very small amount of >>>> >> struct pages, and allow the rest to be initialized on demand as >>>> >> boot requires until deferred struct pages are initialized. Since, >>>> >> having deferred pages feature assumes that the machine is large, >>>> >> there is no drawback of having some extra byte of dead code, >>>> >> especially that all the checks can be permanently switched of via >>>> >> static branches once deferred init is complete. >>>> >> >>>> > >>>> > This is where I fear there may be dragons. If we minimse the number >>>> > of struct pages and initialise serially as necessary, there is a >>>> > danger that we'll allocate remote memory in cases where local memory >>>> > would have done because a remote node had enough memory. >>>> >>>> True, but is not what we have now has the same issue as well? If one >>>> node is gets out of memory we start using memory from another node, >>>> before deferred pages are initialized? >>>> >>> >>>It's possible but I'm not aware of it happening currently. >>> >>>> To offset that risk, it would be >>>> > necessary at boot-time to force allocations from local node where >>>> > possible and initialise more memory as necessary. That starts >>>> > getting complicated because we'd need to adjust gfp-flags in the >>>> > fast path with init-and-retry logic in the slow path and that could >>>> > be a constant penalty. We could offset that in the fast path by >>>> > using static branches >>>> >>>> I will try to implement this, and see how complicated the patch will >>>> be, if it gets too complicated for the problem I am trying to solve we >>>> can return to one of your suggestions. >>>> >>>> I was thinking to do something like this: >>>> >>>> Start with every small amount of initialized pages in every node. >>>> If allocation fails, initialize enough struct pages to cover this >>>> particular allocation with struct pages rounded up to section size but >>>> in every single node. >>>> >>> >>>Ok, just make sure it's all in the slow paths of the allocator when the alternative >>>is to fail the allocation. >>> >>>> > but it's getting more and >>>> > more complex for what is a minor optimisation -- shorter boot times >>>> > on large machines where userspace itself could take a *long* time to >>>> > get up and running (think database reading in 1TB of data from disk as it >>>warms up). >>>> >>>> On M6-32 with 32T [1] of memory it saves over 4 minutes of boot time, >>>> and this is on SPARC with 8K pages, on x86 it would be around of 8 >>>> minutes because of twice as many pages. This feature improves >>>> availability for larger machines quite a bit. Overtime, systems are >>>> growing, so I expect this feature to become a default configuration in >>>> the next several years on server configs. >>>> >>> >>>Ok, when developing the series originally, I had no machine even close to 32T of >>>memory. >>> >>>-- >>>Mel Gorman >>>SUSE Labs > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org