From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 210CAC4CEC5 for ; Thu, 12 Sep 2019 15:42:20 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E9CB920678 for ; Thu, 12 Sep 2019 15:42:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="U62vQctI" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E9CB920678 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Date:To:From:Subject:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=2JmaB93bRUodmfJvjlm4PRxHmDNeSt+xzlLU9BNkZi8=; b=U62vQctIXrhB/M oizx7Zf2yTt5sUTaq/UjQUV1vi16GHB5eAIHovixoGcWVwuxU+hDsGuwy41csgB/uG7rKDo8maxKY nAnSJAVf9twCs6i4lIleSCx0Tt4UDNdjrPcsV0ThgDY3ji3OVy0eWFbfpmk0MTYbDVN2vFT8a+Vcf 3d30SF0xXqSTBtRMnnNWqQxkQP+xY+7t74VM3XLLz8c8C6hf2U7QOQxSKMHA17go7n5YjluDAigY9 ZL5MjDdsQPFCvfI5+iXagkAzYdWv+oe6Mo0muQgKuny0WDcjEnsooTU0XzDv9sSGsq0YuwjC82qoA Xzu6nj6wPHh+bfrfkM3w==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.2 #3 (Red Hat Linux)) id 1i8REe-00054Z-9v; Thu, 12 Sep 2019 15:42:16 +0000 Received: from mga14.intel.com ([192.55.52.115]) by bombadil.infradead.org with esmtps (Exim 4.92.2 #3 (Red Hat Linux)) id 1i8REZ-00053r-Uy for linux-arm-kernel@lists.infradead.org; Thu, 12 Sep 2019 15:42:13 +0000 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga103.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Sep 2019 08:42:09 -0700 X-IronPort-AV: E=Sophos;i="5.64,492,1559545200"; d="scan'208";a="197265089" Received: from ahduyck-desk1.jf.intel.com ([10.7.198.76]) by orsmga002-auth.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Sep 2019 08:42:08 -0700 Message-ID: Subject: Re: [PATCH v9 0/8] stg mail -e --version=v9 \ From: Alexander Duyck To: Michal Hocko , Alexander Duyck Date: Thu, 12 Sep 2019 08:42:08 -0700 In-Reply-To: <20190912091925.GM4023@dhcp22.suse.cz> References: <20190907172225.10910.34302.stgit@localhost.localdomain> <20190910124209.GY2063@dhcp22.suse.cz> <20190910144713.GF2063@dhcp22.suse.cz> <20190910175213.GD4023@dhcp22.suse.cz> <1d7de9f9f4074f67c567dbb4cc1497503d739e30.camel@linux.intel.com> <20190911113619.GP4023@dhcp22.suse.cz> <20190912091925.GM4023@dhcp22.suse.cz> User-Agent: Evolution 3.30.5 (3.30.5-1.fc29) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190912_084212_002977_8AADAAF5 X-CRM114-Status: GOOD ( 28.05 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Yang Zhang , Pankaj Gupta , kvm list , David Hildenbrand , Catalin Marinas , lcapitulino@redhat.com, linux-mm , will@kernel.org, Andrea Arcangeli , virtio-dev@lists.oasis-open.org, "Michael S. Tsirkin" , Matthew Wilcox , "Wang, Wei W" , Mel Gorman , ying.huang@intel.com, Rik van Riel , Konrad Rzeszutek Wilk , Vlastimil Babka , Dan Williams , linux-arm-kernel@lists.infradead.org, Oscar Salvador , Nitesh Narayan Lal , Dave Hansen , LKML , Paolo Bonzini , Andrew Morton , Fengguang Wu , "Kirill A. Shutemov" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, 2019-09-12 at 11:19 +0200, Michal Hocko wrote: > On Wed 11-09-19 08:12:03, Alexander Duyck wrote: > > On Wed, Sep 11, 2019 at 4:36 AM Michal Hocko wrote: > > > On Tue 10-09-19 14:23:40, Alexander Duyck wrote: > > > [...] > > > > We don't put any limitations on the allocator other then that it needs to > > > > clean up the metadata on allocation, and that it cannot allocate a page > > > > that is in the process of being reported since we pulled it from the > > > > free_list. If the page is a "Reported" page then it decrements the > > > > reported_pages count for the free_area and makes sure the page doesn't > > > > exist in the "Boundary" array pointer value, if it does it moves the > > > > "Boundary" since it is pulling the page. > > > > > > This is still a non-trivial limitation on the page allocation from an > > > external code IMHO. I cannot give any explicit reason why an ordering on > > > the free list might matter (well except for page shuffling which uses it > > > to make physical memory pattern allocation more random) but the > > > architecture seems hacky and dubious to be honest. It shoulds like the > > > whole interface has been developed around a very particular and single > > > purpose optimization. > > > > How is this any different then the code that moves a page that will > > likely be merged to the tail though? > > I guess you are referring to the page shuffling. If that is the case > then this is an integral part of the allocator for a reason and it is > very well obvious in the code including the consequences. I do not > really like an idea of hiding similar constrains behind a generic > looking feature which is completely detached from the allocator and so > any future change of the allocator might subtly break it. > > > In our case the "Reported" page is likely going to be much more > > expensive to allocate and use then a standard page because it will be > > faulted back in. In such a case wouldn't it make sense for us to want > > to keep the pages that don't require faults ahead of those pages in > > the free_list so that they are more likely to be allocated? > > OK, I was suspecting this would pop out. And this is exactly why I > didn't like an idea of an external code imposing a non obvious constrains > to the allocator. You simply cannot count with any ordering with the > page allocator. We used to distinguish cache hot/cold pages in the past > and pushed pages to the specific end of the free list but that has been > removed. There are other potential changes like that possible. Shuffling > is a good recent example. > > Anyway I am not a maintainer of this code. I would really like to hear > opinions from Mel and Vlastimil here (now CCed - the thread starts > http://lkml.kernel.org/r/20190907172225.10910.34302.stgit@localhost.localdomain. One alternative I could do if we are wanting to make things more obvious would be to add yet another add_to_free_list_XXX function that would be used specifically for reported pages. The only real requirement I have is that we have to insert reported pages such that we generate a continuous block without interleaving non-reported pages in between. So as long as reported pages are always inserted at the boundary/iterator when we are actively reporting on a section then I can guarantee the list won't have gaps formed. Also as far as the concerns about this being an external user, one thing I can do is break up the headers a bit and define an internal header in mm/ that defines all the items used by the page allocator, and another in include/linux/ that defines what is used by devices when receiving the notifications. It would then help to reduce the likelihood of an outside entity messing with the page allocator too much. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel