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[66.63.167.143]) by mx.google.com with ESMTPS id e2si14380153ybe.268.2019.04.08.07.29.13 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 08 Apr 2019 07:29:13 -0700 (PDT) Received-SPF: pass (google.com: domain of james.bottomley@hansenpartnership.com designates 66.63.167.143 as permitted sender) client-ip=66.63.167.143; Authentication-Results: mx.google.com; dkim=fail header.i=@hansenpartnership.com header.s=20151216 header.b=ilwFB7fJ; dkim=fail header.i=@hansenpartnership.com header.s=20151216 header.b=GLNUu1vY; spf=pass (google.com: domain of james.bottomley@hansenpartnership.com designates 66.63.167.143 as permitted sender) smtp.mailfrom=James.Bottomley@hansenpartnership.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=hansenpartnership.com Received: from localhost (localhost [127.0.0.1]) by bedivere.hansenpartnership.com (Postfix) with ESMTP id 5958A8EE0ED; Mon, 8 Apr 2019 07:29:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=hansenpartnership.com; s=20151216; t=1554733752; bh=R2xhiC+0vMbSg7pyXTxfOfREJ8q93QOZwD4dtmqxljg=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=ilwFB7fJ1cbzFOf0lhsWoMxFI35bb2euibmlYKN0cxpzcwEUYt2YgMhpP7icNK+4X JkAQcPyRFWB6jaR4LO5qn5p8cHBh519VWuXd6+aSGznAPErnEFpJfWfNgQUW+vBtL8 ebxAmLJJyEGo/raFw3pF04m5c+D8owzM/hBhBE2c= Received: from bedivere.hansenpartnership.com ([127.0.0.1]) by localhost (bedivere.hansenpartnership.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id bADbGIfHE9TE; Mon, 8 Apr 2019 07:29:12 -0700 (PDT) Received: from [153.66.254.194] (unknown [50.35.68.20]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by bedivere.hansenpartnership.com (Postfix) with ESMTPSA id 80F3E8EE062; Mon, 8 Apr 2019 07:29:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=hansenpartnership.com; s=20151216; t=1554733751; bh=R2xhiC+0vMbSg7pyXTxfOfREJ8q93QOZwD4dtmqxljg=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=GLNUu1vYWD0x6NFM0uqCmwhz6PZzlLG7BZZqdWvMjwsNnixiLPttT06aQEa8KPU7x owAuI+OKkBHyI+lc6yGODSnZ5PLrq/QXDry2XXSaYf9qHi3OHu677NuE27baySRIHg 4WrQ7Rf5ffDnXRDCNt+tyLUbVpEMigHNVThrQlOI= Message-ID: <1554733749.3137.6.camel@HansenPartnership.com> Subject: Re: Memory management broken by "mm: reclaim small amounts of memory when an external fragmentation event occurs" From: James Bottomley To: Mel Gorman , Mikulas Patocka Cc: Andrew Morton , Helge Deller , John David Anglin , linux-parisc@vger.kernel.org, linux-mm@kvack.org, Vlastimil Babka , Andrea Arcangeli , Zi Yan Date: Mon, 08 Apr 2019 07:29:09 -0700 In-Reply-To: <20190408095224.GA18914@techsingularity.net> References: <20190408095224.GA18914@techsingularity.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.26.6 Mime-Version: 1.0 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 Mon, 2019-04-08 at 10:52 +0100, Mel Gorman wrote: > First, if pa-risc is !NUMA then why are separate local ranges > represented as separate nodes? Is it because of DISCONTIGMEM or > something else? DISCONTIGMEM is before my time so I'm not familiar > with it and I consider it "essentially dead" but the arch init code > seems to setup pgdats for each physical contiguous range so it's a > possibility. The most likely explanation is pa-risc does not have > hardware with addressing limitations smaller than the CPUs physical > address limits and it's possible to have more ranges than available > zones but clarification would be nice. Let me try, since I remember the ancient history. In the early days, there had to be a single mem_map array covering all of physical memory. Some pa-risc systems had huge gaps in the physical memory; I think one gap was somewhere around 1GB, so this lead us to wasting huge amounts of space in mem_map on non-existent memory. What CONFIG_DISCONTIGMEM did was allow you to represent this discontinuity on a non-NUMA system using numa nodes, so we effectively got one node per discontiguous range. It's hacky, but it worked. I thought we finally got converted to sparsemem by the NUMA people, but I can't find the commit. James