From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756495AbbCRU0x (ORCPT ); Wed, 18 Mar 2015 16:26:53 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:38038 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754748AbbCRU0v (ORCPT ); Wed, 18 Mar 2015 16:26:51 -0400 Date: Wed, 18 Mar 2015 13:26:50 -0700 From: Andrew Morton To: Dan Williams Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, axboe@kernel.dk, riel@redhat.com, linux-nvdimm@ml01.01.org, Dave Hansen , linux-raid@vger.kernel.org, mgorman@suse.de, hch@infradead.org, linux-fsdevel@vger.kernel.org, Matthew Wilcox Subject: Re: [RFC PATCH 0/7] evacuate struct page from the block layer Message-Id: <20150318132650.3336261c58829f49a9af8675@linux-foundation.org> In-Reply-To: <20150316201640.33102.33761.stgit@dwillia2-desk3.amr.corp.intel.com> References: <20150316201640.33102.33761.stgit@dwillia2-desk3.amr.corp.intel.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 16 Mar 2015 16:25:25 -0400 Dan Williams wrote: > Avoid the impending disaster of requiring struct page coverage for what > is expected to be ever increasing capacities of persistent memory. In > conversations with Rik van Riel, Mel Gorman, and Jens Axboe at the > recently concluded Linux Storage Summit it became clear that struct page > is not required in many places, it was simply convenient to re-use. > > Introduce helpers and infrastructure to remove struct page usage where > it is not necessary. One use case for these changes is to implement a > write-back-cache in persistent memory for software-RAID. Another use > case for the scatterlist changes is RDMA to a pfn-range. Those use-cases sound very thin. If that's all we have then I'd say "find another way of implementing those things without creating pageframes for persistent memory". IOW, please tell us much much much more about the value of this change.