Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756029Ab3JRPFQ (ORCPT ); Fri, 18 Oct 2013 11:05:16 -0400 Received: from mail-we0-f180.google.com ([74.125.82.180]:34217 "EHLO mail-we0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755838Ab3JRPFO (ORCPT ); Fri, 18 Oct 2013 11:05:14 -0400 MIME-Version: 1.0 In-Reply-To: <00000141c7d66282-aa92b1f2-2a69-424b-9498-8e5367304d32-000000@email.amazonses.com> References: <1381913052-23875-1-git-send-email-iamjoonsoo.kim@lge.com> <1381913052-23875-14-git-send-email-iamjoonsoo.kim@lge.com> <00000141c7d66282-aa92b1f2-2a69-424b-9498-8e5367304d32-000000@email.amazonses.com> Date: Sat, 19 Oct 2013 00:05:12 +0900 Message-ID: Subject: Re: [PATCH v2 13/15] slab: use struct page for slab management From: JoonSoo Kim To: Christoph Lameter Cc: Joonsoo Kim , Pekka Enberg , Andrew Morton , David Rientjes , Linux Memory Management List , LKML , Wanpeng Li Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1757 Lines: 34 2013/10/18 Christoph Lameter : > On Wed, 16 Oct 2013, Joonsoo Kim wrote: > >> - * see PAGE_MAPPING_ANON below. >> - */ >> + union { >> + struct address_space *mapping; /* If low bit clear, points to >> + * inode address_space, or NULL. >> + * If page mapped as anonymous >> + * memory, low bit is set, and >> + * it points to anon_vma object: >> + * see PAGE_MAPPING_ANON below. >> + */ >> + void *s_mem; /* slab first object */ >> + }; > > The overloading of mapping has caused problems in the past since slab > pages are (or are they no longer?) used for DMA to disk. At that point the > I/O subsystem may be expecting a mapping in the page struct if this field > is not NULL. I search the history of struct page and find that the SLUB use mapping field in past (2007 year). At that time, you inserted VM_BUG_ON(PageSlab(page)) ('b5fab14') into page_mapping() function to find remaining use. Recently, I never hear that this is triggered and 6 years have passed since inserting VM_BUG_ON(), so I guess there is no problem to use it. If this argument is reasonable, please give me an ACK :) Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/