From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f41.google.com (mail-pb0-f41.google.com [209.85.160.41]) by kanga.kvack.org (Postfix) with ESMTP id 611816B0164 for ; Fri, 18 Oct 2013 11:05:17 -0400 (EDT) Received: by mail-pb0-f41.google.com with SMTP id rp16so3975324pbb.28 for ; Fri, 18 Oct 2013 08:05:17 -0700 (PDT) Received: from psmtp.com ([74.125.245.127]) by mx.google.com with SMTP id u7si1703224pau.194.2013.10.18.08.05.15 for ; Fri, 18 Oct 2013 08:05:16 -0700 (PDT) Received: by mail-wg0-f46.google.com with SMTP id m15so3834319wgh.1 for ; Fri, 18 Oct 2013 08:05:13 -0700 (PDT) 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 Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: Joonsoo Kim , Pekka Enberg , Andrew Morton , David Rientjes , Linux Memory Management List , LKML , Wanpeng Li 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, 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