From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx161.postini.com [74.125.245.161]) by kanga.kvack.org (Postfix) with SMTP id 695166B004D for ; Tue, 17 Apr 2012 09:03:22 -0400 (EDT) Received: from /spool/local by e06smtp13.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 17 Apr 2012 14:03:19 +0100 Received: from d06av02.portsmouth.uk.ibm.com (d06av02.portsmouth.uk.ibm.com [9.149.37.228]) by d06nrmr1707.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q3HD2kbO1216560 for ; Tue, 17 Apr 2012 14:02:46 +0100 Received: from d06av02.portsmouth.uk.ibm.com (loopback [127.0.0.1]) by d06av02.portsmouth.uk.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q3HD2iCd032472 for ; Tue, 17 Apr 2012 07:02:44 -0600 Date: Tue, 17 Apr 2012 15:02:37 +0200 From: Martin Schwidefsky Subject: Re: [RFC PATCH] s390: mm: rmap: Transfer storage key to struct page under the page lock Message-ID: <20120417150237.0abb8ec5@de.ibm.com> In-Reply-To: <20120417122925.GG2359@suse.de> References: <20120416141423.GD2359@suse.de> <20120416175040.0e33b37f@de.ibm.com> <20120417122925.GG2359@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Heiko Carstens , Hugh Dickins , Rik van Riel , Linux-MM , Linux-S390 , LKML On Tue, 17 Apr 2012 13:29:25 +0100 Mel Gorman wrote: > On Mon, Apr 16, 2012 at 05:50:40PM +0200, Martin Schwidefsky wrote: > > On Mon, 16 Apr 2012 15:14:23 +0100 > > Mel Gorman wrote: > > > > > This patch is horribly ugly and there has to be a better way of doing > > > it. I'm looking for suggestions on what s390 can do here that is not > > > painful or broken. > > > > > > However, s390 needs a better way of guarding against > > > PageSwapCache pages being removed from the radix tree while set_page_dirty() > > > is being called. The patch would be marginally better if in the PageSwapCache > > > case we simply tried to lock once and in the contended case just fail to > > > propogate the storage key. I lack familiarity with the s390 architecture > > > to be certain if this is safe or not. Suggestions on a better fix? > > > > One though that crossed my mind is that maybe a better approach would be > > to move the page_test_and_clear_dirty check out of page_remove_rmap. > > What we need to look out for are code sequences of the form: > > > > if (pte_dirty(pte)) > > set_page_dirty(page); > > ... > > page_remove_rmap(page); > > > > There are four of those as far as I can see: in try_to_unmap_one, > > try_to_unmap_cluster, zap_pte, and zap_pte_range. > > > > A valid implementation for s390 would be to test and clear the changed > > bit in the storage key for every of those pte_dirty() calls. > > > > if (pte_dirty(pte) || page_test_and_clear_dirty(page)) > > set_page_dirty(page); > > ... > > page_remove_rmap(page); /* w/o page_test_clear_dirty */ > > > > In the zap_pte_range() case at least, pte_dirty() is only being checked > for !PageAnon pages so if we took this approach we would miss > PageSwapCache pages. If we added the check then the same problem is hit > and we'd need additional logic there for s390 to drop the PTL, take the > page lock and retry the operation. It'd still be ugly :( Well if x86 can get away with ignoring PageSwapCache pages in zap_pte_range() pages then s390 should be able to get away with it as well, no ? -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org