From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 31 Oct 2006 22:05:40 +1100 From: 'David Gibson' Subject: Re: [RFC] reduce hugetlb_instantiation_mutex usage Message-ID: <20061031110540.GA14172@localhost.localdomain> References: <20061031031703.GA7220@localhost.localdomain> <000001c6fcab$8fe56320$5181030a@amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <000001c6fcab$8fe56320$5181030a@amr.corp.intel.com> Sender: owner-linux-mm@kvack.org Return-Path: To: "Chen, Kenneth W" Cc: g@ozlabs.org, Andrew Morton , 'Christoph Lameter' , Hugh Dickins , bill.irwin@oracle.com, Adam Litke , linux-mm@kvack.org List-ID: On Mon, Oct 30, 2006 at 09:15:20PM -0800, Chen, Kenneth W wrote: > David Gibson wrote on Monday, October 30, 2006 7:17 PM > > > I got side tracked on to the radix-tree stuff. The comments in > > > hugetlb_no_page() make me wonder whether we have a race issue on > > > private mapping: > > > > > > /* > > > * Use page lock to guard against racing truncation > > > * before we get page_table_lock. > > > */ > > > > > > Private mapping won't use radix tree during instantiation. What protects > > > racy truncate against fault in that scenario? Don't we have a bug here? > > > > Not at present, because the hugetlb_instantiation_mutex protects both > > fault paths. But with Andrew's patch as it stands, yes. As I said in > > a previous email. The libhugetlbfs testsuite now has a testcase for > > the MAP_PRIVATE as well as the MAP_SHARED version of the race. > > > That's not what I'm saying. I should've said I'm off topic and not talking > about parallel fault for private mapping. > > Instead, I'm asking how private mapping protect race between file truncation > and fault? For shared mapping, it is clear to me that we are using lock_page > to protect file truncate with fault. But I don't see that protection with > private mapping in current upstream kernel. Oh, ok. I can't see how it matters in the PRIVATE case, given that truncate() won't, and shouldn't, truncate privately mapped pages. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson -- 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