From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 8 Nov 2005 13:53:25 +1100 From: David Gibson Subject: Re: [RFC 2/2] Hugetlb COW Message-ID: <20051108025325.GC10769@localhost.localdomain> References: <1131397841.25133.90.camel@localhost.localdomain> <1131399533.25133.104.camel@localhost.localdomain> <20051107233538.GH29402@holomorphy.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20051107233538.GH29402@holomorphy.com> Sender: owner-linux-mm@kvack.org Return-Path: To: William Lee Irwin III Cc: Adam Litke , linux-mm@kvack.org, linux-kernel@vger.kernel.org, hugh@veritas.com, rohit.seth@intel.com, "Chen, Kenneth W" , akpm@osdl.org List-ID: On Mon, Nov 07, 2005 at 03:35:38PM -0800, William Lee Irwin wrote: > On Mon, Nov 07, 2005 at 03:38:53PM -0600, Adam Litke wrote: > > [RFC] COW for hugepages > > (Patch originally from David Gibson ) > > This patch implements copy-on-write for hugepages, hence allowing > > MAP_PRIVATE mappings of hugetlbfs. > > This is chiefly useful for cases where we want to use hugepages > > "automatically" - that is to map hugepages without the knowledge of > > the code in the final application (either via kernel hooks, or with > > LD_PRELOAD). We can use various heuristics to determine when > > hugepages might be a good idea, but changing the semantics of > > anonymous memory from MAP_PRIVATE to MAP_SHARED without the app's > > knowledge is clearly wrong. > > I'll go check for architectures where page protections may be encoded > differently depending on the size of the translation, or whose code is > otherwise unprepared to cope with protection bits. > > If you've done such checking already, I'd be much obliged to hear of it > (in fact, I'd much prefer you to have done so). I can't see how the COW catch could be any more broken in this regard than we are already: make_huge_pte() in mm/hugetlb.c already assumes that pte_mkwrite() and pte_wrprotect() will work properly on hugepage PTEs. COW doesn't use anything more. -- 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