From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [patch 00/14] remap_file_pages protection support From: Lee Schermerhorn In-Reply-To: <4456D5ED.2040202@yahoo.com.au> References: <20060430172953.409399000@zion.home.lan> <4456D5ED.2040202@yahoo.com.au> Content-Type: text/plain Date: Tue, 02 May 2006 13:16:46 -0400 Message-Id: <1146590207.5202.17.camel@localhost.localdomain> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: blaisorblade@yahoo.it, Andrew Morton , linux-kernel , Linux Memory Management List-ID: On Tue, 2006-05-02 at 13:45 +1000, Nick Piggin wrote: > blaisorblade@yahoo.it wrote: > > > The first idea is to use this for UML - it must create a lot of single page > > mappings, and managing them through separate VMAs is slow. > > I don't know about this. The patches add some complexity, I guess because > we now have vmas which cannot communicate the protectedness of the pages. > Still, nobody was too concerned about nonlinear mappings doing the same > for addressing. But this does seem to add more overhead to the common cases > in the VM :( > > Now I didn't follow the earlier discussions on this much, but let me try > making a few silly comments to get things going again (cc'ed linux-mm). > > I think I would rather this all just folded under VM_NONLINEAR rather than > having this extra MANYPROTS thing, no? (you're already doing that in one > direction). One way I've seen this done on other systems is to use something like a prio tree [e.g., see the shared policy support for shmem] for sub-vma protection ranges. Most vmas [I'm guessing here] will have only the original protections or will be reprotected in toto. So, one need only allocate/populate the protection tree when sub-vma protections are requested. Then, one can test protections via the vma, perhaps with access/check macros to hide the existence of the protection tree. Of course, adding a tree-like structure could introduce locking complications/overhead in some paths where we'd rather not [just guessing again]. Might be more overhead than just mucking with the ptes [for UML], but would keep the ptes in sync with the vma's view of "protectedness". Lee -- 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