From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <47835FBE.8080406@de.ibm.com> Date: Tue, 08 Jan 2008 12:34:22 +0100 From: Carsten Otte Reply-To: carsteno@de.ibm.com MIME-Version: 1.0 Subject: Re: [rfc][patch 0/4] VM_MIXEDMAP patchset with s390 backend References: <20071214133817.GB28555@wotan.suse.de> <20071214134106.GC28555@wotan.suse.de> <476A73F0.4070704@de.ibm.com> <476A7D21.7070607@de.ibm.com> <20071221004556.GB31040@wotan.suse.de> <476B9000.2090707@de.ibm.com> <20071221102052.GB28484@wotan.suse.de> <476B96D6.2010302@de.ibm.com> <20071221104701.GE28484@wotan.suse.de> <1199784954.25114.27.camel@cotte.boeblingen.de.ibm.com> <20080108100803.GA24570@wotan.suse.de> In-Reply-To: <20080108100803.GA24570@wotan.suse.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: carsteno@de.ibm.com, Jared Hulbert , Linux Memory Management List , Martin Schwidefsky , Heiko Carstens List-ID: Nick Piggin wrote: > I'm just curious (or forgetful) as to why s390's pfn_valid does not walk > your memory segments? (That would allow the s390 proof of concept to be > basically a noop, and mixedmap_refcount_pfn will only be required when > we start using another pte bit. Our pfn_valid uses a hardware instruction, which does check if there is memory behind a pfn which we can access. And we'd like to use the very same memory segment for both regular memory hotplug where the memory ends up in ZONE_NORMAL (in this case the memory would be read+write, and not shared with other guests), and for backing xip file systems (in this case the memory would be read-only, and shared). And in both cases, our instruction does consider the pfn to be valid. Thus, pfn_valid is not the right indicator for us to check if we need refcounting or not. > I think using another bit in the pte for special mappings is reasonable. > As I posted in my earlier patch, we can also use it to simplify vm_normal_page, > and it facilitates a lock free get_user_pages. That patch looks very nice. I am going to define PTE_SPECIAL for s390 arch next... > Anyway, hmm... I guess we should probably get these patches into -mm and > then upstream soon. Any objections from anyone? Do you guys have performance / > stress testing for xip? I think it is mature enough to push upstream, I've booted a distro with /usr on it. But I really really want to exchange patch #4 with a pte-bit based one before pushing this. -- 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