From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f178.google.com (mail-ob0-f178.google.com [209.85.214.178]) by kanga.kvack.org (Postfix) with ESMTP id 5D70F6B0085 for ; Fri, 29 May 2015 14:51:55 -0400 (EDT) Received: by obcnx10 with SMTP id nx10so58826669obc.2 for ; Fri, 29 May 2015 11:51:55 -0700 (PDT) Received: from g4t3427.houston.hp.com (g4t3427.houston.hp.com. [15.201.208.55]) by mx.google.com with ESMTPS id h5si4073653oer.59.2015.05.29.11.51.54 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 29 May 2015 11:51:54 -0700 (PDT) Message-ID: <1432924340.23540.78.camel@misato.fc.hp.com> Subject: Re: [PATCH v10 12/12] drivers/block/pmem: Map NVDIMM with ioremap_wt() From: Toshi Kani Date: Fri, 29 May 2015 12:32:20 -0600 In-Reply-To: References: <1432739944-22633-1-git-send-email-toshi.kani@hp.com> <1432739944-22633-13-git-send-email-toshi.kani@hp.com> <20150529091129.GC31435@pd.tnic> <1432911782.23540.55.camel@misato.fc.hp.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dan Williams Cc: Borislav Petkov , Ross Zwisler , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , Andrew Morton , Arnd Bergmann , linux-mm@kvack.org, "linux-kernel@vger.kernel.org" , X86 ML , "linux-nvdimm@lists.01.org" , jgross@suse.com, Stefan Bader , Andy Lutomirski , hmh@hmh.eng.br, yigal@plexistor.com, Konrad Rzeszutek Wilk , "Elliott, Robert (Server Storage)" , mcgrof@suse.com, Christoph Hellwig , Matthew Wilcox On Fri, 2015-05-29 at 11:19 -0700, Dan Williams wrote: > On Fri, May 29, 2015 at 8:03 AM, Toshi Kani wrote: > > On Fri, 2015-05-29 at 07:43 -0700, Dan Williams wrote: > >> On Fri, May 29, 2015 at 2:11 AM, Borislav Petkov wrote: > >> > On Wed, May 27, 2015 at 09:19:04AM -0600, Toshi Kani wrote: > >> >> The pmem driver maps NVDIMM with ioremap_nocache() as we cannot : > >> >> - pmem->virt_addr = ioremap_nocache(pmem->phys_addr, pmem->size); > >> >> + pmem->virt_addr = ioremap_wt(pmem->phys_addr, pmem->size); > >> >> if (!pmem->virt_addr) > >> >> goto out_release_region; > >> > > >> > Dan, Ross, what about this one? > >> > > >> > ACK to pick it up as a temporary solution? > >> > >> I see that is_new_memtype_allowed() is updated to disallow some > >> combinations, but the manual seems to imply any mixing of memory types > >> is unsupported. Which worries me even in the current code where we > >> have uncached mappings in the driver, and potentially cached DAX > >> mappings handed out to userspace. > > > > is_new_memtype_allowed() is not to allow some combinations of mixing of > > memory types. When it is allowed, the requested type of ioremap_xxx() > > is changed to match with the existing map type, so that mixing of memory > > types does not happen. > > Yes, but now if the caller was expecting one memory type and gets > another one that is something I think the driver would want to know. > At a minimum I don't think we want to get emails about pmem driver > performance problems when someone's platform is silently degrading WB > to UC for example. The pmem driver creates an ioremap map to an NVDIMM range first. So, there will be no conflict at this point, unless there is a conflicting driver claiming the same NVDIMM range. DAX then uses the pmem driver (or other byte-addressable driver) to mount a file system and creates a separate user-space mapping for mmap(). So, a (silent) map-type conflict will happen at this point, which may not be protected by the ioremap itself. > > DAX uses vm_insert_mixed(), which does not even check the existing map > > type to the physical address. > > Right, I think that's a problem... > > >> A general quibble separate from this patch is that we don't have a way > >> of knowing if ioremap() will reject or change our requested memory > >> type. Shouldn't the driver be explicitly requesting a known valid > >> type in advance? > > > > I agree we need a solution here. > > > >> Lastly we now have the PMEM API patches from Ross out for review where > >> he is assuming cached mappings with non-temporal writes: > >> https://lists.01.org/pipermail/linux-nvdimm/2015-May/000929.html. > >> This gives us WC semantics on writes which I believe has the nice > >> property of reducing the number of write transactions to memory. > >> Also, the numbers in the paper seem to be assuming DAX operation, but > >> this ioremap_wt() is in the driver and typically behind a file system. > >> Are the numbers relevant to that usage mode? > > > > I have not looked into the Ross's changes yet, but they do not seem to > > replace the use of ioremap_nocache(). If his changes can use WB type > > reliably, yes, we do not need a temporary solution of using ioremap_wt() > > in this driver. > > Hmm, yes you're right, it seems those patches did not change the > implementation to use ioremap_cache()... which happens to not be > implemented on all architectures. I'll take a look. Thanks, -Toshi -- 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