From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yh0-f47.google.com (mail-yh0-f47.google.com [209.85.213.47]) by kanga.kvack.org (Postfix) with ESMTP id ADE486B0031 for ; Tue, 15 Jul 2014 20:02:47 -0400 (EDT) Received: by mail-yh0-f47.google.com with SMTP id f10so83800yha.20 for ; Tue, 15 Jul 2014 17:02:47 -0700 (PDT) Received: from g6t1525.atlanta.hp.com (g6t1525.atlanta.hp.com. [15.193.200.68]) by mx.google.com with ESMTPS id o29si27012177yha.63.2014.07.15.17.02.47 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Tue, 15 Jul 2014 17:02:47 -0700 (PDT) Message-ID: <1405468387.28702.53.camel@misato.fc.hp.com> Subject: Re: [RFC PATCH 3/11] x86, mm, pat: Change reserve_memtype() to handle WT type From: Toshi Kani Date: Tue, 15 Jul 2014 17:53:07 -0600 In-Reply-To: References: <1405452884-25688-1-git-send-email-toshi.kani@hp.com> <1405452884-25688-4-git-send-email-toshi.kani@hp.com> <1405465801.28702.34.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: Andy Lutomirski Cc: "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , Andrew Morton , Arnd Bergmann , Konrad Rzeszutek Wilk , plagnioj@jcrosoft.com, tomi.valkeinen@ti.com, "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Stefan Bader , Dave Airlie , Borislav Petkov On Tue, 2014-07-15 at 16:36 -0700, Andy Lutomirski wrote: > On Tue, Jul 15, 2014 at 4:10 PM, Toshi Kani wrote: > > On Tue, 2014-07-15 at 12:56 -0700, Andy Lutomirski wrote: > >> On Tue, Jul 15, 2014 at 12:34 PM, Toshi Kani wrote: > >> > This patch changes reserve_memtype() to handle the new WT type. > >> > When (!pat_enabled && new_type), it continues to set either WB > >> > or UC- to *new_type. When pat_enabled, it can reserve a given > >> > non-RAM range for WT. At this point, it may not reserve a RAM > >> > range for WT since reserve_ram_pages_type() uses the page flags > >> > limited to three memory types, WB, WC and UC. > >> > >> FWIW, last time I looked at this, it seemed like all the fancy > >> reserve_ram_pages stuff was unnecessary: shouldn't the RAM type be > >> easy to track in the direct map page tables? > > > > Are you referring the direct map page tables as the kernel page > > directory tables (pgd/pud/..)? > > > > I think it needs to be able to keep track of the memory type per a > > physical memory range, not per a translation, in order to prevent > > aliasing of the memory type. > > Actual RAM (the lowmem kind, which is all of it on x86_64) is mapped > linearly somewhere in kernel address space. The pagetables for that > mapping could be used as the canonical source of the memory type for > the ram range in question. > > This only works for lowmem, so maybe it's not a good idea to rely on it. Right. I think using struct page table for the RAM ranges is a good way for saving memory, but I wonder how often the RAM ranges are mapped other than WB... If not often, reserve_memtype() could simply call rbt_memtype_check_insert() for all ranges, including RAM. In this patch, I left using reserve_ram_pages_type() since I do not see much reason to use WT for RAM, either. 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