Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752806AbbHEObS (ORCPT ); Wed, 5 Aug 2015 10:31:18 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:14467 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751971AbbHEObP (ORCPT ); Wed, 5 Aug 2015 10:31:15 -0400 X-IronPort-AV: E=Sophos;i="5.15,617,1432598400"; d="scan'208";a="291611433" Message-ID: <55C21DF3.2090201@citrix.com> Date: Wed, 5 Aug 2015 15:30:11 +0100 From: Julien Grall User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.7.0 MIME-Version: 1.0 To: David Vrabel , CC: , Boris Ostrovsky , , , Subject: Re: [Xen-devel] [PATCH v2 02/20] xen: Introduce a function to split a Linux page into Xen page References: <1436474552-31789-1-git-send-email-julien.grall@citrix.com> <1436474552-31789-3-git-send-email-julien.grall@citrix.com> <55B205FB.5080209@citrix.com> <55B20B56.7020605@citrix.com> <55B20F1F.60902@citrix.com> In-Reply-To: <55B20F1F.60902@citrix.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2379 Lines: 72 Hi David, On 24/07/15 11:10, David Vrabel wrote: > On 24/07/15 10:54, Julien Grall wrote: >> On 24/07/15 10:31, David Vrabel wrote: >>> On 09/07/15 21:42, Julien Grall wrote: >>>> The Xen interface is always using 4KB page. This means that a Linux page >>>> may be split across multiple Xen page when the page granularity is not >>>> the same. >>>> >>>> This helper will break down a Linux page into 4KB chunk and call the >>>> helper on each of them. >>> [...] >>>> --- a/include/xen/page.h >>>> +++ b/include/xen/page.h >>>> @@ -39,4 +39,24 @@ struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS]; >>>> >>>> extern unsigned long xen_released_pages; >>>> >>>> +typedef int (*xen_pfn_fn_t)(struct page *page, unsigned long pfn, void *data); >>>> + >>>> +/* Break down the page in 4KB granularity and call fn foreach xen pfn */ >>>> +static inline int xen_apply_to_page(struct page *page, xen_pfn_fn_t fn, >>>> + void *data) >>> >>> I think this should be outlined (unless you have measurements that >>> support making it inlined). >> >> I don't have any performance measurements. Although, when Linux is using >> 4KB page granularity, the loop in this helper will be dropped by the >> helper. The code would look like: >> >> unsigned long pfn = xen_page_to_pfn(page); >> >> ret = fn(page, fn, data); >> if (ret) >> return ret; >> >> The compiler could even inline the callback (fn). So it drops 2 >> functions call. > > Ok, keep it inlined. > >>> Also perhaps make it >>> >>> int xen_for_each_gfn(struct page *page, >>> xen_gfn_fn_t fn, void *data); >> >> gfn standing for Guest Frame Number right? > > Yes. This suggestion is just changing the name to make it more obvious > what it does. Thinking more about this suggestion. The callback (fn) is getting a 4K PFN in parameter and not a GFN. This is because the balloon code seems to require having a 4K PFN in hand in few places. For instance XENMEM_populate_physmap and HYPERVISOR_update_va_mapping. Although, I'm not sure to understand the difference between GMFN, and GPFN in the hypercall doc. Regards, -- Julien Grall -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/