From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH v2 02/20] xen: Introduce a function to split a Linux page into Xen page Date: Wed, 5 Aug 2015 15:30:11 +0100 Message-ID: <55C21DF3.2090201__42644.9318453253$1438785162$gmane$org@citrix.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1ZMzj3-0006F9-1o for xen-devel@lists.xenproject.org; Wed, 05 Aug 2015 14:31:25 +0000 In-Reply-To: <55B20F1F.60902@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: David Vrabel , xen-devel@lists.xenproject.org Cc: Boris Ostrovsky , stefano.stabellini@eu.citrix.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, ian.campbell@citrix.com List-Id: xen-devel@lists.xenproject.org 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