From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f53.google.com (mail-pa0-f53.google.com [209.85.220.53]) by kanga.kvack.org (Postfix) with ESMTP id 3CFDC6B0037 for ; Wed, 27 Aug 2014 19:05:18 -0400 (EDT) Received: by mail-pa0-f53.google.com with SMTP id fa1so104151pad.12 for ; Wed, 27 Aug 2014 16:05:17 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id gl10si3032856pbd.139.2014.08.27.16.05.17 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 27 Aug 2014 16:05:17 -0700 (PDT) Date: Wed, 27 Aug 2014 16:05:15 -0700 From: Andrew Morton Subject: Re: [PATCH 1/2] x86: Optimize resource lookups for ioremap Message-Id: <20140827160515.c59f1c191fde5f788a7c42f6@linux-foundation.org> In-Reply-To: <20140827225927.602319674@asylum.americas.sgi.com> References: <20140827225927.364537333@asylum.americas.sgi.com> <20140827225927.602319674@asylum.americas.sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mike Travis Cc: mingo@redhat.com, tglx@linutronix.de, hpa@zytor.com, msalter@redhat.com, dyoung@redhat.com, riel@redhat.com, peterz@infradead.org, mgorman@suse.de, linux-kernel@vger.kernel.org, x86@kernel.org, linux-mm@kvack.org, Alex Thorlton On Wed, 27 Aug 2014 17:59:28 -0500 Mike Travis wrote: > Since the ioremap operation is verifying that the specified address range > is NOT RAM, it will search the entire ioresource list if the condition > is true. To make matters worse, it does this one 4k page at a time. > For a 128M BAR region this is 32 passes to determine the entire region > does not contain any RAM addresses. > > This patch provides another resource lookup function, region_is_ram, > that searches for the entire region specified, verifying that it is > completely contained within the resource region. If it is found, then > it is checked to be RAM or not, within a single pass. > > The return result reflects if it was found or not (-1), and whether it is > RAM (1) or not (0). This allows the caller to fallback to the previous > page by page search if it was not found. > > ... > > --- linux.orig/kernel/resource.c > +++ linux/kernel/resource.c > @@ -494,6 +494,43 @@ int __weak page_is_ram(unsigned long pfn > } > EXPORT_SYMBOL_GPL(page_is_ram); > > +/* > + * Search for a resouce entry that fully contains the specified region. > + * If found, return 1 if it is RAM, 0 if not. > + * If not found, or region is not fully contained, return -1 > + * > + * Used by the ioremap functions to insure user not remapping RAM and is as > + * vast speed up over walking through the resource table page by page. > + */ > +int __weak region_is_ram(resource_size_t start, unsigned long size) > +{ > + struct resource *p; > + resource_size_t end = start + size - 1; > + int flags = IORESOURCE_MEM | IORESOURCE_BUSY; > + const char *name = "System RAM"; > + int ret = -1; > + > + read_lock(&resource_lock); > + for (p = iomem_resource.child; p ; p = p->sibling) { > + if (end < p->start) > + continue; > + > + if (p->start <= start && end <= p->end) { > + /* resource fully contains region */ > + if ((p->flags != flags) || strcmp(p->name, name)) > + ret = 0; > + else > + ret = 1; > + break; > + } > + if (p->end < start) > + break; /* not found */ > + } > + read_unlock(&resource_lock); > + return ret; > +} > +EXPORT_SYMBOL_GPL(region_is_ram); Exporting a __weak symbol is strange. I guess it works, but neither the __weak nor the export are actually needed? -- 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