Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932623Ab2KNOwM (ORCPT ); Wed, 14 Nov 2012 09:52:12 -0500 Received: from mail-pa0-f46.google.com ([209.85.220.46]:61617 "EHLO mail-pa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752655Ab2KNOwK (ORCPT ); Wed, 14 Nov 2012 09:52:10 -0500 Message-ID: <50A3B013.4030207@gmail.com> Date: Wed, 14 Nov 2012 22:52:03 +0800 From: Jiang Liu User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121028 Thunderbird/16.0.2 MIME-Version: 1.0 To: Andrew Morton CC: Jiang Liu , Maciej Rutecki , Jianguo Wu , Chris Clayton , "Rafael J. Wysocki" , Mel Gorman , Minchan Kim , KAMEZAWA Hiroyuki , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Daniel Vetter Subject: Re: [PATCH] mm: fix a regression with HIGHMEM introduced by changeset 7f1290f2f2a4d References: <1352165517-9732-1-git-send-email-jiang.liu@huawei.com> <20121106124315.79deb2bc.akpm@linux-foundation.org> In-Reply-To: <20121106124315.79deb2bc.akpm@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4484 Lines: 105 On 11/07/2012 04:43 AM, Andrew Morton wrote: > On Tue, 6 Nov 2012 09:31:57 +0800 > Jiang Liu wrote: > >> Changeset 7f1290f2f2 tries to fix a issue when calculating >> zone->present_pages, but it causes a regression to 32bit systems with >> HIGHMEM. With that changeset, function reset_zone_present_pages() >> resets all zone->present_pages to zero, and fixup_zone_present_pages() >> is called to recalculate zone->present_pages when boot allocator frees >> core memory pages into buddy allocator. Because highmem pages are not >> freed by bootmem allocator, all highmem zones' present_pages becomes >> zero. >> >> Actually there's no need to recalculate present_pages for highmem zone >> because bootmem allocator never allocates pages from them. So fix the >> regression by skipping highmem in function reset_zone_present_pages() >> and fixup_zone_present_pages(). >> >> ... >> >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -6108,7 +6108,8 @@ void reset_zone_present_pages(void) >> for_each_node_state(nid, N_HIGH_MEMORY) { >> for (i = 0; i < MAX_NR_ZONES; i++) { >> z = NODE_DATA(nid)->node_zones + i; >> - z->present_pages = 0; >> + if (!is_highmem(z)) >> + z->present_pages = 0; >> } >> } >> } >> @@ -6123,10 +6124,11 @@ void fixup_zone_present_pages(int nid, unsigned long start_pfn, >> >> for (i = 0; i < MAX_NR_ZONES; i++) { >> z = NODE_DATA(nid)->node_zones + i; >> + if (is_highmem(z)) >> + continue; >> + >> zone_start_pfn = z->zone_start_pfn; >> zone_end_pfn = zone_start_pfn + z->spanned_pages; >> - >> - /* if the two regions intersect */ >> if (!(zone_start_pfn >= end_pfn || zone_end_pfn <= start_pfn)) >> z->present_pages += min(end_pfn, zone_end_pfn) - >> max(start_pfn, zone_start_pfn); > > This ... isn't very nice. It is embeds within > reset_zone_present_pages() and fixup_zone_present_pages() knowledge > about their caller's state. Or, more specifically, it is emebedding > knowledge about the overall state of the system when these functions > are called. > > I mean, a function called "reset_zone_present_pages" should reset > ->present_pages! > > The fact that fixup_zone_present_page() has multiple call sites makes > this all even more risky. And what are the interactions between this > and memory hotplug? > > Can we find a cleaner fix? > > Please tell us more about what's happening here. Is it the case that > reset_zone_present_pages() is being called *after* highmem has been > populated? If so, then fixup_zone_present_pages() should work > correctly for highmem? Or is it the case that highmem hasn't yet been > setup? IOW, what is the sequence of operations here? > > Is the problem that we're *missing* a call to > fixup_zone_present_pages(), perhaps? If we call > fixup_zone_present_pages() after highmem has been populated, > fixup_zone_present_pages() should correctly fill in the highmem zone's > ->present_pages? Hi Andrew, Sorry for the late response:( I have done more investigations according to your suggestions. Currently we have only called fixup_zone_present_pages() for memory freed by bootmem allocator and missed HIGHMEM pages. We could also call fixup_zone_present_pages() for HIGHMEM pages, but that will need to change arch specific code for x86, powerpc, sparc, microblaze, arm, mips, um and tile etc. Seems a little overhead. And sadly enough, I found the quick fix is still incomplete. The original patch still have another issue that, reset_zone_present_pages() is only called for IA64, so it will cause trouble for other arches which make use of "bootmem.c". Then I feel a little guilty and tried to find a cleaner solution without touching arch specific code. But things are more complex than my expectation and I'm still working on that. So how about totally reverting the changeset 7f1290f2f2a4d2c3f1b7ce8e87256e052ca23125 and I will post another version once I found a cleaner way? Thanks! Gerry > > > -- > 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/ > -- 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/