From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f48.google.com (mail-pa0-f48.google.com [209.85.220.48]) by kanga.kvack.org (Postfix) with ESMTP id 6F73D6B0069 for ; Thu, 23 Oct 2014 15:18:41 -0400 (EDT) Received: by mail-pa0-f48.google.com with SMTP id ey11so1633541pad.7 for ; Thu, 23 Oct 2014 12:18:41 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id qv8si2364363pbb.75.2014.10.23.12.18.40 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 23 Oct 2014 12:18:40 -0700 (PDT) Date: Thu, 23 Oct 2014 12:18:40 -0700 From: Andrew Morton Subject: Re: [RFC] mm: memblock: change default cnt for regions from 1 to 0 Message-Id: <20141023121840.f88439912f23a3c2a01eb54f@linux-foundation.org> In-Reply-To: <1414083413-61756-1-git-send-email-Zubair.Kakakhel@imgtec.com> References: <1414083413-61756-1-git-send-email-Zubair.Kakakhel@imgtec.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: Zubair Lutfullah Kakakhel Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Tejun Heo , Tang Chen , Yinghai Lu (cc's added) On Thu, 23 Oct 2014 17:56:53 +0100 Zubair Lutfullah Kakakhel wrote: > The default region counts are set to 1 with a comment saying empty > dummy entry. > > If this is a dummy entry, should this be changed to 0? > > We have faced this in mips/kernel/setup.c arch_mem_init. > > cma uses memblock. But even with cma disabled. > The for_each_memblock(reserved, reg) goes inside the loop. > Even without any reserved regions. > > Traced it to the following, when the macro > for_each_memblock(memblock_type, region) is used. > > It expands to add the cnt variable. > > for (region = memblock.memblock_type.regions; \ > region < (memblock.memblock_type.regions + memblock.memblock_type.cnt); \ > region++) > > In the corner case, that there are no reserved regions. > Due to the default 1 value of cnt. > The loop under for_each_memblock still runs once. > > Even when there is no reserved region. > > Is this by design? or unintentional? > It might be that this loop runs an extra time every instance out there? > --- > mm/memblock.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/memblock.c b/mm/memblock.c > index 6d2f219..b91301c 100644 > --- a/mm/memblock.c > +++ b/mm/memblock.c > @@ -33,16 +33,16 @@ static struct memblock_region memblock_physmem_init_regions[INIT_PHYSMEM_REGIONS > > struct memblock memblock __initdata_memblock = { > .memory.regions = memblock_memory_init_regions, > - .memory.cnt = 1, /* empty dummy entry */ > + .memory.cnt = 0, /* empty dummy entry */ > .memory.max = INIT_MEMBLOCK_REGIONS, > > .reserved.regions = memblock_reserved_init_regions, > - .reserved.cnt = 1, /* empty dummy entry */ > + .reserved.cnt = 0, /* empty dummy entry */ > .reserved.max = INIT_MEMBLOCK_REGIONS, > > #ifdef CONFIG_HAVE_MEMBLOCK_PHYS_MAP > .physmem.regions = memblock_physmem_init_regions, > - .physmem.cnt = 1, /* empty dummy entry */ > + .physmem.cnt = 0, /* empty dummy entry */ > .physmem.max = INIT_PHYSMEM_REGIONS, > #endif > > -- > 1.9.1 -- 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