From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 55B106B040D for ; Fri, 18 Nov 2016 07:10:38 -0500 (EST) Received: by mail-pf0-f200.google.com with SMTP id 83so140804359pfx.1 for ; Fri, 18 Nov 2016 04:10:38 -0800 (PST) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id a3si7996936pgc.167.2016.11.18.04.10.37 for ; Fri, 18 Nov 2016 04:10:37 -0800 (PST) Date: Fri, 18 Nov 2016 12:10:36 +0000 From: Will Deacon Subject: Re: [PATCH v27 1/9] memblock: add memblock_cap_memory_range() Message-ID: <20161118121036.GK13470@arm.com> References: <20161102044959.11954-1-takahiro.akashi@linaro.org> <20161102045153.12008-1-takahiro.akashi@linaro.org> <20161110172720.GB17134@arm.com> <20161111025049.GG381@linaro.org> <20161111031903.GB15997@arm.com> <20161114055515.GH381@linaro.org> <20161116163015.GM7928@arm.com> <20161117022023.GA5704@linaro.org> <20161117111917.GA22855@arm.com> <582DF05A.9050601@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <582DF05A.9050601@arm.com> Sender: owner-linux-mm@kvack.org List-ID: To: James Morse Cc: AKASHI Takahiro , Dennis Chen , catalin.marinas@arm.com, akpm@linux-foundation.org, geoff@infradead.org, bauerman@linux.vnet.ibm.com, dyoung@redhat.com, mark.rutland@arm.com, kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.orgnd@arm.com On Thu, Nov 17, 2016 at 06:00:58PM +0000, James Morse wrote: > On 17/11/16 11:19, Will Deacon wrote: > > It looks much better, thanks! Just one question below. > > > > > On Thu, Nov 17, 2016 at 02:34:24PM +0900, AKASHI Takahiro wrote: > >> diff --git a/mm/memblock.c b/mm/memblock.c > >> index 7608bc3..fea1688 100644 > >> --- a/mm/memblock.c > >> +++ b/mm/memblock.c > >> @@ -1514,11 +1514,37 @@ void __init memblock_enforce_memory_limit(phys_addr_t limit) > >> (phys_addr_t)ULLONG_MAX); > >> } > >> > >> +void __init memblock_cap_memory_range(phys_addr_t base, phys_addr_t size) > >> +{ > >> + int start_rgn, end_rgn; > >> + int i, ret; > >> + > >> + if (!size) > >> + return; > >> + > >> + ret = memblock_isolate_range(&memblock.memory, base, size, > >> + &start_rgn, &end_rgn); > >> + if (ret) > >> + return; > >> + > >> + /* remove all the MAP regions */ > >> + for (i = memblock.memory.cnt - 1; i >= end_rgn; i--) > >> + if (!memblock_is_nomap(&memblock.memory.regions[i])) > >> + memblock_remove_region(&memblock.memory, i); > > > > In the case that we have only one, giant memblock that covers base all > > of base + size, can't we end up with start_rgn = end_rgn = 0? In which > > Can this happen? If we only have one memblock that exactly spans > base:(base+size), memblock_isolate_range() will hit the '@rgn is fully > contained, record it' code and set start_rgn=0,end_rgn=1. (rbase==base, > rend==end). We only go round the loop once. > > If we only have one memblock that is bigger than base:(base+size) we end up with > three regions, start_rgn=1,end_rgn=2. The trickery here is the '@rgn intersects > from above' code decreases the loop counter so we process the same entry twice, > hitting '@rgn is fully contained, record it' the second time round... so we go > round the loop four times. > > I can't see how we hit the: > > if (rbase >= end) > > break; > > if (rend <= base) > > continue; > > code in either case... I consistently misread that as rend >= end and rbase <= base! In which case, I agree with your analysis: Reviewed-by: Will Deacon The patch could probably still use an ack from an mm person. Will -- 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