From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f72.google.com (mail-it0-f72.google.com [209.85.214.72]) by kanga.kvack.org (Postfix) with ESMTP id AFF616B0338 for ; Thu, 17 Nov 2016 13:01:48 -0500 (EST) Received: by mail-it0-f72.google.com with SMTP id w132so131941712ita.1 for ; Thu, 17 Nov 2016 10:01:48 -0800 (PST) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id 66si3136127iox.230.2016.11.17.10.01.42 for ; Thu, 17 Nov 2016 10:01:42 -0800 (PST) Message-ID: <582DF05A.9050601@arm.com> Date: Thu, 17 Nov 2016 18:00:58 +0000 From: James Morse MIME-Version: 1.0 Subject: Re: [PATCH v27 1/9] memblock: add memblock_cap_memory_range() 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> In-Reply-To: <20161117111917.GA22855@arm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Will Deacon , AKASHI Takahiro Cc: 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 Hi Will, Akashi, 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... Thanks, James > case, we'd end up accidentally removing the map regions here. > > The existing code: > >> - /* remove all the MAP regions above the limit */ >> - for (i = end_rgn - 1; i >= start_rgn; i--) { >> - if (!memblock_is_nomap(&type->regions[i])) >> - memblock_remove_region(type, i); >> - } > > seems to handle this. -- 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