Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754050AbdCBGO4 (ORCPT ); Thu, 2 Mar 2017 01:14:56 -0500 Received: from szxga01-in.huawei.com ([45.249.212.187]:3344 "EHLO dggrg01-dlp.huawei.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1750771AbdCBGOy (ORCPT ); Thu, 2 Mar 2017 01:14:54 -0500 Subject: Re: [PATCH] mm: free reserved area's memmap if possiable To: Jisheng Zhang , Chen Feng , Catalin Marinas References: <1486987349-58711-1-git-send-email-zhouxianrong@huawei.com> <1487055180-128750-1-git-send-email-zhouxianrong@huawei.com> <04630153-bc82-ac1f-2f80-344c90200732@huawei.com> <20170301184140.7ac9de0a@xhacker> CC: Ard Biesheuvel , "linux-mm@kvack.org" , Mark Rutland , Kefeng Wang , , , Will Deacon , , , , Alexander Kuleshov , , , , , "linux-arm-kernel@lists.infradead.org" , Steve Capper , "linux-kernel@vger.kernel.org" , Joe Perches , Dennis Chen , Andrew Morton , Ganapatrao Kulkarni From: zhouxianrong Message-ID: Date: Thu, 2 Mar 2017 14:00:27 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:45.0) Gecko/20100101 Thunderbird/45.0 MIME-Version: 1.0 In-Reply-To: <20170301184140.7ac9de0a@xhacker> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.142.145.228] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A020204.58B7B50E.030F,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2014-11-16 11:51:01, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: afe148ac174f387a48f00c54456fe87b Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4125 Lines: 110 On 2017/3/1 18:41, Jisheng Zhang wrote: > Add Chen, Catalin > > On Thu, 16 Feb 2017 09:11:29 +0800 zhouxianrong wrote: >> >> >> On 2017/2/15 15:10, Ard Biesheuvel wrote: >>> On 15 February 2017 at 01:44, zhouxianrong wrote: >>>> >>>> >>>> On 2017/2/14 17:03, Ard Biesheuvel wrote: >>>>> >>>>> On 14 February 2017 at 06:53, wrote: >>>>>> >>>>>> From: zhouxianrong >>>>>> >>>>>> just like freeing no-map area's memmap (gaps of memblock.memory) >>>>>> we could free reserved area's memmap (areas of memblock.reserved) >>>>>> as well only when user of reserved area indicate that we can do >>>>>> this in drivers. that is, user of reserved area know how to >>>>>> use the reserved area who could not memblock_free or free_reserved_xxx >>>>>> the reserved area and regard the area as raw pfn usage by kernel. >>>>>> the patch supply a way to users who want to utilize the memmap >>>>>> memory corresponding to raw pfn reserved areas as many as possible. >>>>>> users can do this by memblock_mark_raw_pfn interface which mark the >>>>>> reserved area as raw pfn and tell free_unused_memmap that this area's >>>>>> memmap could be freeed. >>>>>> >>>>> >>>>> Could you give an example how much memory we actually recover by doing >>>>> this? I understand it depends on the size of the reserved regions, but >>>>> I'm sure you have an actual example that inspired you to write this >>>>> patch. >>>> >>>> >>>> i did statistics in our platform, the memmap of reserved region that can be >>>> freed >>>> is about 6MB. it's fewer. > > <...> > >>>>> In any case, it is good to emphasize that on 4 KB pagesize kernels, we >>>>> will only free multiples of 8 MB that are 8 MB aligned, resulting in >>>>> 128 KB of memmap backing to be released. >>>> >>>> >>>> >>>>> >>>>> >>>>>> + if (start < end) >>>>>> + free_memmap(start, end); >>>>>> + } >>>>>> } >>>>>> #endif /* !CONFIG_SPARSEMEM_VMEMMAP */ >>>>>> >>>>>> diff --git a/include/linux/memblock.h b/include/linux/memblock.h >>>>>> index 5b759c9..9f8d277 100644 >>>>>> --- a/include/linux/memblock.h >>>>>> +++ b/include/linux/memblock.h >>>>>> @@ -26,6 +26,7 @@ enum { >>>>>> MEMBLOCK_HOTPLUG = 0x1, /* hotpluggable region */ >>>>>> MEMBLOCK_MIRROR = 0x2, /* mirrored region */ >>>>>> MEMBLOCK_NOMAP = 0x4, /* don't add to kernel direct >>>>>> mapping */ >>>>>> + MEMBLOCK_RAW_PFN = 0x8, /* region whose memmap never be >>>>>> used */ >>>>> >>>>> >>>>> I think we should be *very* careful about the combinatorial explosion >>>>> that results when combining all these flags, given that this is not a >>>>> proper enum but a bit field. >>>>> >>>>> In any case, the generic memblock change should be in a separate patch >>>>> from the arm64 change. >>>> >>>> >>>> MEMBLOCK_RAW_PFN and MEMBLOCK_NOMAP can not be set at the same time >>>> >>> >>> They should not. But if I call memblock_mark_raw_pfn() on a >>> MEMBLOCK_NOMAP region, it will have both flags set. >>> >>> In summary, I don't think we need this patch. And if you can convince >>> us otherwise, you should really be more methodical and explicit in >>> implementing this RAW_PFN flag, not add it as a byproduct of the arch >>> code that uses it. Also, you should explain how RAW_PFN relates to >>> NOMAP, and ensure that RAW_PFN and NOMAP regions don't intersect if >>> that is an unsupported combination. >> >> yes, setting both MEMBLOCK_RAW_PFN and MEMBLOCK_NOMAP could meet some problems >> when gaps of memblock.memory intersect memblock.reserved. if they do not intersect, >> that's ok. so as you said this should be carefully considered. >> >> as you think this patch is not needed because, i have showed my idea, it's enough, thanks! > > we are also interested in this area. > > Just curious, is this patch to "free the vmemmap holes" mentioned by > by Catalin in [1]? free the vmemmap of reserved memblock (other than no-map regions) whose driver owner know it is never be used. > > [1]http://lkml.iu.edu/hypermail/linux/kernel/1604.1/03036.html > > . >