From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 867CDC433E5 for ; Thu, 23 Jul 2020 11:31:03 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 5462E20709 for ; Thu, 23 Jul 2020 11:31:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="a67ZxAgM" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5462E20709 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=2d33yO8fqwnGIMX+yOXEygEUHQuJJ8PpQC5N0VM7GZc=; b=a67ZxAgM2Kz5Dc2aiez+XCdD0 1+LY0Lr0NdtQst6zQs1PycvjNi4SjSfX9fXXiN8KNmyNh7a2zXasbpEMuCwtecNmMd6ztW4kc/24H 11VpyhFglT0f14RgVkk8JBAQI3zmLa7eg9Xhm65k0cxUmfPV3KfXDbz/fbj1SwYEuQemgCNNOOIwM OFCJQvrQ6sO0sdlq4p0Lg06sEvrHdNYgmpOpeoQ+jh586JF1eu5iHaOeXUgXyJD1sg4q1E1zH4A1o QyPiLLarGY3pn5D3Q4bGkvQ+hm8e52sPsH/ABqmn4eZrH17JpmMXL1SuKwL6UxAyvYVrtoLHJGm5+ jHO6xfeYg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jyZPs-00018b-Aa; Thu, 23 Jul 2020 11:29:36 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jyZPp-000180-24 for linux-arm-kernel@lists.infradead.org; Thu, 23 Jul 2020 11:29:34 +0000 Received: from gaia (unknown [95.146.230.158]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4A9D120709; Thu, 23 Jul 2020 11:29:29 +0000 (UTC) Date: Thu, 23 Jul 2020 12:29:26 +0100 From: Catalin Marinas To: "liwei (CM)" Subject: Re: =?utf-8?B?562U5aSNOiDnrZTlpI06IFtQQVRD?= =?utf-8?Q?H=5D_arm64=3A_mm=3A_fre?= =?utf-8?Q?e?= unused memmap for sparse memory model that define VMEMMAP Message-ID: <20200723112926.GB7315@gaia> References: <20200721073203.107862-1-liwei213@huawei.com> <20200722060705.GK802087@linux.ibm.com> <1699CE87DE933F49876AD744B5DC140F2312E948@dggemm526-mbx.china.huawei.com> <20200722124910.GE27540@gaia> <1699CE87DE933F49876AD744B5DC140F2312F0D6@dggemm526-mbx.china.huawei.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1699CE87DE933F49876AD744B5DC140F2312F0D6@dggemm526-mbx.china.huawei.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200723_072933_215298_D6D46287 X-CRM114-Status: GOOD ( 21.35 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Song Bao Hua \(Barry Song\)" , "linux-arm-kernel@lists.infradead.org" , "steve.capper@arm.com" , "Chenfeng \(puck\)" , sujunfei , "linux-kernel@vger.kernel.org" , fengbaopeng , zhaojiapeng , "Xiaqing \(A\)" , Mike Rapoport , "will@kernel.org" , "nsaenzjulienne@suse.de" , butao Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Jul 22, 2020 at 01:40:34PM +0000, liwei (CM) wrote: > Catalin Marinas wrote: > > On Wed, Jul 22, 2020 at 08:41:17AM +0000, liwei (CM) wrote: > > > Mike Rapoport wrote: > > > > On Tue, Jul 21, 2020 at 03:32:03PM +0800, Wei Li wrote: > > > > > For the memory hole, sparse memory model that define > > > > > SPARSEMEM_VMEMMAP do not free the reserved memory for the page > > > > > map, this patch do it. > > > > > > > > Are there numbers showing how much memory is actually freed? > > > > > > > > The freeing of empty memmap would become rather complex with these > > > > changes, do the memory savings justify it? > > > > > > In the sparse memory model, the size of a section is 1 GB > > > (SECTION_SIZE_BITS 30) by default. > > > > Can we reduce SECTION_SIZE_BITS instead? Say 26? > > Yes, you are right, reduce SECTION_SIZE_BITS to 26 can save almost the > same memory as the patch. > > 1) However, it is not clear whether changing the section size has any > other impact. Well, we should analyse this. > 2) Just like the flat memory model and the sparse memory model that > does not define VMEMMAP, both of them have their own ways to free > unused memmap. I think we've given a similar way for sparse memory > define VMEMMAP. I think we did it for flatmem initially (on arm32) and added support for sparsemem later on, so free_unused_memmap() had to cope with sparse sections. On arm64 we introduced vmemmap support and didn't bother with the freeing at all because of the added complexity of the vmemmap page tables. I wonder whether we should just disallow flatmem and non-vmemmap sparsemem on arm64. Is there any value in keeping them around? > 3) This explicit free unused memmap method does reduce unnecessary > memory waste for users who do not notice the section size > modification. But if we changed SECTION_SIZE_BITS in the mainline kernel, then we wouldn't need additional code to free the unused memmap. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel