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[23.128.96.18]) by mx.google.com with ESMTP id f25si1369093ejb.519.2020.09.30.08.26.40; Wed, 30 Sep 2020 08:27:03 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=Ouhunx+Q; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728496AbgI3PZh (ORCPT + 99 others); Wed, 30 Sep 2020 11:25:37 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:31767 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725799AbgI3PZg (ORCPT ); Wed, 30 Sep 2020 11:25:36 -0400 Dkim-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1601479534; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=ULbhIL/q0cLG65xaFbVUTBshEy8FHXvXhINnXmLRfqc=; b=Ouhunx+QRlBcjBgumsVA/QY0EUUh1yT5x9L83/gUaHJTEo1XtYRl6y9sGy2Pnnk+osseLy RD6GfSazISYNq/5jsJBzqjaVYPo41BbK5fR89TFNOaMfwyer4JyP04LAiWvMHlCS6TAueY jo+kpteZnaNjVawWvYYjqhezJm/eInc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-167-vtD09YPQPl2abOAtTVC-OA-1; Wed, 30 Sep 2020 11:25:29 -0400 X-MC-Unique: vtD09YPQPl2abOAtTVC-OA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EE1CD81CB07; Wed, 30 Sep 2020 15:25:24 +0000 (UTC) Received: from [10.36.113.220] (ovpn-113-220.ams2.redhat.com [10.36.113.220]) by smtp.corp.redhat.com (Postfix) with ESMTP id 859A11001901; Wed, 30 Sep 2020 15:25:16 +0000 (UTC) Subject: Re: [PATCH v6 5/6] mm: secretmem: use PMD-size pages to amortize direct map fragmentation To: jejb@linux.ibm.com, Mike Rapoport , Peter Zijlstra Cc: Mike Rapoport , Andrew Morton , Alexander Viro , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christopher Lameter , Dan Williams , Dave Hansen , Elena Reshetova , "H. Peter Anvin" , Idan Yaniv , Ingo Molnar , "Kirill A. Shutemov" , Matthew Wilcox , Mark Rutland , Michael Kerrisk , Palmer Dabbelt , Paul Walmsley , Thomas Gleixner , Shuah Khan , Tycho Andersen , Will Deacon , linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org, x86@kernel.org References: <20200924132904.1391-1-rppt@kernel.org> <20200924132904.1391-6-rppt@kernel.org> <20200925074125.GQ2628@hirez.programming.kicks-ass.net> <20200929130529.GE2142832@kernel.org> <20200929141216.GO2628@hirez.programming.kicks-ass.net> <20200929145813.GA3226834@linux.ibm.com> <20200929151552.GS2628@hirez.programming.kicks-ass.net> <20200930102745.GC3226834@linux.ibm.com> <371c27d97067654171e5c1019340b56cffadae7a.camel@linux.ibm.com> <6568383f-4e43-2fe4-ecf1-8a55e306440b@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30.09.20 17:17, James Bottomley wrote: > On Wed, 2020-09-30 at 16:45 +0200, David Hildenbrand wrote: >> On 30.09.20 16:39, James Bottomley wrote: >>> On Wed, 2020-09-30 at 13:27 +0300, Mike Rapoport wrote: >>>> On Tue, Sep 29, 2020 at 05:15:52PM +0200, Peter Zijlstra wrote: >>>>> On Tue, Sep 29, 2020 at 05:58:13PM +0300, Mike Rapoport wrote: >>>>>> On Tue, Sep 29, 2020 at 04:12:16PM +0200, Peter Zijlstra >>>>>> wrote: >>>>>>> It will drop them down to 4k pages. Given enough inodes, >>>>>>> and allocating only a single sekrit page per pmd, we'll >>>>>>> shatter the directmap into 4k. >>>>>> >>>>>> Why? Secretmem allocates PMD-size page per inode and uses it >>>>>> as a pool of 4K pages for that inode. This way it ensures >>>>>> that __kernel_map_pages() is always called on PMD boundaries. >>>>> >>>>> Oh, you unmap the 2m page upfront? I read it like you did the >>>>> unmap at the sekrit page alloc, not the pool alloc side of >>>>> things. >>>>> >>>>> Then yes, but then you're wasting gobs of memory. Basically you >>>>> can pin 2M per inode while only accounting a single page. >>>> >>>> Right, quite like THP :) >>>> >>>> I considered using a global pool of 2M pages for secretmem and >>>> handing 4K pages to each inode from that global pool. But I've >>>> decided to waste memory in favor of simplicity. >>> >>> I can also add that the user space consumer of this we wrote does >>> its user pool allocation at a 2M granularity, so nothing is >>> actually wasted. >> >> ... for that specific user space consumer. (or am I missing >> something?) > > I'm not sure I understand what you mean? It's designed to be either > the standard wrapper or an example of how to do the standard wrapper > for the syscall. It uses the same allocator system glibc uses for > malloc/free ... which pretty much everyone uses instead of calling > sys_brk directly. If you look at the granularity glibc uses for > sys_brk, it's not 4k either. Okay thanks, "the user space consumer of this we wrote" didn't sound as generic to me as "the standard wrapper". -- Thanks, David / dhildenb