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Wed, 30 Sep 2020 10:45:30 -0400 X-MC-Unique: e6gCzBMwNE6TrMjfCM972g-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 95B9B1018F65; Wed, 30 Sep 2020 14:45:25 +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 A62D95579B; Wed, 30 Sep 2020 14:45:12 +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 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> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <371c27d97067654171e5c1019340b56cffadae7a.camel@linux.ibm.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200930_104535_261520_545B1ECA X-CRM114-Status: GOOD ( 21.26 ) 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: Mark Rutland , Catalin Marinas , Dave Hansen , linux-mm@kvack.org, Will Deacon , linux-kselftest@vger.kernel.org, "H. Peter Anvin" , Christopher Lameter , Shuah Khan , Dan Williams , Elena Reshetova , linux-arch@vger.kernel.org, Tycho Andersen , linux-nvdimm@lists.01.org, Idan Yaniv , x86@kernel.org, Matthew Wilcox , Ingo Molnar , Michael Kerrisk , Arnd Bergmann , Borislav Petkov , Alexander Viro , Andy Lutomirski , Paul Walmsley , "Kirill A. Shutemov" , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Palmer Dabbelt , linux-fsdevel@vger.kernel.org, Andrew Morton , Mike Rapoport 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 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?) -- Thanks, David / dhildenb _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel