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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9AB04C4332F for ; Mon, 13 Nov 2023 15:04:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc: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=3UEY9VDgyQh9bHrjvVxyIJyj7ip6rFYujXm+ueKgSNg=; b=DAA4BtWgkMEgw1 OU2s2TpMRsdHXwT4sg9e9PKGHo5vqE+KK2nElJbSK0h7e0IEUyvbbuYIsbg6a4/J1j7DaMaSRYcoW iE29sU+/H7+/N9HKuXzGJ++rZ+tsBfyPl2+78ERI8MJHC4SWYbx6MurelA1KyvxeKhpqWAh9Xa5+/ udtSJnw0hqIeigZLoaEwbfIgTq39LnQOX6iNrd63ope8VxOYVKRQV+ud2bxSI76gpDTXOhmIrB4bk ycvHpxeKxHwORXEotS/fe5VJKtU2MtxuQJboDEMigRhVus3iAuRs6nFZqk7s0tcCIaCMeiJZz7vOB +XtexOtLBtlFgt2N/hUQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1r2YTz-00ECXi-1M; Mon, 13 Nov 2023 15:04:11 +0000 Received: from casper.infradead.org ([2001:8b0:10b:1236::1]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1r2YTy-00ECXY-0g for linux-arm-kernel@bombadil.infradead.org; Mon, 13 Nov 2023 15:04:10 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=ZBQ5a0hJZ/GfX0iieQrBicPR1Pwnet9ZpiDu5Dc5S8o=; b=T4JygIqSJTI4zR7pgmmCZFqPiE Cuix9/8FMuTEaTJ2GiTMl9zVm70vXXkZ30telLR0jR+fttKqiv5V2IP2m0FzipRM96jnQKHlprEFp Y+h+Vm4ZC7GbL8wCbkUDU3KWWJDC6ZH0dEuD8xWwQP2Tuxvkte3ZMeOX656eFiCraCyqwyGMCcXqf EH02CShkSiYi4LeGns/w5lXlFX6sJ3xDuO11lHlpIFNdBNMcR3vs1Sv77gtYx707ggQFx0YNwHod0 KHMYYStbY//caLhJTuoCHEiDIF4aN4bzXJt+eFXej+JH266hPBrLtvilWpxrxkRyBk0zhfrj3yOzS bnH1rYaQ==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1r2YTu-00EsZO-5e; Mon, 13 Nov 2023 15:04:06 +0000 Date: Mon, 13 Nov 2023 15:04:06 +0000 From: Matthew Wilcox To: Ryan Roberts Cc: John Hubbard , Andrew Morton , Yin Fengwei , David Hildenbrand , Yu Zhao , Catalin Marinas , Anshuman Khandual , Yang Shi , "Huang, Ying" , Zi Yan , Luis Chamberlain , Itaru Kitayama , "Kirill A. Shutemov" , David Rientjes , Vlastimil Babka , Hugh Dickins , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v6 0/9] variable-order, large folios for anonymous memory Message-ID: References: <20230929114421.3761121-1-ryan.roberts@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 Mon, Nov 13, 2023 at 10:19:48AM +0000, Ryan Roberts wrote: > On 13/11/2023 05:18, Matthew Wilcox wrote: > > My hope is to abolish the 64kB page size configuration. ie instead of > > using the mixture of page sizes that you currently are -- 64k and > > 1M (right? Order-0, and order-4) > > Not quite; the contpte-size for a 64K page size is 2M/order-5. (and yes, it is > 64K/order-4 for a 4K page size, and 2M/order-7 for a 16K page size. I agree that > intuitively you would expect the order to remain constant, but it doesn't). > > The "recommend" setting above will actually enable order-3 as well even though > there is no HW benefit to this. So the full set of available memory sizes here is: > > 64K/order-0, 512K/order-3, 2M/order-5, 512M/order-13 > > > , that 4k, 64k and 2MB (order-0, > > order-4 and order-9) will provide better performance. > > > > Have you run any experiements with a 4kB page size? > > Agree that would be interesting with 64K small-sized THP enabled. And I'd love > to get to a world were we universally deal in variable sized chunks of memory, > aligned on 4K boundaries. > > In my experience though, there are still some performance benefits to 64K base > page vs 4K+contpte; the page tables are more cache efficient for the former case > - 64K of memory is described by 8 bytes in the former vs 8x16=128 bytes in the > latter. In practice the HW will still only read 8 bytes in the latter but that's > taking up a full cache line vs the former where a single cache line stores 8x > 64K entries. This is going to depend on your workload though -- if you're using more 2MB than 64kB, you get to elide a layer of page table with 4k base, rather than taking up 4 cache lines with a 64k base. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel