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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 1D808C2BA19 for ; Tue, 14 Apr 2020 07:23:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DD88C20767 for ; Tue, 14 Apr 2020 07:23:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="qLkt2QBy" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2406561AbgDNHX0 (ORCPT ); Tue, 14 Apr 2020 03:23:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57000 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2406537AbgDNHXW (ORCPT ); Tue, 14 Apr 2020 03:23:22 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D362FC0A3BDC for ; Tue, 14 Apr 2020 00:23:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=mdGWbEV2x2kdC5wG9BfGG6AGALuiWCVT7ddOuw0GXRY=; b=qLkt2QBytR7Fe51p8cO9Vf1/b+ xVWJ54SX12vGaW73vd8QVrGX2oOs6tuvshDuNsiOG092Sk/g+URdUovwJaGYErHwBF5T8E6Lp2fHN /WmGdzZtBqaHcPvJJ3Nw6nEmmi7aFjVVA4oUO/cNoZpTLFvrmZI5F8EIVK8CLRuESs4y3wtOIzyZK ziMikLkYeLjZRLKMAEpxQUXD4SGIuTB75jdLgURHQtMtOZ1LZvIcplWcWz42HO/zoPsVHPFbsHoX6 yK2I/42COQYUkVKZqfG3oNqU3bkmZABO/wik26fvtLOpzEv4j87Fc3ohFq5uw9DHocMoxwNPcQZVy bemhMBGA==; Received: from hch by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jOFue-0002Dm-Hj; Tue, 14 Apr 2020 07:23:16 +0000 Date: Tue, 14 Apr 2020 00:23:16 -0700 From: Christoph Hellwig To: Nicholas Piggin Cc: linux-mm@kvack.org, linux-arch@vger.kernel.org, Catalin Marinas , x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Thomas Gleixner , Will Deacon , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 4/4] mm/vmalloc: Hugepage vmalloc mappings Message-ID: <20200414072316.GA5503@infradead.org> References: <20200413125303.423864-1-npiggin@gmail.com> <20200413125303.423864-5-npiggin@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200413125303.423864-5-npiggin@gmail.com> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 13, 2020 at 10:53:03PM +1000, Nicholas Piggin wrote: > For platforms that define HAVE_ARCH_HUGE_VMAP and support PMD vmap mappings, > have vmalloc attempt to allocate PMD-sized pages first, before falling back > to small pages. Allocations which use something other than PAGE_KERNEL > protections are not permitted to use huge pages yet, not all callers expect > this (e.g., module allocations vs strict module rwx). > > This gives a 6x reduction in dTLB misses for a `git diff` (of linux), from > 45600 to 6500 and a 2.2% reduction in cycles on a 2-node POWER9. > > This can result in more internal fragmentation and memory overhead for a > given allocation. It can also cause greater NUMA unbalance on hashdist > allocations. > > There may be other callers that expect small pages under vmalloc but use > PAGE_KERNEL, I'm not sure if it's feasible to catch them all. An > alternative would be a new function or flag which enables large mappings, > and use that in callers. Why do we even use vmalloc in this case rather than just doing a huge page allocation? What callers are you intersted in?