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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 AB340C64EB0 for ; Tue, 9 Oct 2018 21:39:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6372E214DC for ; Tue, 9 Oct 2018 21:39:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6372E214DC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727591AbeJJE55 (ORCPT ); Wed, 10 Oct 2018 00:57:57 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:50330 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725837AbeJJE55 (ORCPT ); Wed, 10 Oct 2018 00:57:57 -0400 Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 602068E2; Tue, 9 Oct 2018 21:39:00 +0000 (UTC) Date: Tue, 9 Oct 2018 14:38:59 -0700 From: Andrew Morton To: "Joel Fernandes (Google)" Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@android.com, minchan@google.com, hughd@google.com, lokeshgidra@google.com, Greg Kroah-Hartman , Kate Stewart , Philippe Ombredanne , Thomas Gleixner Subject: Re: [PATCH] mm: Speed up mremap on large regions Message-Id: <20181009143859.8b9a700b1caf4e8d1e33a723@linux-foundation.org> In-Reply-To: <20181009201400.168705-1-joel@joelfernandes.org> References: <20181009201400.168705-1-joel@joelfernandes.org> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 9 Oct 2018 13:14:00 -0700 "Joel Fernandes (Google)" wrote: > Android needs to mremap large regions of memory during memory management > related operations. The mremap system call can be really slow if THP is > not enabled. The bottleneck is move_page_tables, which is copying each > pte at a time, and can be really slow across a large map. Turning on THP > may not be a viable option, and is not for us. This patch speeds up the > performance for non-THP system by copying at the PMD level when possible. > > The speed up is three orders of magnitude. On a 1GB mremap, the mremap > completion times drops from 160-250 millesconds to 380-400 microseconds. > > Before: > Total mremap time for 1GB data: 242321014 nanoseconds. > Total mremap time for 1GB data: 196842467 nanoseconds. > Total mremap time for 1GB data: 167051162 nanoseconds. > > After: > Total mremap time for 1GB data: 385781 nanoseconds. > Total mremap time for 1GB data: 388959 nanoseconds. > Total mremap time for 1GB data: 402813 nanoseconds. > > Incase THP is enabled, the optimization is skipped. I also flush the > tlb every time we do this optimization since I couldn't find a way to > determine if the low-level PTEs are dirty. It is seen that the cost of > doing so is not much compared the improvement, on both x86-64 and arm64. Looks tasty. > --- a/mm/mremap.c > +++ b/mm/mremap.c > @@ -191,6 +191,54 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, > drop_rmap_locks(vma); > } > > +bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr, I'll park this for now, shall plan to add a `static' in there then merge it up after 4.20-rc1.