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=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL 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 6E346C4332D for ; Wed, 17 Mar 2021 19:14:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 24B4064F2B for ; Wed, 17 Mar 2021 19:14:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233170AbhCQTOO (ORCPT ); Wed, 17 Mar 2021 15:14:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60256 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232963AbhCQTNj (ORCPT ); Wed, 17 Mar 2021 15:13:39 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BCBFFC06174A for ; Wed, 17 Mar 2021 12:13:38 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id j19so39530ybg.5 for ; Wed, 17 Mar 2021 12:13:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=PMNTWEhfV6poxu3dvNBZ0UMNzT+uf6rEFOoHyvBSs4w=; b=NBYx9GkOp4RmsEoqQW1OUbK6Af2HZ+LSsowzg92soxTJILyt1ru0deBVCL4L1rv72R wNa5pP6KVc+qd2CwbKXOZPKQEI5zMGrWD+mA1YusfzJytS77RqUnsDx9WMaXglXnSDsx xcd2uhqLhA6g2U3Be8s572z9gjYEj4t6QyB64QOJBwwaAxcaOlwmWCgcmFXeyWI7RdPI Q+No5H0JfUdzubH73uOJNzHeifUE3NpHJ30yDQGj5uju9XNlysiYgOqPdje5/Cm3hLdd rEpgaya2cvWiZjPyi8MhqBCZ/UYMItUgSfbsDoIIhwe8WCOjDXAiGWa76x4x5bG8dZCo vLLQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=PMNTWEhfV6poxu3dvNBZ0UMNzT+uf6rEFOoHyvBSs4w=; b=k3qca8Hw9+YCDB3It7I7XGPU2WJW/6cDRgtDYRmTHuWzlIcSyN9X2pYxcWbb3yQE9y Av5jcuxGGCEZPSgRqUR7gRvbd+nffz/rjII4x8RXM1xAuS0Az0VcB1Q/QzRarfq8MF7M vtpgCoEFQsmQ6fvWoAFHwIOYjn9qLup2IEHZPRNDC9dPPgCbtwzqYD/tUetbwgX4Wy1q rtfEykBUIL6APdEeWtGr7/ZUGGCdyeKfNzp9QL1bVmpHRbqkjvUdoOuv7H18tL5nyioa Ofs0CsZ1f8bq/T6FXXy9H/LvooTalm8rsOBwJF9afjUyHGHQs+a0Sj1E3ymK2rJl7jON 2Wiw== X-Gm-Message-State: AOAM532zJE5Dd6pXkqBW+xqEPl6gsYiHCA79dgJyoi5zcyZUyY4AfcUJ c3HQk1iAhMOM4XbX2zDZkzn8w+yBFadR X-Google-Smtp-Source: ABdhPJxEU/NDufnze3h7G0LVZg2aYOx4qJg+j9BSn1s+iC2EzMHJDDyEnwUZx76eo1cN/PimKfC47lJ2IHEe X-Received: from bg.sfo.corp.google.com ([2620:15c:8:10:8c6a:2e6f:ed81:d930]) (user=bgeffon job=sendgmr) by 2002:a25:d155:: with SMTP id i82mr6299882ybg.404.1616008417952; Wed, 17 Mar 2021 12:13:37 -0700 (PDT) Date: Wed, 17 Mar 2021 12:13:33 -0700 In-Reply-To: <20210303175235.3308220-1-bgeffon@google.com> Message-Id: <20210317191334.564944-1-bgeffon@google.com> Mime-Version: 1.0 References: <20210303175235.3308220-1-bgeffon@google.com> X-Mailer: git-send-email 2.31.0.rc2.261.g7f71774620-goog Subject: [PATCH v2 1/2] mm: Allow non-VM_DONTEXPAND and VM_PFNMAP mappings with MREMAP_DONTUNMAP From: Brian Geffon To: Andrew Morton Cc: Axel Rasmussen , Lokesh Gidra , Mike Rapoport , Peter Xu , Hugh Dickins , "Michael S . Tsirkin" , Brian Geffon , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andy Lutomirski , Vlastimil Babka , Andrea Arcangeli , Sonny Rao , Minchan Kim , "Kirill A . Shutemov" , Dmitry Safonov Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently MREMAP_DONTUNMAP only accepts private anonymous mappings. This change will widen the support to include any mappings which are not VM_DONTEXPAND or VM_PFNMAP. The primary use case is to support MREMAP_DONTUNMAP on mappings which may have been created from a memfd. This change which takes advantage of the existing check in vma_to_resize for non-VM_DONTEXPAND and non-VM_PFNMAP mappings will cause MREMAP_DONTUNMAP to return -EFAULT if such mappings are remapped. This behavior is consistent with existing behavior when using mremap with such mappings. Lokesh Gidra who works on the Android JVM, provided an explanation of how such a feature will improve Android JVM garbage collection: "Android is developing a new garbage collector (GC), based on userfaultfd. The garbage collector will use userfaultfd (uffd) on the java heap during compaction. On accessing any uncompacted page, the application threads will find it missing, at which point the thread will create the compacted page and then use UFFDIO_COPY ioctl to get it mapped and then resume execution. Before starting this compaction, in a stop-the-world pause the heap will be mremap(MREMAP_DONTUNMAP) so that the java heap is ready to receive UFFD_EVENT_PAGEFAULT events after resuming execution. To speedup mremap operations, pagetable movement was optimized by moving PUD entries instead of PTE entries [1]. It was necessary as mremap of even modest sized memory ranges also took several milliseconds, and stopping the application for that long isn't acceptable in response-time sensitive cases. With UFFDIO_CONTINUE feature [2], it will be even more efficient to implement this GC, particularly the 'non-moveable' portions of the heap. It will also help in reducing the need to copy (UFFDIO_COPY) the pages. However, for this to work, the java heap has to be on a 'shared' vma. Currently MREMAP_DONTUNMAP only supports private anonymous mappings, this patch will enable using UFFDIO_CONTINUE for the new userfaultfd-based heap compaction." [1] https://lore.kernel.org/linux-mm/20201215030730.NC3CU98e4%25akpm@linux-foundation.org/ [2] https://lore.kernel.org/linux-mm/20210302000133.272579-1-axelrasmussen@google.com/ Signed-off-by: Brian Geffon --- mm/mremap.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/mm/mremap.c b/mm/mremap.c index ec8f840399ed..2c57dc4bc8b6 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -653,10 +653,6 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr, return ERR_PTR(-EINVAL); } - if (flags & MREMAP_DONTUNMAP && (!vma_is_anonymous(vma) || - vma->vm_flags & VM_SHARED)) - return ERR_PTR(-EINVAL); - if (is_vm_hugetlb_page(vma)) return ERR_PTR(-EINVAL); -- 2.31.0.rc2.261.g7f71774620-goog