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=-16.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 1E61FC433E0 for ; Wed, 17 Mar 2021 20:41:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CF50E64E74 for ; Wed, 17 Mar 2021 20:41:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233449AbhCQUku (ORCPT ); Wed, 17 Mar 2021 16:40:50 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:43122 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231920AbhCQUkY (ORCPT ); Wed, 17 Mar 2021 16:40:24 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1616013623; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Y409+hbMmdUUFTiOqanFc/IWp7lWurY/OstZudlxMGI=; b=WDQC3d6NqBDluSuMQBJdQiDqieir/Gb4KnF05fyop1gp46dYnThHmGYko5efYRj0TWOq/6 SnuURKjL/+/2WfJgLWlfNWmJxNt+ppxuqBK3pCbTdbbSEdQ4yWXorVZ+A11ZMxRLQ1SO7g 62/RTFSY9q0bITQhATOUQ+9m5Zid/CA= Received: from mail-qk1-f197.google.com (mail-qk1-f197.google.com [209.85.222.197]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-601-priFkR8cNKOKWybEoEZzbg-1; Wed, 17 Mar 2021 16:40:20 -0400 X-MC-Unique: priFkR8cNKOKWybEoEZzbg-1 Received: by mail-qk1-f197.google.com with SMTP id b78so30197211qkg.13 for ; Wed, 17 Mar 2021 13:40:20 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=Y409+hbMmdUUFTiOqanFc/IWp7lWurY/OstZudlxMGI=; b=gF7a+g9+Ckn30dRnXTGgjft9SKK47ANxPBK1j9z57XolCboYdCHg9JSoXaH0UJKmNI UEGX96kKK9xrVnhqC28Vmg+61Cc5+G195Vf8If38YgAymIKyA1kcpnrt8j2hKfj8a5vF 6yb+Ve8ntEyo1hrrwDOPDZE0XwlxIVcLp+L5iOjT0l5jV8pQ5Wd4gHm7qd/KMKi+MW9W 1jPhak91b4UiyIovioh2dBtWqn+92n/6+F9Ol4HZvF4vFm7u3O6z4YvgYOHNhA9jd/DB lM/f06YHx2P8aSx6OT+wt+KAdQ1AELIoUBTpaywPLymPK86KKdrRlVN7zCVe7BDiTnux bw/w== X-Gm-Message-State: AOAM533dNRWeJulYOPzrjCc2oo/Fr7ggbkaDc14yDZYfxF9q6hgmjkBW 2THYEtk62DzrDJy6EPqJ6z28/qcAQiOjUwrnEYC130U+rTe47d74rzD82RY9gl+h3F9xTEzodmw ZekQ9XpT6DxyEZHzEM/vmZpwR X-Received: by 2002:a37:7006:: with SMTP id l6mr1112499qkc.137.1616013619518; Wed, 17 Mar 2021 13:40:19 -0700 (PDT) X-Google-Smtp-Source: ABdhPJzAO2RnKvysnz5AJ2MhEmACHRCP/slH3sKue7aceM79G8SFp4fSuy7PZcfMdyA5pFmgw02GQQ== X-Received: by 2002:a37:7006:: with SMTP id l6mr1112476qkc.137.1616013619214; Wed, 17 Mar 2021 13:40:19 -0700 (PDT) Received: from xz-x1 ([142.126.89.138]) by smtp.gmail.com with ESMTPSA id j6sm14931770qtx.14.2021.03.17.13.40.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Mar 2021 13:40:18 -0700 (PDT) Date: Wed, 17 Mar 2021 16:40:15 -0400 From: Peter Xu To: Brian Geffon Cc: Andrew Morton , Axel Rasmussen , Lokesh Gidra , Mike Rapoport , Hugh Dickins , "Michael S . Tsirkin" , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andy Lutomirski , Vlastimil Babka , Andrea Arcangeli , Sonny Rao , Minchan Kim , "Kirill A . Shutemov" , Dmitry Safonov Subject: Re: [PATCH v2 1/2] mm: Allow non-VM_DONTEXPAND and VM_PFNMAP mappings with MREMAP_DONTUNMAP Message-ID: <20210317204015.GM395976@xz-x1> References: <20210303175235.3308220-1-bgeffon@google.com> <20210317191334.564944-1-bgeffon@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210317191334.564944-1-bgeffon@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Brian, On Wed, Mar 17, 2021 at 12:13:33PM -0700, Brian Geffon wrote: > 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); The code change seems to be not aligned with what the commit message said. Did you perhaps forget to add the checks against VM_DONTEXPAND | VM_PFNMAP? I'm guessing that (instead of commit message to be touched up) because you still attached the revert patch, then that check seems to be needed. Thanks, -- Peter Xu