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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 2CF71C433E0 for ; Fri, 15 May 2020 18:38:26 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E00272070A for ; Fri, 15 May 2020 18:38:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="HG4DgOUI" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E00272070A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:35072 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jZfE1-00030U-2t for qemu-devel@archiver.kernel.org; Fri, 15 May 2020 14:38:25 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:52632) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jZfCn-0002Bc-9M for qemu-devel@nongnu.org; Fri, 15 May 2020 14:37:09 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:20871 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jZfCl-0002v0-SR for qemu-devel@nongnu.org; Fri, 15 May 2020 14:37:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1589567826; 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=iS2BZEZhYnHE5mi0Tf0cUE2Vbxbk8ajM07NE1jWnMoA=; b=HG4DgOUIcBLWUcwjmssNuVyPsSwcepB0oWK4PhVdXwZyMbrSSKtpzCSiA4EFK5+ALHrZI9 zQQ9kY6p+UlHaLjRo72vi/3HJWWvkDp8leJqL4LioG6yi9G5qIl1Eks3LUdS+cRckv663a vgc4H9vPChxswmC8Tlu667GqHf7PuFs= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-466-Zy5vaWusMkeTl9eED5XF2g-1; Fri, 15 May 2020 14:37:04 -0400 X-MC-Unique: Zy5vaWusMkeTl9eED5XF2g-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9B7B480B73A; Fri, 15 May 2020 18:37:03 +0000 (UTC) Received: from work-vm (ovpn-114-149.ams2.redhat.com [10.36.114.149]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0F3725C3E7; Fri, 15 May 2020 18:36:54 +0000 (UTC) Date: Fri, 15 May 2020 19:36:52 +0100 From: "Dr. David Alan Gilbert" To: David Hildenbrand Subject: Re: [PATCH v1 07/17] migration/rdma: Use ram_block_discard_set_broken() Message-ID: <20200515183652.GM2954@work-vm> References: <20200506094948.76388-1-david@redhat.com> <20200506094948.76388-8-david@redhat.com> <20200515124501.GE2954@work-vm> <96a58e88-2629-f2ee-5884-38d11e571548@redhat.com> <20200515175105.GL2954@work-vm> <1cac6cb0-7804-bab2-4ecf-044c369c1135@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1cac6cb0-7804-bab2-4ecf-044c369c1135@redhat.com> User-Agent: Mutt/1.13.4 (2020-02-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Received-SPF: pass client-ip=205.139.110.120; envelope-from=dgilbert@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/14 23:27:07 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_PASS=-0.001, T_HK_NAME_DR=0.01 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Eduardo Habkost , kvm@vger.kernel.org, "Michael S . Tsirkin" , Juan Quintela , qemu-devel@nongnu.org, qemu-s390x@nongnu.org, Paolo Bonzini , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * David Hildenbrand (david@redhat.com) wrote: > On 15.05.20 19:51, Dr. David Alan Gilbert wrote: > > * David Hildenbrand (david@redhat.com) wrote: > >> On 15.05.20 14:45, Dr. David Alan Gilbert wrote: > >>> * David Hildenbrand (david@redhat.com) wrote: > >>>> RDMA will pin all guest memory (as documented in docs/rdma.txt). We want > >>>> to mark RAM block discards to be broken - however, to keep it simple > >>>> use ram_block_discard_is_required() instead of inhibiting. > >>> > >>> Should this be dependent on whether rdma->pin_all is set? > >>> Even with !pin_all some will be pinned at any given time > >>> (when it's registered with the rdma stack). > >> > >> Do you know how much memory this is? Is such memory only temporarily pinned? > > > > With pin_all not set, only a subset of memory, I think multiple 1MB > > chunks, are pinned at any one time. > > > >> At least with special-cases of vfio, it's acceptable if some memory is > >> temporarily pinned - we assume it's only the working set of the driver, > >> which guests will not inflate as long as they don't want to shoot > >> themselves in the foot. > >> > >> This here sounds like the guest does not know the pinned memory is > >> special, right? > > > > Right - for RDMA it's all of memory that's being transferred, and the > > guest doesn't see when each part is transferred. > > > Okay, so all memory will eventually be pinned, just not at the same > time, correct? > > I think this implies that any memory that was previously discarded will > be backed my new pages, meaning we will consume more memory than intended. > > If so, always disabling discarding of RAM seems to be the right thing to do. Yeh that's probably true, although there's a check for 'buffer_is_zero' in the !rdma->pin_all case, if the entire area is zero (or probably if unmapped) then it sends a notification rather than registering; see qemu_rdma_write_one and search for 'This chunk has not yet been registered, so first check to see' Dave > > -- > Thanks, > > David / dhildenb -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK