From: Paolo Bonzini Subject: Re: fstrim has no effect on a just-mounted filesystem Date: Wed, 12 Mar 2014 19:10:42 +0100 Message-ID: <5320A322.7020009@redhat.com> References: <20140311213932.GA19176@redhat.com> <531F8456.2020404@redhat.com> <20140311220013.GV1346@redhat.com> <531F8953.1030702@redhat.com> <20140311225932.GW1346@redhat.com> <20140311230715.GA19648@redhat.com> <531F97A8.2020905@redhat.com> <20140311233047.GX1346@redhat.com> <20140312100507.GA19635@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-ext4@vger.kernel.org To: "Richard W.M. Jones" , Eric Sandeen Return-path: Received: from mx1.redhat.com ([209.132.183.28]:52956 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755808AbaCLSKu (ORCPT ); Wed, 12 Mar 2014 14:10:50 -0400 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id s2CIAjPt030160 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Wed, 12 Mar 2014 14:10:46 -0400 In-Reply-To: <20140312100507.GA19635@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: Il 12/03/2014 11:17, Richard W.M. Jones ha scritto: > Somewhere, the discard requests are disappearing in the stack (or more > likely, being delayed). blktrace/trace-cmd somehow forces them out. > But fsync/sync/umount/sleep does not. They might be stuck in qemu too ... No, this I can be quite sure about. QEMU sends them as soon as they are received in the SCSI layer. If they were ill-formed, QEMU would fail them. If they got stuck, sooner or later you'd not be able to do I/O anymore (there is a queue depth limit) and the guest would start getting timeouts. Also, certainly blktrace would have no effect on QEMU. Paolo