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=-17.9 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,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 B4761C433E0 for ; Fri, 12 Feb 2021 09:26:59 +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 0A89364DCE for ; Fri, 12 Feb 2021 09:26:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0A89364DCE 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]:52262 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lAUj4-00024p-12 for qemu-devel@archiver.kernel.org; Fri, 12 Feb 2021 04:26:58 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:52398) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lAUhb-0001Ck-2y for qemu-devel@nongnu.org; Fri, 12 Feb 2021 04:25:28 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:24738) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lAUhU-0005tl-S4 for qemu-devel@nongnu.org; Fri, 12 Feb 2021 04:25:26 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613121919; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=G13VzGXrnKdWIPnPRY74DAhH7rgNtWPYpG7JwtSviIU=; b=i3rUCGqC+zJb+LbJkZHEnO+q4TkC9rlMNUVWDDbYWHsuycyjRyY6QtOKWE5XANq5s4uw9x 9wD0IDQ/WuDBheJT20xZddR6IP785w5+FY7W7vANeewzkzK1UrEg1Qap/8yY39fRHRrILp 68ufxorNjbTegFgnuROlRucwi8/OKxE= 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-524-RLjJCbRFO9esuqlzH9V_MQ-1; Fri, 12 Feb 2021 04:25:16 -0500 X-MC-Unique: RLjJCbRFO9esuqlzH9V_MQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1F80DDF8A4; Fri, 12 Feb 2021 09:25:15 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-114-227.ams2.redhat.com [10.36.114.227]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D0B281A879; Fri, 12 Feb 2021 09:25:13 +0000 (UTC) Subject: Re: [PATCH 2/2] file-posix: Cache next hole To: Eric Blake , qemu-block@nongnu.org References: <20210211172242.146671-1-mreitz@redhat.com> <20210211172242.146671-3-mreitz@redhat.com> From: Max Reitz Message-ID: <176f890a-5df5-2e68-c29c-b22d312bf977@redhat.com> Date: Fri, 12 Feb 2021 10:25:12 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.569, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.119, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no 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: Kevin Wolf , Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 11.02.21 21:00, Eric Blake wrote: > On 2/11/21 11:22 AM, Max Reitz wrote: >> We have repeatedly received reports that SEEK_HOLE and SEEK_DATA are >> slow on certain filesystems and/or under certain circumstances. That is >> why we generally try to avoid it (which is why bdrv_co_block_status() >> has the @want_zero parameter, and which is why qcow2 has a metadata >> preallocation detection, so we do not fall through to the protocol layer >> to discover which blocks are zero, unless that is really necessary >> (i.e., for metadata-preallocated images)). >> >> In addition to those measures, we can also try to speed up zero >> detection by letting file-posix cache some hole location information, >> namely where the next hole after the most recently queried offset is. >> This helps especially for images that are (nearly) fully allocated, >> which is coincidentally also the case where querying for zero >> information cannot gain us much. >> >> Note that this of course only works so long as we have no concurrent >> writers to the image, which is the case when the WRITE capability is not >> shared. >> >> Alternatively (or perhaps as an improvement in the future), we could let >> file-posix keep track of what it knows is zero and what it knows is >> non-zero with bitmaps, which would help images that actually have a >> significant number of holes (where this implementation here cannot do >> much). But for such images, SEEK_HOLE/DATA are generally faster (they >> do not need to seek through the whole file), and the performance lost by >> querying the block status does not feel as bad because it is outweighed >> by the performance that can be saved by special-cases zeroed areas, so >> focussing on images that are (nearly) fully allocated is more important. > > focusing Wiktionary lists both as valid. *shrug* >> >> Signed-off-by: Max Reitz >> --- >> block/file-posix.c | 81 +++++++++++++++++++++++++++++++++++++++++++++- >> 1 file changed, 80 insertions(+), 1 deletion(-) >> > >> static int find_allocation(BlockDriverState *bs, off_t start, >> off_t *data, off_t *hole) >> { >> -#if defined SEEK_HOLE && defined SEEK_DATA >> BDRVRawState *s = bs->opaque; >> + >> + if (s->next_zero_offset_valid) { >> + if (start >= s->next_zero_offset_from && start < s->next_zero_offset) { >> + *data = start; >> + *hole = s->next_zero_offset; >> + return 0; >> + } >> + } >> + >> +#if defined SEEK_HOLE && defined SEEK_DATA > > Why move the #if? If SEEK_HOLE is not defined, s->next_zero_offset_valid > should never be set, because we'll treat the entire image as data. But > at the same time, it doesn't hurt, so doesn't stop my review. I found it better to put it outside the SEEK_HOLE/DATA section, because while it won’t work when neither are defined, the code is still valid. I don’t know. :) > Reviewed-by: Eric Blake Thanks! Max