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=-3.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 03CF8C433DF for ; Tue, 19 May 2020 12:54:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D6BC420823 for ; Tue, 19 May 2020 12:54:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="bkIweTKF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726976AbgESMym (ORCPT ); Tue, 19 May 2020 08:54:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41814 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726169AbgESMym (ORCPT ); Tue, 19 May 2020 08:54:42 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 003FFC08C5C0 for ; Tue, 19 May 2020 05:54:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=V9zYkvgQTdQwczYreKhhWQfjcLTB+aruaTifqHrjKc0=; b=bkIweTKFJS/HPIxc7dNaAGqxwE 2AURQrxHIxOaicQgxFxGOkzIC+omSknUoEft8lB/82KLM/j1iCChAJWY5YGCk5hG0cnrGIGK3mxJc tHHi0IXtefydNGq6zL8CriI6VygpkMxq6B9CJPIy6BWk5bWkRpKOGHJtkaecafxbS/KgHynkByNhX PVQEeyzD+Y+weah9d4qeKKkW371SMD+8BQZewC+h6Uqz/PZaXRdmh3DLQXANOBKL4V8O+Tlu4OVe3 clKI4n7GY7vucciMepYBc59YtnEsUNfQbaCaIY489v8H+NQy4FRDV4BLuTJmZ6YYAPAR/J2Qet6JD p2CpcHFg==; Received: from hch by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jb1lV-0004G6-2F; Tue, 19 May 2020 12:54:37 +0000 Date: Tue, 19 May 2020 05:54:37 -0700 From: Christoph Hellwig To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org, hch@infradead.org, bfoster@redhat.com Subject: Re: [PATCH 3/3] xfs: measure all contiguous previous extents for prealloc size Message-ID: <20200519125437.GA15081@infradead.org> References: <158984934500.619853.3585969653869086436.stgit@magnolia> <158984936387.619853.12262802837092587871.stgit@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <158984936387.619853.12262802837092587871.stgit@magnolia> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org The actual logic looks good, but I think the new helper and another third set of comment explaining what is going on makes this area even more confusing. What about something like this instead? diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c index bb590a267a7f9..26f9874361cd3 100644 --- a/fs/xfs/xfs_iomap.c +++ b/fs/xfs/xfs_iomap.c @@ -352,22 +352,10 @@ xfs_quota_calc_throttle( } /* - * If we are doing a write at the end of the file and there are no allocations - * past this one, then extend the allocation out to the file system's write - * iosize. - * * If we don't have a user specified preallocation size, dynamically increase * the preallocation size as the size of the file grows. Cap the maximum size * at a single extent or less if the filesystem is near full. The closer the - * filesystem is to full, the smaller the maximum prealocation. - * - * As an exception we don't do any preallocation at all if the file is smaller - * than the minimum preallocation and we are using the default dynamic - * preallocation scheme, as it is likely this is the only write to the file that - * is going to be done. - * - * We clean up any extra space left over when the file is closed in - * xfs_inactive(). + * filesystem is to full, the smaller the maximum preallocation. */ STATIC xfs_fsblock_t xfs_iomap_prealloc_size( @@ -380,52 +368,58 @@ xfs_iomap_prealloc_size( struct xfs_mount *mp = ip->i_mount; struct xfs_ifork *ifp = XFS_IFORK_PTR(ip, whichfork); xfs_fileoff_t offset_fsb = XFS_B_TO_FSBT(mp, offset); - struct xfs_bmbt_irec prev; + struct xfs_iext_cursor ncur = *icur; + struct xfs_bmbt_irec prev, got; int shift = 0; int64_t freesp; xfs_fsblock_t qblocks; int qshift = 0; - xfs_fsblock_t alloc_blocks = 0; + xfs_fsblock_t alloc_blocks; + xfs_extlen_t plen; - if (offset + count <= XFS_ISIZE(ip)) - return 0; - - if (!(mp->m_flags & XFS_MOUNT_ALLOCSIZE) && - (XFS_ISIZE(ip) < XFS_FSB_TO_B(mp, mp->m_allocsize_blocks))) + /* + * As an exception we don't do any preallocation at all if the file is + * smaller than the minimum preallocation and we are using the default + * dynamic preallocation scheme, as it is likely this is the only write + * to the file that is going to be done. + */ + if (XFS_ISIZE(ip) < XFS_FSB_TO_B(mp, mp->m_allocsize_blocks)) return 0; /* - * If an explicit allocsize is set, the file is small, or we - * are writing behind a hole, then use the minimum prealloc: + * Otherwise use the minimum prealloca size for small files, or if we + * are writing right after a hole. */ - if ((mp->m_flags & XFS_MOUNT_ALLOCSIZE) || - XFS_ISIZE(ip) < XFS_FSB_TO_B(mp, mp->m_dalign) || - !xfs_iext_peek_prev_extent(ifp, icur, &prev) || + if (XFS_ISIZE(ip) < XFS_FSB_TO_B(mp, mp->m_dalign) || + !xfs_iext_prev_extent(ifp, &ncur, &prev) || prev.br_startoff + prev.br_blockcount < offset_fsb) return mp->m_allocsize_blocks; /* - * Determine the initial size of the preallocation. We are beyond the - * current EOF here, but we need to take into account whether this is - * a sparse write or an extending write when determining the - * preallocation size. Hence we need to look up the extent that ends - * at the current write offset and use the result to determine the - * preallocation size. - * - * If the extent is a hole, then preallocation is essentially disabled. - * Otherwise we take the size of the preceding data extent as the basis - * for the preallocation size. If the size of the extent is greater than - * half the maximum extent length, then use the current offset as the - * basis. This ensures that for large files the preallocation size - * always extends to MAXEXTLEN rather than falling short due to things - * like stripe unit/width alignment of real extents. + * Take the size of the contiguous preceding data extents as the basis + * for the preallocation size. Note that we don't care if the previous + * extents are written or not. */ - if (prev.br_blockcount <= (MAXEXTLEN >> 1)) - alloc_blocks = prev.br_blockcount << 1; - else + plen = prev.br_blockcount; + while (xfs_iext_prev_extent(ifp, &ncur, &got)) { + if (plen > MAXEXTLEN / 2 || + got.br_startoff + got.br_blockcount != prev.br_startoff || + got.br_startblock + got.br_blockcount != prev.br_startblock) + break; + plen += got.br_blockcount; + prev = got; + } + + /* + * If the size of the extents is greater than half the maximum extent + * length, then use the current offset as the basis. This ensures that + * for large files the preallocation size always extends to MAXEXTLEN + * rather than falling short due to things like stripe unit/width + * alignment of real extents. + */ + alloc_blocks = plen * 2; + if (alloc_blocks > MAXEXTLEN) alloc_blocks = XFS_B_TO_FSB(mp, offset); - if (!alloc_blocks) - goto check_writeio; qblocks = alloc_blocks; /* @@ -494,7 +488,6 @@ xfs_iomap_prealloc_size( */ while (alloc_blocks && alloc_blocks >= freesp) alloc_blocks >>= 4; -check_writeio: if (alloc_blocks < mp->m_allocsize_blocks) alloc_blocks = mp->m_allocsize_blocks; trace_xfs_iomap_prealloc_size(ip, alloc_blocks, shift, @@ -961,9 +954,16 @@ xfs_buffered_write_iomap_begin( if (error) goto out_unlock; - if (eof) { - prealloc_blocks = xfs_iomap_prealloc_size(ip, allocfork, offset, - count, &icur); + if (eof && offset + count > XFS_ISIZE(ip)) { + /* + * Determine the initial size of the preallocation. + * We clean up any extra preallocation when the file is closed. + */ + if (mp->m_flags & XFS_MOUNT_ALLOCSIZE) + prealloc_blocks = mp->m_allocsize_blocks; + else + prealloc_blocks = xfs_iomap_prealloc_size(ip, allocfork, + offset, count, &icur); if (prealloc_blocks) { xfs_extlen_t align; xfs_off_t end_offset;