From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:33012 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755433AbeEHRWc (ORCPT ); Tue, 8 May 2018 13:22:32 -0400 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.24]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CDDD730CB6F4 for ; Tue, 8 May 2018 17:22:32 +0000 (UTC) Received: from bfoster.bfoster (dhcp-41-20.bos.redhat.com [10.18.41.20]) by smtp.corp.redhat.com (Postfix) with ESMTP id B19BB30B36E3 for ; Tue, 8 May 2018 17:22:32 +0000 (UTC) From: Brian Foster Subject: [PATCH v2 3/3] xfs: don't discard on free of unwritten extents Date: Tue, 8 May 2018 13:22:31 -0400 Message-Id: <20180508172231.53570-4-bfoster@redhat.com> In-Reply-To: <20180508172231.53570-1-bfoster@redhat.com> References: <20180508172231.53570-1-bfoster@redhat.com> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: linux-xfs@vger.kernel.org Unwritten extents by definition have not been written to until they are converted to normal written extents. If unwritten extents are freed from a file, it is therefore guaranteed that the blocks have not been written to since allocation (note that zero range punches and reallocates blocks). To cut down on online discards generated from workloads that make use of preallocation, skip discards of extents if they are in the unwritten state when the extent is freed. Note that this optimization does not apply to log recovery, during which all freed extents are discarded if online discard is enabled. Also note that it may be possible for a filesystem crash to occur after write completion of an unwritten extent but before unwritten conversion such that the extent remains unwritten after log recovery. Since this pseudo-inconsistency may already be possible after a crash (consider writing to recently allocated blocks where the allocation transaction is lost after a crash), this change shouldn't introduce any fundamental limitations that don't already exist. In short, on storage stacks where discards are important, it's good practice to run an occasional fstrim even with online discard enabled in the filesystem, particularly after a crash. Signed-off-by: Brian Foster --- fs/xfs/libxfs/xfs_bmap.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c index dfec27b10e7a..24f60ee810e4 100644 --- a/fs/xfs/libxfs/xfs_bmap.c +++ b/fs/xfs/libxfs/xfs_bmap.c @@ -5107,7 +5107,8 @@ xfs_bmap_del_extent_real( if (error) goto done; } else { - if (bflags & XFS_BMAPI_NODISCARD) { + if ((bflags & XFS_BMAPI_NODISCARD) || + (del->br_state == XFS_EXT_UNWRITTEN)) { xfs_bmap_add_free_nodiscard(mp, dfops, del->br_startblock, del->br_blockcount, NULL); -- 2.14.3