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From 9a106b5fbb88342f0ee02891d1bbb0e3c5a93d03 Mon Sep 17 00:00:00 2001
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From: Donald Douwsma <ddouwsma@redhat.com>
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Date: Fri, 15 Sep 2017 08:33:42 -0500
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Subject: [PATCH] mkfs.xfs: Don't stagger AG for a single disk
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When sunit and swidth are used mkfs.xfs tries to avoid all allocation
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groups aligning on the same stripe and will attempt to stagger them
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across the stripes that make up swidth. If there is only one stripe
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then there is no benefit in this optimisation.
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$ truncate -s10G xfs_10G_su256k_sw1.image
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$ mkfs.xfs -d su=256k,sw=1 xfs_10G_su256k_sw1.image
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meta-data=xfs_10G_su256k_sw1.image isize=512 agcount=16, agsize=163776 blks
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= sectsz=512 attr=2, projid32bit=1
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= crc=1 finobt=0, sparse=0
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data = bsize=4096 blocks=2620416, imaxpct=25
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= sunit=64 swidth=64 blks
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naming =version 2 bsize=4096 ascii-ci=0 ftype=1
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log =internal log bsize=4096 blocks=2560, version=2
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= sectsz=512 sunit=64 blks, lazy-count=1
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realtime =none extsz=4096 blocks=0, rtextents=0
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A side effect of the optimisation is that the size adjustment used to stager
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the allocation groups causes the last sunit of storage to be unused.
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$ echo $((2620416*4096))
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10733223936
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$ ls -l xfs_10G_su256k_sw1.image
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-rw-rw-r--. 1 test test 10737418240 Aug 30 10:54 xfs_10G_su256k_sw1.image
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Skip this optimisation when sunit == swidth.
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Signed-off-by: Donald Douwsma <ddouwsma@redhat.com>
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Reviewed-by: Eric Sandeen <sandeen@redhat.com>
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Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
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---
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mkfs/xfs_mkfs.c | 4 +++-
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1 file changed, 3 insertions(+), 1 deletion(-)
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Index: xfsprogs-rhel7.5/mkfs/xfs_mkfs.c
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===================================================================
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--- xfsprogs-rhel7.5.orig/mkfs/xfs_mkfs.c
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+++ xfsprogs-rhel7.5/mkfs/xfs_mkfs.c
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@@ -2308,7 +2308,9 @@ reported by the device (%u).\n"),
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}
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}
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}
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- if (dswidth && ((agsize % dswidth) == 0) && (agcount > 1)) {
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+ if (dswidth && ((agsize % dswidth) == 0)
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+ && (dswidth != dsunit)
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+ && (agcount > 1)) {
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/* This is a non-optimal configuration because all AGs
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* start on the same disk in the stripe. Changing
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* the AG size by one sunit will guarantee that this
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