zpool: speed up importing large pools #11469
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The ZFS_IOC_POOL_TRYIMPORT ioctl returns an nvlist from the kernel to a preallocated buffer in userland. Userland must guess how large the buffer should be. If it undersizes it, it must reallocate and try again. That can cost a lot of time for large pools. OpenZFS commit 28b40c8 set the guess at "zc.zc_nvlist_conf_size * 4" without explanation. On my system, that is too small. From experiment, x 32 is a better multiplier. But I don't know how to calculate it theoretically. Sponsored by: Axcient Signed-off-by: Alan Somers <[email protected]>
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asomers
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Jan 19, 2021
The ZFS_IOC_POOL_TRYIMPORT ioctl returns an nvlist from the kernel to a preallocated buffer in userland. Userland must guess how large the buffer should be. If it undersizes it, it must reallocated and try again. That can cost a lot of time for large pools. OpenZFS commit 28b40c8 set the guess at "zc.zc_nvlist_conf_size * 4" without explanation. On my system, that is too small. From experiment, x32 is a better multiplier. But I don't know how to calculate it from theory. openzfs/zfs#11469 Sponsored by: Axcient
alek-p
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Jan 19, 2021
behlendorf
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behlendorf
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Jan 20, 2021
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Status: Accepted
jsai20
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Mar 30, 2021
The ZFS_IOC_POOL_TRYIMPORT ioctl returns an nvlist from the kernel to a preallocated buffer in userland. Userland must guess how large the buffer should be. If it undersizes it, it must reallocate and try again. That can cost a lot of time for large pools. OpenZFS commit 28b40c8 set the guess at "zc.zc_nvlist_conf_size * 4" without explanation. On my system, that is too small. From experiment, x 32 is a better multiplier. But I don't know how to calculate it theoretically. Sponsored by: Axcient Reviewed-by: Brian Behlendorf <[email protected]> Reviewed-by: Alek Pinchuk <[email protected]> Signed-off-by: Alan Somers <[email protected]> Closes openzfs#11469
sempervictus
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May 31, 2021
The ZFS_IOC_POOL_TRYIMPORT ioctl returns an nvlist from the kernel to a preallocated buffer in userland. Userland must guess how large the buffer should be. If it undersizes it, it must reallocate and try again. That can cost a lot of time for large pools. OpenZFS commit 28b40c8 set the guess at "zc.zc_nvlist_conf_size * 4" without explanation. On my system, that is too small. From experiment, x 32 is a better multiplier. But I don't know how to calculate it theoretically. Sponsored by: Axcient Reviewed-by: Brian Behlendorf <[email protected]> Reviewed-by: Alek Pinchuk <[email protected]> Signed-off-by: Alan Somers <[email protected]> Closes openzfs#11469
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Motivation and Context
The ZFS_IOC_POOL_TRYIMPORT ioctl returns an nvlist from the kernel to a
preallocated buffer in userland. Userland must guess how large the
buffer should be. If it undersizes it, it must reallocate and try
again. That can cost a lot of time for large pools.
Description
OpenZFS commit 28b40c8 set the guess at "zc.zc_nvlist_conf_size * 4"
without explanation. On my system, that is too small. From experiment,
x 32 is a better multiplier. But I don't know how to calculate it
theoretically.
Sponsored by: Axcient
Signed-off-by: Alan Somers [email protected]
How Has This Been Tested?
Performance tested on FreeBSD 13 using six various pools of up to 20 top-level vdevs. Regression tested with FreeBSD's ZFS test suite. Reduces the number of
spa_load's during import of large pools by one third. Overall performance improvement forzpool importis about 18% .Types of changes
Checklist:
Signed-off-by.