ZFS big write performance hit upgrading from 2.1.4 to 2.1.5 or 2.1.6 #14009
Comments
ryao
added
Type: Regression
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Would you try ZFS master via the 9999 ebuild and see if the issue is present there too? As long as you do not run a zpool upgrade $pool command, it should be safe to go to ZFS master and then back to 2.1.4. |
Actually, you can. You could clone the official gentoo repo from https://gitweb.gentoo.org/repo/gentoo.git/ |
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@satarsa thanks for that. And @ryao I connected with one of the Gentoo maintainers for ZFS offline, and he provided me with some instructions on how to use the 9999 ebuild along with bisecting between 2.1.4 and 2.1.5. I’m happy to try and find the commit where the perf regression showed up, at least for my ZFS setup. I honestly didn’t think this would get so much activity though shortly after I opened the issue! I’m currently not at home where this server is, but I’ll try and run some of these bisect ops while I’m away this week. Worst case, I can get this nailed down this coming weekend. All of the support is greatly appreciated!! |
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I did not expect you to bisect it, but if you do, that would be awesome. I should be able to figure this out quickly if you identify the bad patch through a bisect. |
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I haven’t started bisecting yet, but more info on my system/setup where I’m seeing this issue:
So I do have many cores in the system running. In that RAIDz3 pool, I have many datasets carved out, where I’m pushing about 31TB used total. Most of it is video-based streaming content for Plex, so not lots of tiny files. I hope to have more info once I can coordinate with home and bisect on the live system. |
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Apologies for the delay on this. I was finally able to get some time on the box and bisect this. This is the offending commit that is killing write performance on my system: I've taken this a step further and while on the build with this patch, I turned off that tunable:
And then re-tested immediately after. The issue went away. I went from about 100kB/sec write performance to 150MB/sec (note the order of magnitude difference). UPDATE: I went ahead and built the 2.1.6 ebuilds, and confirmed I still had this issue. I then turned off the same tunable, and the performance issue went away. Hope this helps inform how to deal with this upstream. |
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Nice find. |
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I should warn you, turning that off will result in sometimes treating files as dense when they're sparse if that hasn't synced out yet, IIRC, so if that's a use case you care about, you may be sad. Of course, when you're handing it to ZFS with compression on, it'll eat the sparseness one way or another, it's just a question of whether you unnecessarily copied some zeroes only to throw them out, so, if this works for you, great, just be aware that it results in additional IO overhead if you come looking for performance bottlenecks again. |
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I see it not great to allow regular unprivileged user to force or depend on pool TXG commits. There should be some better solution. |
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I think at very least the code could be optimized to not even think to commit TXG if file is below a certain size, especially if below one block, that means it can't have holes unless it is a one big hole. If I understood right and the workload is updating Linux source tree, then I guess most/many of source files should fit within one block. |
`lseek(SEEK_DATA | SEEK_HOLE)` are only accurate when the on-disk blocks reflect all writes, i.e. when there are no dirty data blocks. To ensure this, if the target dnode is dirty, they wait for the open txg to be synced, so we can call them "stabilizing operations". If they cause txg_wait_synced often, it can be detrimental to performance. Typically, a group of files are all modified, and then SEEK_DATA/HOLE are performed on them. In this case, the first SEEK does a txg_wait_synced(), and subsequent SEEKs don't need to wait, so performance is good. However, if a workload involves an interleaved metadata modification, the subsequent SEEK may do a txg_wait_synced() unnecessarily. For example, if we do a `read()` syscall to each file before we do its SEEK. This applies even with `relatime=on`, when the `read()` is the first read after the last write. The txg_wait_synced() is unnecessary because the SEEK operations only care that the structure of the tree of indirect and data blocks is up to date on disk. They don't care about metadata like the contents of the bonus or spill blocks. (They also don't care if an existing data block is modified, but this would be more involved to filter out.) This commit changes the behavior of SEEK_DATA/HOLE operations such that they do not call txg_wait_synced() if there is only a pending change to the bonus or spill block. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Matthew Ahrens <mahrens@delphix.com> Closes #13368 Issue #14594 Issue #14512 Issue #14009
`lseek(SEEK_DATA | SEEK_HOLE)` are only accurate when the on-disk blocks reflect all writes, i.e. when there are no dirty data blocks. To ensure this, if the target dnode is dirty, they wait for the open txg to be synced, so we can call them "stabilizing operations". If they cause txg_wait_synced often, it can be detrimental to performance. Typically, a group of files are all modified, and then SEEK_DATA/HOLE are performed on them. In this case, the first SEEK does a txg_wait_synced(), and subsequent SEEKs don't need to wait, so performance is good. However, if a workload involves an interleaved metadata modification, the subsequent SEEK may do a txg_wait_synced() unnecessarily. For example, if we do a `read()` syscall to each file before we do its SEEK. This applies even with `relatime=on`, when the `read()` is the first read after the last write. The txg_wait_synced() is unnecessary because the SEEK operations only care that the structure of the tree of indirect and data blocks is up to date on disk. They don't care about metadata like the contents of the bonus or spill blocks. (They also don't care if an existing data block is modified, but this would be more involved to filter out.) This commit changes the behavior of SEEK_DATA/HOLE operations such that they do not call txg_wait_synced() if there is only a pending change to the bonus or spill block. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Matthew Ahrens <mahrens@delphix.com> Closes openzfs#13368 Issue openzfs#14594 Issue openzfs#14512 Issue openzfs#14009
`lseek(SEEK_DATA | SEEK_HOLE)` are only accurate when the on-disk blocks reflect all writes, i.e. when there are no dirty data blocks. To ensure this, if the target dnode is dirty, they wait for the open txg to be synced, so we can call them "stabilizing operations". If they cause txg_wait_synced often, it can be detrimental to performance. Typically, a group of files are all modified, and then SEEK_DATA/HOLE are performed on them. In this case, the first SEEK does a txg_wait_synced(), and subsequent SEEKs don't need to wait, so performance is good. However, if a workload involves an interleaved metadata modification, the subsequent SEEK may do a txg_wait_synced() unnecessarily. For example, if we do a `read()` syscall to each file before we do its SEEK. This applies even with `relatime=on`, when the `read()` is the first read after the last write. The txg_wait_synced() is unnecessary because the SEEK operations only care that the structure of the tree of indirect and data blocks is up to date on disk. They don't care about metadata like the contents of the bonus or spill blocks. (They also don't care if an existing data block is modified, but this would be more involved to filter out.) This commit changes the behavior of SEEK_DATA/HOLE operations such that they do not call txg_wait_synced() if there is only a pending change to the bonus or spill block. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Matthew Ahrens <mahrens@delphix.com> Closes #13368 Issue #14594 Issue #14512 Issue #14009
`lseek(SEEK_DATA | SEEK_HOLE)` are only accurate when the on-disk blocks reflect all writes, i.e. when there are no dirty data blocks. To ensure this, if the target dnode is dirty, they wait for the open txg to be synced, so we can call them "stabilizing operations". If they cause txg_wait_synced often, it can be detrimental to performance. Typically, a group of files are all modified, and then SEEK_DATA/HOLE are performed on them. In this case, the first SEEK does a txg_wait_synced(), and subsequent SEEKs don't need to wait, so performance is good. However, if a workload involves an interleaved metadata modification, the subsequent SEEK may do a txg_wait_synced() unnecessarily. For example, if we do a `read()` syscall to each file before we do its SEEK. This applies even with `relatime=on`, when the `read()` is the first read after the last write. The txg_wait_synced() is unnecessary because the SEEK operations only care that the structure of the tree of indirect and data blocks is up to date on disk. They don't care about metadata like the contents of the bonus or spill blocks. (They also don't care if an existing data block is modified, but this would be more involved to filter out.) This commit changes the behavior of SEEK_DATA/HOLE operations such that they do not call txg_wait_synced() if there is only a pending change to the bonus or spill block. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Matthew Ahrens <mahrens@delphix.com> Closes openzfs#13368 Issue openzfs#14594 Issue openzfs#14512 Issue openzfs#14009
`lseek(SEEK_DATA | SEEK_HOLE)` are only accurate when the on-disk blocks reflect all writes, i.e. when there are no dirty data blocks. To ensure this, if the target dnode is dirty, they wait for the open txg to be synced, so we can call them "stabilizing operations". If they cause txg_wait_synced often, it can be detrimental to performance. Typically, a group of files are all modified, and then SEEK_DATA/HOLE are performed on them. In this case, the first SEEK does a txg_wait_synced(), and subsequent SEEKs don't need to wait, so performance is good. However, if a workload involves an interleaved metadata modification, the subsequent SEEK may do a txg_wait_synced() unnecessarily. For example, if we do a `read()` syscall to each file before we do its SEEK. This applies even with `relatime=on`, when the `read()` is the first read after the last write. The txg_wait_synced() is unnecessary because the SEEK operations only care that the structure of the tree of indirect and data blocks is up to date on disk. They don't care about metadata like the contents of the bonus or spill blocks. (They also don't care if an existing data block is modified, but this would be more involved to filter out.) This commit changes the behavior of SEEK_DATA/HOLE operations such that they do not call txg_wait_synced() if there is only a pending change to the bonus or spill block. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Matthew Ahrens <mahrens@delphix.com> Closes openzfs#13368 Issue openzfs#14594 Issue openzfs#14512 Issue openzfs#14009
`lseek(SEEK_DATA | SEEK_HOLE)` are only accurate when the on-disk blocks reflect all writes, i.e. when there are no dirty data blocks. To ensure this, if the target dnode is dirty, they wait for the open txg to be synced, so we can call them "stabilizing operations". If they cause txg_wait_synced often, it can be detrimental to performance. Typically, a group of files are all modified, and then SEEK_DATA/HOLE are performed on them. In this case, the first SEEK does a txg_wait_synced(), and subsequent SEEKs don't need to wait, so performance is good. However, if a workload involves an interleaved metadata modification, the subsequent SEEK may do a txg_wait_synced() unnecessarily. For example, if we do a `read()` syscall to each file before we do its SEEK. This applies even with `relatime=on`, when the `read()` is the first read after the last write. The txg_wait_synced() is unnecessary because the SEEK operations only care that the structure of the tree of indirect and data blocks is up to date on disk. They don't care about metadata like the contents of the bonus or spill blocks. (They also don't care if an existing data block is modified, but this would be more involved to filter out.) This commit changes the behavior of SEEK_DATA/HOLE operations such that they do not call txg_wait_synced() if there is only a pending change to the bonus or spill block. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Matthew Ahrens <mahrens@delphix.com> Closes openzfs#13368 Issue openzfs#14594 Issue openzfs#14512 Issue openzfs#14009
`lseek(SEEK_DATA | SEEK_HOLE)` are only accurate when the on-disk blocks reflect all writes, i.e. when there are no dirty data blocks. To ensure this, if the target dnode is dirty, they wait for the open txg to be synced, so we can call them "stabilizing operations". If they cause txg_wait_synced often, it can be detrimental to performance. Typically, a group of files are all modified, and then SEEK_DATA/HOLE are performed on them. In this case, the first SEEK does a txg_wait_synced(), and subsequent SEEKs don't need to wait, so performance is good. However, if a workload involves an interleaved metadata modification, the subsequent SEEK may do a txg_wait_synced() unnecessarily. For example, if we do a `read()` syscall to each file before we do its SEEK. This applies even with `relatime=on`, when the `read()` is the first read after the last write. The txg_wait_synced() is unnecessary because the SEEK operations only care that the structure of the tree of indirect and data blocks is up to date on disk. They don't care about metadata like the contents of the bonus or spill blocks. (They also don't care if an existing data block is modified, but this would be more involved to filter out.) This commit changes the behavior of SEEK_DATA/HOLE operations such that they do not call txg_wait_synced() if there is only a pending change to the bonus or spill block. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Matthew Ahrens <mahrens@delphix.com> Closes openzfs#13368 Issue openzfs#14594 Issue openzfs#14512 Issue openzfs#14009
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System information
Describe the problem you're observing
I've been running ZFS 2.1.4 for quite some time on my main ZFS array, using RAIDz3 with a very large dataset (85TB online). On Gentoo, I can only run a 5.15.x or lower kernel with this version. Upgrading to a 5.18 or 5.19 kernel, I need to upgrade to use ZFS 2.1.6 to compile for the newer kernel. When I try this, my write performance goes from 100-150MB/sec of write on 5.15 and ZFS 2.1.4 (testing emerge -a =sys-kernel/gentoo-sources-5.10.144) to about 100 kB/sec on 5.19.14 and ZFS 2.1.6.
I've tried ZFS 2.1.5 and 2.1.6 with a 5.15.72 kernel, and had the exact same performance regression.
The big issue is ZFS 2.1.4 has now been removed from the main world list after an emerge --sync, so I can't revert my installed version of 2.1.6.
Describe how to reproduce the problem
Upgrade an existing host to ZFS 2.1.5 or 2.1.6, attempt writing a larger package with lots of smaller files (e.g. a Linux kernel source package) and observe the write performance reduced by a factor of about 100.
Include any warning/errors/backtraces from the system logs
I see nothing indicating anything is going wrong. Nothing in dmesg, nothing in syslogs, and zpool status is clean.
Rebooting into a 5.15 kernel with ZFS 2.1.4 on the exact same array returns the expected performance.
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