Use zio buffers in zil_itx_create() #3059
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behlendorf
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Bug - Minor
Type: Performance
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@ryao you might find this interesting. It's also related to the recent kmem changes. If you could review it that would be great. |
behlendorf
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Component: Memory Management
The zil_itx_create() function uses the vmem_alloc() allocator for its buffers because when logging a write that buffer may be as large as 64K. This is non-optimal because we may need to allocate many of of these buffers and this interface has the potential to be slow. Instead, use zio_data_buf_alloc() which is specifically designed to be able to efficiently allocate a wide range of buffer sizes. In addition, do some cleanup and use the zil_itx_destroy() function to always free an itx structure. This way we're always sure the right allocation functions are used. Notice that in the current code kmem_free() and vmem_free() were both used. This happened to work because these wrappers map to the same internal SPL function. This was identified as a potential problem when a low-end memory constrained system began logging the following warnings. There was no deadlock here just repeated allocation failures resulting in increased latency. Possible memory allocation deadlock: size=65792 lflags=0x42d0 Pid: 20118, comm: kvm Tainted: P O 3.2.0-0.bpo.4-amd64 Call Trace: [<ffffffffa040b834>] ? spl_kmem_alloc_impl+0x115/0x127 [spl] [<ffffffffa040b84f>] ? spl_kmem_alloc_debug+0x9/0x36 [spl] [<ffffffffa05d8a0b>] ? zil_itx_create+0x2d/0x59 [zfs] [<ffffffffa05c71e6>] ? zfs_log_write+0x13a/0x2f0 [zfs] [<ffffffffa05d41bc>] ? zfs_write+0x85b/0x9bb [zfs] [<ffffffffa05e37ec>] ? zpl_aio_write+0xca/0x110 [zfs] [<ffffffff811088e5>] ? do_sync_readv_writev+0xa3/0xde [<ffffffff81108f41>] ? do_readv_writev+0xaf/0x125 [<ffffffff81109055>] ? sys_pwritev+0x55/0x9a [<ffffffff813721d2>] ? system_call_fastpath+0x16/0x1b Signed-off-by: Brian Behlendorf <[email protected]>
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The zil_itx_create() function uses the vmem_alloc() allocator for its buffers because when logging a write that buffer may be as large as 64K. This is non-optimal because we may need to allocate many of of these buffers and this interface has the potential to be slow. Instead, use zio_data_buf_alloc() which is specifically designed to be able to efficiently allocate a wide range of buffer sizes. In addition, do some cleanup and use the zil_itx_destroy() function to always free an itx structure. This way we're always sure the right allocation functions are used. Notice that in the current code kmem_free() and vmem_free() were both used. This happened to work because these wrappers map to the same internal SPL function. This was identified as a potential problem when a low-end memory constrained system began logging the following warnings. There was no deadlock here just repeated allocation failures resulting in increased latency. Possible memory allocation deadlock: size=65792 lflags=0x42d0 Pid: 20118, comm: kvm Tainted: P O 3.2.0-0.bpo.4-amd64 Call Trace: [<ffffffffa040b834>] ? spl_kmem_alloc_impl+0x115/0x127 [spl] [<ffffffffa040b84f>] ? spl_kmem_alloc_debug+0x9/0x36 [spl] [<ffffffffa05d8a0b>] ? zil_itx_create+0x2d/0x59 [zfs] [<ffffffffa05c71e6>] ? zfs_log_write+0x13a/0x2f0 [zfs] [<ffffffffa05d41bc>] ? zfs_write+0x85b/0x9bb [zfs] [<ffffffffa05e37ec>] ? zpl_aio_write+0xca/0x110 [zfs] [<ffffffff811088e5>] ? do_sync_readv_writev+0xa3/0xde [<ffffffff81108f41>] ? do_readv_writev+0xaf/0x125 [<ffffffff81109055>] ? sys_pwritev+0x55/0x9a [<ffffffff813721d2>] ? system_call_fastpath+0x16/0x1b Signed-off-by: Brian Behlendorf <[email protected]> Signed-off-by: Richard Yao <[email protected]> Closes openzfs#3059
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The zil_itx_create() function uses the vmem_alloc() allocator for
its buffers because when logging a write that buffer may be as large
as 64K. This is non-optimal because we may need to allocate many of
of these buffers and this interface has the potential to be slow.
Instead, use zio_data_buf_alloc() which is specifically designed to
be able to efficiently allocate a wide range of buffer sizes.
This was identified as a potential problem when a low-end memory
constrained system began logging the following warnings. There
was no deadlock here just repeated allocation failures resulting
in increased latency.
Possible memory allocation deadlock: size=65792 lflags=0x42d0
Pid: 20118, comm: kvm Tainted: P O 3.2.0-0.bpo.4-amd64
Call Trace:
[] ? spl_kmem_alloc_impl+0x115/0x127 [spl]
[] ? spl_kmem_alloc_debug+0x9/0x36 [spl]
[] ? zil_itx_create+0x2d/0x59 [zfs]
[] ? zfs_log_write+0x13a/0x2f0 [zfs]
[] ? zfs_write+0x85b/0x9bb [zfs]
[] ? zpl_aio_write+0xca/0x110 [zfs]
[] ? do_sync_readv_writev+0xa3/0xde
[] ? do_readv_writev+0xaf/0x125
[] ? sys_pwritev+0x55/0x9a
[] ? system_call_fastpath+0x16/0x1b
Signed-off-by: Brian Behlendorf [email protected]