ARC: Remove b_bufcnt/b_ebufcnt from ARC headers #15350
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This was referenced Oct 4, 2023
In most cases we do not care about exact number of buffers linked to the header, we just need to know if it is zero, non-zero or one. That can easily be checked just looking on b_buf pointer or in some cases derefencing it. b_ebufcnt is read only once, and in that case we already traverse the list as part of arc_buf_remove(), so second traverse should not be expensive. This reduces L1 ARC header size by 8 bytes and full crypto header by 16 bytes, down to 176 and 232 bytes on FreeBSD respectively. Signed-off-by: Alexander Motin <[email protected]> Sponsored by: iXsystems, Inc.
amotin
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I was able to save additional 8 bytes on removing also b_ebufcnt. |
behlendorf
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Oct 6, 2023
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Status: Accepted
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Oct 6, 2023
In most cases we do not care about exact number of buffers linked to the header, we just need to know if it is zero, non-zero or one. That can easily be checked just looking on b_buf pointer or in some cases derefencing it. b_ebufcnt is read only once, and in that case we already traverse the list as part of arc_buf_remove(), so second traverse should not be expensive. This reduces L1 ARC header size by 8 bytes and full crypto header by 16 bytes, down to 176 and 232 bytes on FreeBSD respectively. Reviewed-by: Brian Behlendorf <[email protected]> Signed-off-by: Alexander Motin <[email protected]> Sponsored by: iXsystems, Inc. Closes openzfs#15350
behlendorf
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Oct 7, 2023
In most cases we do not care about exact number of buffers linked to the header, we just need to know if it is zero, non-zero or one. That can easily be checked just looking on b_buf pointer or in some cases derefencing it. b_ebufcnt is read only once, and in that case we already traverse the list as part of arc_buf_remove(), so second traverse should not be expensive. This reduces L1 ARC header size by 8 bytes and full crypto header by 16 bytes, down to 176 and 232 bytes on FreeBSD respectively. Reviewed-by: Brian Behlendorf <[email protected]> Signed-off-by: Alexander Motin <[email protected]> Sponsored by: iXsystems, Inc. Closes #15350
lundman
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Dec 12, 2023
In most cases we do not care about exact number of buffers linked to the header, we just need to know if it is zero, non-zero or one. That can easily be checked just looking on b_buf pointer or in some cases derefencing it. b_ebufcnt is read only once, and in that case we already traverse the list as part of arc_buf_remove(), so second traverse should not be expensive. This reduces L1 ARC header size by 8 bytes and full crypto header by 16 bytes, down to 176 and 232 bytes on FreeBSD respectively. Reviewed-by: Brian Behlendorf <[email protected]> Signed-off-by: Alexander Motin <[email protected]> Sponsored by: iXsystems, Inc. Closes openzfs#15350
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In most cases we do not care about exact number of buffers linked to the header, we just need to know if it is zero, non-zero or one. That can easily be checked just looking on b_buf pointer or in some cases derefencing it.
b_ebufcnt is read only once, and in that case we already traverse the list as part of arc_buf_remove(), so second traverse should not be expensive.
This reduces L1 ARC header size by 8 bytes and full crypto header by 16 bytes, down to 176 and 232 bytes on FreeBSD respectively.
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