c84670950a
Many FreeBSD disk drivers support "unmapped" I/O mode, when data buffer represented not with a virtually contiguous KVA-mapped address range, but with a list of physical memory pages. Originally it was designed to do I/O from buffers without KVA mapping (unmapped). But moving virtual addresses out of equation allows us to operate even non-contiguous data buffers with one condition: all buffer discon- tinuities must be aligned to memory page borders. Doing I/O to capable GEOM device this patch traverses through non- linear ABD buffers, validating the chunks borders. If the condition is met, it supplies GEOM with the list of original physical memory pages instead of copying the data into temporary contiguous buffer. On capable hardware on pools with ashift=12 and default ABD chunk of 4KB it should handle all the I/O without additional memory copying. Reviewed-by: Brian Atkinson <batkinson@lanl.gov> Reviewed-by: Ryan Moeller <ryan@iXsystems.com> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Closes #12320 |
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