On 6/20/19 5:58 PM, Damien Le Moal wrote:
The REPORT_ZONES command is executed using scsi_execute_req(). Can we pass a
vmalloc-ed buffer to that function ? It does look like it since scsi_execute_rq
calls bio_rq_map_kern() which then calls bio_map_kern() which goes through the
list of pages of the buffer. Just would like to confirm I understand this correctly.
My concern with using vmalloc is that the worst case scenario will result in all
pages of the buffer being non contiguous. In this case, since the report zones
command cannot be split, we would need to limit the allocation to max_segments *
page size, and that can be pretty small for some HBAs.
Another reason I did not pursue the vmalloc route is that the processing of the
report zones reply to transform zone information into struct blkzone is really
painful to do with a vmalloced buffer as every page of the buffer needs to be
kmap()/kunmap(). The code was like that when REPORT ZONES was processed as a
BIO/request, but it was a lot of code for not much to be done. Or is there a
more elegant solution for in-kernel mapping of a vmalloc buffer ?
Hi Damien,
I don't think that bio_rq_map_kern() works with vmalloc-ed buffers. How
about using is_vmalloc_addr() inside scsi_execute_req() to determine
whether or not the buffer passed to that function has been allocated
with vmalloc()? There may be other scsi_execute_req() callers that can
benefit from passing a vmalloc-ed buffer to that function.
Regarding the maximum segment size: is mpt3sas still the most popular
HBA? Is the maximum segment size 128 for that driver? Is 128 * 4 KB =
512 KB big enough for the report zones buffer?
Regarding the loop that calls sd_zbc_parse_report(): are you sure that
that kmap()/kunmap() calls would be necessary in that loop?
Thanks,
Bart.
