[lustre-devel] Request arc buffer, zerocopy
Anna Fuchs
anna.fuchs at informatik.uni-hamburg.de
Thu Jun 13 04:54:47 PDT 2019
Dear all,
in osd-zfs/osd_io.c:osd_bufs_get_write you can find a comment regarding
zerocopy:
/*
* currently only full blocks are subject to zerocopy approach:
* so that we're sure nobody is trying to update the same block
*/
Whenever a block to be written is full, an arc buffer is requested,
otherwise alloc_page.
I do not really understand the conclusion. Why and how do full blocks
prevent updates?
And put it differently - why not to try zerocopy for not full blocks?
What could happen if I tried to request an arc buffer for e.g. a block
with missing last page?
I would be greateful for details.
Best regards
Anna
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