On 12/6/20 2:32 PM, Tom Yan wrote:
Why? Did you miss that it is in the condition where
__blkdev_issue_zero_pages() is called (i.e. it's not WRITE SAME but
WRITE). From what I gathered REQ_PREFLUSH triggers a write back cache
(that is on the device; not sure about dirty pages) flush, wouldn't it
be a right thing to do after we performed a series of WRITE (which is
more or less purposed to get a drive wiped clean).
But what makes 'zero_pages' special as compared to, say, WRITE_SAME?
One could use WRITE SAME with '0' content, arriving at pretty much the
same content than usine zeroout without unmapping. And neither of them
worries about cache flushing.
Nor should they, IMO.
These are 'native' block layer calls, providing abstract accesses to
hardware functionality. If an application wants to use them, it would be
the task of the application to insert a 'flush' if it deems neccessary.
(There _is_ blkdev_issue_flush(), after all).
Cheers,
Hannes
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Dr. Hannes Reinecke Kernel Storage Architect
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