[0/4] brd: implement discard

Message

Mikulas Patocka Sept. 16, 2022, 8:58 a.m. UTC

Hi

This series of patches implements discard, write_zeroes and secure_erase 
support for the brd driver.

Zdenek asked me to write it, because we use brd in the lvm2 testsuite and 
it would be benefical to run the testsuite with discard enabled in order 
to test discard handling.

This patch series should have no performance impact - it doesn't add any 
locks to the common I/O paths. It only extends rcu read region around 
lookup and reading or writing of a single page. Discarded pages are freed 
with "call_rcu" to make sure that if we mix discard with I/O, the I/O 
won't access freed memory.

Mikulas