** Tags added: cscc
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https://bugs.launchpad.net/bugs/1792102
Title:
Ubuntu18.04: GPU total memory is reduced
Status in The Ubuntu-power-systems project:
Fix Released
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Bionic:
Fix Released
Bug description:
== SRU Justification ==
Due to a recent change for powernv, now the total GPU memory is no longer
available. This impacts performance for any application/benchmark has a
large GPU memory utilization.
IBM is requesting mainlien commit 7acf50e4efa6 in Bionic, which reverts
mainline commit 4b5d62ca17a1.
== Fix ==
7acf50e4efa6 ("Revert "powerpc/powernv: Increase memory block size to 1GB on
radix"")
== Regression Potential ==
Low. This is a revert that was also done upstream due to a regression.
Limited to powerpc.
== Test Case ==
A test kernel was built with this patch and tested by the original bug
reporter.
The bug reporter states the test kernel resolved the bug.
== Comment: #0 - Michael Ranweiler <[email protected]> - 2018-09-10
19:26:14 ==
Due to a recent change for powernv, now the total GPU memory is no
longer available. This impacts performance for any
application/benchmark has a large GPU memory utilization.
Previous amount of memory : 16128MiB
Current amount of available memory : 15360MiB
From Anton, describing the recent change.:
powerpc/powernv: Increase memory block size to 1GB on radix
Memory hot unplug on PowerNV radix hosts is broken. Our memory block
size is 256MB but since we map the linear region with very large
pages, each pte we tear down maps 1GB.
A hot unplug of one 256MB memory block results in 768MB of memory
getting unintentionally unmapped. At this point we are likely to oops.
Fix this by increasing our memory block size to 1GB on PowerNV radix
hosts.
Fixes: 4b5d62ca17a1 ("powerpc/mm: add
radix__remove_section_mapping()")
This is fixed with:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7acf50e4efa6
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