padata: remove exit routine

Patch series "padata: parallelize deferred page init", v3.

Deferred struct page init is a bottleneck in kernel boot--the biggest for
us and probably others.  Optimizing it maximizes availability for
large-memory systems and allows spinning up short-lived VMs as needed
without having to leave them running.  It also benefits bare metal
machines hosting VMs that are sensitive to downtime.  In projects such as
VMM Fast Restart[1], where guest state is preserved across kexec reboot,
it helps prevent application and network timeouts in the guests.

So, multithread deferred init to take full advantage of system memory
bandwidth.

Extend padata, a framework that handles many parallel singlethreaded jobs,
to handle multithreaded jobs as well by adding support for splitting up
the work evenly, specifying a minimum amount of work that's appropriate
for one helper thread to do, load balancing between helpers, and
coordinating them.  More documentation in patches 4 and 8.

This series is the first step in a project to address other memory
proportional bottlenecks in the kernel such as pmem struct page init, vfio
page pinning, hugetlb fallocate, and munmap.  Deferred page init doesn't
require concurrency limits, resource control, or priority adjustments like
these other users will because it happens during boot when the system is
otherwise idle and waiting for page init to finish.

This has been run on a variety of x86 systems and speeds up kernel boot by
4% to 49%, saving up to 1.6 out of 4 seconds.  Patch 6 has more numbers.

This patch (of 8):

padata_driver_exit() is unnecessary because padata isn't built as a module
and doesn't exit.

padata's init routine will soon allocate memory, so getting rid of the
exit function now avoids pointless code to free it.

Signed-off-by: Daniel Jordan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Tested-by: Josh Triplett <[email protected]>
Cc: Alexander Duyck <[email protected]>
Cc: Alex Williamson <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Herbert Xu <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Kirill Tkhai <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Pavel Machek <[email protected]>
Cc: Pavel Tatashin <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Robert Elliott <[email protected]>
Cc: Shile Zhang <[email protected]>
Cc: Steffen Klassert <[email protected]>
Cc: Steven Sistare <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Zi Yan <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 0 insertions, 6 deletions

diff --git a/kernel/padata.c b/kernel/padata.c
index aae789896616..b4c7e3e38a05 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -1074,10 +1074,4 @@ static __init int padata_driver_init(void)
 }
 module_init(padata_driver_init);
 
-static __exit void padata_driver_exit(void)
-{
-	cpuhp_remove_multi_state(CPUHP_PADATA_DEAD);
-	cpuhp_remove_multi_state(hp_online);
-}
-module_exit(padata_driver_exit);
 #endif