From: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> Subject: 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. Link: http://lkml.kernel.org/r/20200527173608.2885243-1-daniel.m.jordan@xxxxxxxxxx Link: http://lkml.kernel.org/r/20200527173608.2885243-2-daniel.m.jordan@xxxxxxxxxx Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> Tested-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx> Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> Cc: Jason Gunthorpe <jgg@xxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Pavel Machek <pavel@xxxxxx> Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> Cc: Robert Elliott <elliott@xxxxxxx> Cc: Shile Zhang <shile.zhang@xxxxxxxxxxxxxxxxx> Cc: Steffen Klassert <steffen.klassert@xxxxxxxxxxx> Cc: Steven Sistare <steven.sistare@xxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Cc: Zi Yan <ziy@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/padata.c | 6 ------ 1 file changed, 6 deletions(-) --- a/kernel/padata.c~padata-remove-exit-routine +++ a/kernel/padata.c @@ -1074,10 +1074,4 @@ static __init int padata_driver_init(voi } 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 _
