Commit 04f315a7 authored by Breno Leitao's avatar Breno Leitao Committed by Andrew Morton
Browse files

mm: remove misleading 'unlikely' hint in vms_gather_munmap_vmas() 

Performance analysis using branch annotation on a fleet of 200 hosts
running web servers revealed that the 'unlikely' hint in
vms_gather_munmap_vmas() was 100% consistently incorrect.  In all observed
cases, the branch behavior contradicted the hint.

Remove the 'unlikely' qualifier from the condition checking 'vms->uf'.  By
doing so, we allow the compiler to make optimization decisions based on
its own heuristics and profiling data, rather than relying on a static
hint that has proven to be inaccurate in real-world scenarios.

Link: https://lkml.kernel.org/r/20241004164832.218681-1-leitao@debian.org


Signed-off-by: default avatarBreno Leitao <leitao@debian.org>
Reviewed-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reviewed-by: default avatarLiam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent b314e215

mm/vma.c

+1 −1
Original line number Diff line number Diff line
@@ -1254,7 +1254,7 @@ int vms_gather_munmap_vmas(struct vma_munmap_struct *vms, 
		else if (is_data_mapping(next->vm_flags))

			vms->data_vm += nrpages;



		if (unlikely(vms->uf)) {

		if (vms->uf) {

			/*

			 * If userfaultfd_unmap_prep returns an error the vmas

			 * will remain split, but userland will get a