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

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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: Breno Leitao <leitao@debian.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Breno Leitao 2024-10-04 09:48:31 -07:00 committed by Andrew Morton
parent b314e21596
commit 04f315a7dc
1 changed files with 1 additions and 1 deletions
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2
mm/vma.c
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@ -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