The patch titled
Subject: mm/mmap: change vma iteration order in do_vmi_align_munmap()
has been added to the -mm mm-unstable branch. Its filename is
mm-mmap-change-vma-iteration-order-in-do_vmi_align_munmap.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mmap-change-vma-iteration-order-in-do_vmi_align_munmap.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
Subject: mm/mmap: change vma iteration order in do_vmi_align_munmap()
Date: Mon, 12 Jun 2023 16:39:53 -0400
By delaying the setting of prev/next VMA until after the write of NULL,
the probability of the prev/next VMA already being in the CPU cache is
significantly increased, especially for larger munmap operations. It also
means that prev/next will be loaded closer to when they are used.
This has the consequence of needing to change the for_each() to a do {}
for_each() when writing to the side tree.
Since prev will be set later in the function, it is better to reverse the
splitting direction of the start VMA (modify the new_below argument to
__split_vma).
Using the vma_iter_prev_range() to walk back to the correct location in
the tree will, on the most part, mean walking within the CPU cache.
Usually, this is two steps vs a node reset and a tree re-walk.
Link: https://lkml.kernel.org/r/20230612203953.2093911-17-Liam.Howlett@xxxxxxxxxx
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mmap.c | 27 ++++++++++++---------------
1 file changed, 12 insertions(+), 15 deletions(-)
--- a/mm/mmap.c~mm-mmap-change-vma-iteration-order-in-do_vmi_align_munmap
+++ a/mm/mmap.c
@@ -2392,20 +2392,17 @@ do_vmi_align_munmap(struct vma_iterator
if (end < vma->vm_end && mm->map_count >= sysctl_max_map_count)
goto map_count_exceeded;
- error = __split_vma(vmi, vma, start, 0);
+ error = __split_vma(vmi, vma, start, 1);
if (error)
goto start_split_failed;
-
- vma = vma_iter_load(vmi);
}
- prev = vma_prev(vmi);
-
/*
* Detach a range of VMAs from the mm. Using next as a temp variable as
* it is always overwritten.
*/
- for_each_vma_range(*vmi, next, end) {
+ next = vma;
+ do {
/* Does it split the end? */
if (next->vm_end > end) {
error = __split_vma(vmi, next, end, 0);
@@ -2422,13 +2419,7 @@ do_vmi_align_munmap(struct vma_iterator
BUG_ON(next->vm_start < start);
BUG_ON(next->vm_start > end);
#endif
- }
-
- if (vma_iter_end(vmi) > end)
- next = vma_iter_load(vmi);
-
- if (!next)
- next = vma_next(vmi);
+ } for_each_vma_range(*vmi, next, end);
if (unlikely(uf)) {
/*
@@ -2465,12 +2456,18 @@ do_vmi_align_munmap(struct vma_iterator
BUG_ON(count != test_count);
}
#endif
- /* Point of no return */
- vma_iter_set(vmi, start);
+ while (vma_iter_addr(vmi) > start)
+ vma_iter_prev_range(vmi);
+
if (vma_iter_clear_gfp(vmi, start, end, GFP_KERNEL))
return -ENOMEM;
mm->map_count -= count;
+ prev = vma_iter_prev_range(vmi);
+ next = vma_next(vmi);
+ if (next)
+ vma_iter_prev_range(vmi);
+
/*
* Do not downgrade mmap_lock if we are next to VM_GROWSDOWN or
* VM_GROWSUP VMA. Such VMAs can change their size under
_
Patches currently in -mm which might be from Liam.Howlett@xxxxxxxxxx are
mm-mprotect-fix-do_mprotect_pkey-limit-check.patch
maple_tree-add-benchmarking-for-mas_for_each.patch
maple_tree-add-benchmarking-for-mas_prev.patch
mm-move-unmap_vmas-declaration-to-internal-header.patch
mm-change-do_vmi_align_munmap-side-tree-index.patch
mm-remove-prev-check-from-do_vmi_align_munmap.patch
maple_tree-introduce-__mas_set_range.patch
mm-remove-re-walk-from-mmap_region.patch
maple_tree-adjust-node-allocation-on-mas_rebalance.patch
maple_tree-re-introduce-entry-to-mas_preallocate-arguments.patch
mm-use-vma_iter_clear_gfp-in-nommu.patch
mm-set-up-vma-iterator-for-vma_iter_prealloc-calls.patch
maple_tree-move-mas_wr_end_piv-below-mas_wr_extend_null.patch
maple_tree-update-mas_preallocate-testing.patch
maple_tree-refine-mas_preallocate-node-calculations.patch
maple_tree-reduce-resets-during-store-setup.patch
mm-mmap-change-vma-iteration-order-in-do_vmi_align_munmap.patch
userfaultfd-fix-regression-in-userfaultfd_unmap_prep.patch
