UbiquitousOS
/
OpenCloudOS-Kernel
mirror of https://gitee.com/OpenCloudOS/OpenCloudOS-Kernel.git
11
0
Fork 0
Code Issues Projects Releases Wiki Activity

mm/mmap: change vma iteration order in do_vmi_align_munmap() 

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 requires changing the loop type when gathering the VMAs that will
be freed.

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/20230724183157.3939892-16-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Liam R. Howlett 2023-07-24 14:31:57 -04:00 committed by Andrew Morton
parent fec2936434
commit 6935e05255
1 changed files with 13 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
mm/mmap.c
View File

@ -2452,20 +2452,17 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
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);
@ -2501,13 +2498,7 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
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 defined(CONFIG_DEBUG_VM_MAPLE_TREE)
/* Make sure no VMAs are about to be lost. */
@ -2528,7 +2519,10 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
BUG_ON(count != test_count);
}
#endif
vma_iter_set(vmi, start);
while (vma_iter_addr(vmi) > start)
vma_iter_prev_range(vmi);
error = vma_iter_clear_gfp(vmi, start, end, GFP_KERNEL);
if (error)
goto clear_tree_failed;
@ -2539,6 +2533,11 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
if (unlock)
mmap_write_downgrade(mm);
prev = vma_iter_prev_range(vmi);
next = vma_next(vmi);
if (next)
vma_iter_prev_range(vmi);
/*
* We can free page tables without write-locking mmap_lock because VMAs
* were isolated before we downgraded mmap_lock.