The patch titled
Subject: mm: vmalloc: clean up vunmap to avoid pgtable ops twice
has been added to the -mm tree. Its filename is
mm-vmalloc-clean-up-vunmap-to-avoid-pgtable-ops-twice.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-vmalloc-clean-up-vunmap-to-avoid-pgtable-ops-twice.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-vmalloc-clean-up-vunmap-to-avoid-pgtable-ops-twice.patch
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------------------------------------------------------
From: Chintan Pandya <cpandya@xxxxxxxxxxxxxx>
Subject: mm: vmalloc: clean up vunmap to avoid pgtable ops twice
vunmap does page table clear operations twice in the case when
DEBUG_PAGEALLOC_ENABLE_DEFAULT is enabled.
So, clean up the code as that is unintended.
As a perf gain, we save few us. Below ftrace data was obtained while
doing 1 MB of vmalloc/vfree on ARM64 based SoC *without* this patch
applied. After this patch, we can save ~3 us (on 1 extra
vunmap_page_range).
CPU DURATION FUNCTION CALLS
| | | | | | |
6) | __vunmap() {
6) | vmap_debug_free_range() {
6) 3.281 us | vunmap_page_range();
6) + 45.468 us | }
6) 2.760 us | vunmap_page_range();
6) ! 505.105 us | }
Link: http://lkml.kernel.org/r/1523876342-10545-1-git-send-email-cpandya@xxxxxxxxxxxxxx
Signed-off-by: Chintan Pandya <cpandya@xxxxxxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Laura Abbott <labbott@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Florian Fainelli <f.fainelli@xxxxxxxxx>
Cc: Yisheng Xie <xieyisheng1@xxxxxxxxxx>
Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Cc: Wei Yang <richard.weiyang@xxxxxxxxx>
Cc: Byungchul Park <byungchul.park@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmalloc.c | 25 +++----------------------
1 file changed, 3 insertions(+), 22 deletions(-)
diff -puN mm/vmalloc.c~mm-vmalloc-clean-up-vunmap-to-avoid-pgtable-ops-twice mm/vmalloc.c
--- a/mm/vmalloc.c~mm-vmalloc-clean-up-vunmap-to-avoid-pgtable-ops-twice
+++ a/mm/vmalloc.c
@@ -603,26 +603,6 @@ static void unmap_vmap_area(struct vmap_
vunmap_page_range(va->va_start, va->va_end);
}
-static void vmap_debug_free_range(unsigned long start, unsigned long end)
-{
- /*
- * Unmap page tables and force a TLB flush immediately if pagealloc
- * debugging is enabled. This catches use after free bugs similarly to
- * those in linear kernel virtual address space after a page has been
- * freed.
- *
- * All the lazy freeing logic is still retained, in order to minimise
- * intrusiveness of this debugging feature.
- *
- * This is going to be *slow* (linear kernel virtual address debugging
- * doesn't do a broadcast TLB flush so it is a lot faster).
- */
- if (debug_pagealloc_enabled()) {
- vunmap_page_range(start, end);
- flush_tlb_kernel_range(start, end);
- }
-}
-
/*
* lazy_max_pages is the maximum amount of virtual address space we gather up
* before attempting to purge with a TLB flush.
@@ -756,6 +736,9 @@ static void free_unmap_vmap_area(struct
{
flush_cache_vunmap(va->va_start, va->va_end);
unmap_vmap_area(va);
+ if (debug_pagealloc_enabled())
+ flush_tlb_kernel_range(va->va_start, va->va_end);
+
free_vmap_area_noflush(va);
}
@@ -1142,7 +1125,6 @@ void vm_unmap_ram(const void *mem, unsig
BUG_ON(!PAGE_ALIGNED(addr));
debug_check_no_locks_freed(mem, size);
- vmap_debug_free_range(addr, addr+size);
if (likely(count <= VMAP_MAX_ALLOC)) {
vb_free(mem, size);
@@ -1499,7 +1481,6 @@ struct vm_struct *remove_vm_area(const v
va->flags |= VM_LAZY_FREE;
spin_unlock(&vmap_area_lock);
- vmap_debug_free_range(va->va_start, va->va_end);
kasan_free_shadow(vm);
free_unmap_vmap_area(va);
_
Patches currently in -mm which might be from cpandya@xxxxxxxxxxxxxx are
mm-vmalloc-clean-up-vunmap-to-avoid-pgtable-ops-twice.patch
mm-vmalloc-avoid-racy-handling-of-debugobjects-in-vunmap.patch
mm-vmalloc-pass-proper-vm_start-into-debugobjects.patch
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