On Tue, Dec 20, 2022 at 07:27:03PM +0100, Uladzislau Rezki (Sony) wrote:
> When a VA is freed over a main path, for example by invoking
> the vfree() function, a tree is accessed two times what is odd:
>
> vfree():
> __vunmap()
> __find_vmap_area()
> vm_remove_mappings()
> remove_vm_area()
> __find_vmap_area()
>
> __find_vmap_area() are called two times. Fix it by introducing
> a find_unlink_vmap_area() helper that finds and un-links a VA
> from a tree.
>
> Performance test results on a single CPU:
>
> - fix_size_alloc_test loops: 1000000 avg: 476847 usec
> - full_fit_alloc_test loops: 1000000 avg: 806746 usec
> - long_busy_list_alloc_test loops: 1000000 avg: 13552093 usec
> - random_size_alloc_test loops: 1000000 avg: 7441322 usec
> - fix_align_alloc_test loops: 1000000 avg: 1411132 usec
> All test took worker0=87650866284 cycles
>
> - fix_size_alloc_test loops: 1000000 avg: 490713 usec
> - full_fit_alloc_test loops: 1000000 avg: 579162 usec
> - long_busy_list_alloc_test loops: 1000000 avg: 10485448 usec
> - random_size_alloc_test loops: 1000000 avg: 5824449 usec
> - fix_align_alloc_test loops: 1000000 avg: 984735 usec
> All test took worker0=67952362802 cycles
>
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
> ---
> mm/vmalloc.c | 40 ++++++++++++++++++++++++++++------------
> 1 file changed, 28 insertions(+), 12 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 9e30f0b39203..0fc38c36e0df 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1825,9 +1825,14 @@ static void free_vmap_area_noflush(struct vmap_area *va)
> unsigned long va_start = va->va_start;
> unsigned long nr_lazy;
>
> - spin_lock(&vmap_area_lock);
> - unlink_va(va, &vmap_area_root);
> - spin_unlock(&vmap_area_lock);
> + /*
> + * A free_vmap_block() is left. It is NOT a main free path.
> + */
> + if (!list_empty(&va->list)) {
> + spin_lock(&vmap_area_lock);
> + unlink_va(va, &vmap_area_root);
> + spin_unlock(&vmap_area_lock);
> + }
>
> nr_lazy = atomic_long_add_return((va->va_end - va->va_start) >>
> PAGE_SHIFT, &vmap_lazy_nr);
> @@ -1871,6 +1876,19 @@ struct vmap_area *find_vmap_area(unsigned long addr)
> return va;
> }
>
> +static struct vmap_area *find_unlink_vmap_area(unsigned long addr)
> +{
> + struct vmap_area *va;
> +
> + spin_lock(&vmap_area_lock);
> + va = __find_vmap_area(addr, &vmap_area_root);
> + if (va)
> + unlink_va(va, &vmap_area_root);
> + spin_unlock(&vmap_area_lock);
> +
> + return va;
> +}
> +
> /*** Per cpu kva allocator ***/
>
> /*
> @@ -2236,7 +2254,7 @@ void vm_unmap_ram(const void *mem, unsigned int count)
> return;
> }
>
> - va = find_vmap_area(addr);
> + va = find_unlink_vmap_area(addr);
> BUG_ON(!va);
> debug_check_no_locks_freed((void *)va->va_start,
> (va->va_end - va->va_start));
> @@ -2607,21 +2625,16 @@ struct vm_struct *remove_vm_area(const void *addr)
>
> might_sleep();
>
> - spin_lock(&vmap_area_lock);
> - va = __find_vmap_area((unsigned long)addr, &vmap_area_root);
> - if (va && va->vm) {
> + va = find_unlink_vmap_area((unsigned long) addr);
> + if (va) {
> struct vm_struct *vm = va->vm;
>
> - va->vm = NULL;
> - spin_unlock(&vmap_area_lock);
> -
> kasan_free_module_shadow(vm);
> free_unmap_vmap_area(va);
>
> return vm;
> }
>
> - spin_unlock(&vmap_area_lock);
> return NULL;
> }
>
> @@ -2690,6 +2703,7 @@ static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages)
> static void __vunmap(const void *addr, int deallocate_pages)
> {
> struct vm_struct *area;
> + struct vmap_area *va;
>
> if (!addr)
> return;
> @@ -2698,7 +2712,9 @@ static void __vunmap(const void *addr, int deallocate_pages)
> addr))
> return;
>
> - area = find_vm_area(addr);
> + va = find_unlink_vmap_area((unsigned long)addr);
> + area = va->vm;
> +
> if (unlikely(!area)) {
> WARN(1, KERN_ERR "Trying to vfree() nonexistent vm area (%p)\n",
> addr);
> --
> 2.30.2
>
Will send a v2.
--
Uladzislau Rezki
