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SubjectRe: [PATCH v2] mm/vmalloc: terminate searching since one node found
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On 07/17/2017 04:07 PM, Zhaoyang Huang wrote:
> It is no need to find the very beginning of the area within
> alloc_vmap_area, which can be done by judging each node during the process
>
> For current approach, the worst case is that the starting node which be found
> for searching the 'vmap_area_list' is close to the 'vstart', while the final
> available one is round to the tail(especially for the left branch).
> This commit have the list searching start at the first available node, which
> will save the time of walking the rb tree'(1)' and walking the list(2).
>
> vmap_area_root
> / \
> tmp_next U
> / (1)
> tmp
> /
> ...
> /
> first(current approach)
>
> vmap_area_list->...->first->...->tmp->tmp_next

the original code can ensure the following two points :
A, the result vamp_area has the lowest available address in the range [vstart, vend)
B, it can maintain the cached vamp_area node rightly which can speedup relative allocation
i suspect this patch maybe destroy the above two points
> (2)
>
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@spreadtrum.com>
> ---
> mm/vmalloc.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 34a1c3e..f833e07 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -459,9 +459,16 @@ static struct vmap_area *alloc_vmap_area(unsigned
> long size,
>
> while (n) {
> struct vmap_area *tmp;
> + struct vmap_area *tmp_next;
> tmp = rb_entry(n, struct vmap_area, rb_node);
> + tmp_next = list_next_entry(tmp, list);
> if (tmp->va_end >= addr) {
> first = tmp;
> + if (ALIGN(tmp->va_end, align) + size
> + < tmp_next->va_start) {
> + addr = ALIGN(tmp->va_end, align);
> + goto found;
> + }
is the aim vamp_area the lowest available one if the goto occurs ?
it will bypass the latter cached vamp_area info cached_hole_size update possibly if the goto occurs
> if (tmp->va_start <= addr)
> break;
> n = n->rb_left;
> --
> 1.9.1
>


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