> vread() has been linearly searching vmap_area_list for looking up
> vmalloc areas to read from. These same areas are also tracked by
> a rb_tree (vmap_area_root) which offers logarithmic lookup.
>
> This patch modifies vread() to use the rb_tree structure instead
> of the list and the speedup for heavy /proc/kcore readers can
> be pretty significant. Below are the wall clock measurements of
> a Python application that leverages the drgn debugging library
> to read and interpret data read from /proc/kcore.
>
> Before the patch:
> -----
> $ time sudo sdb -e 'dbuf | head 3000 | wc'
> (unsigned long)3000
>
> real 0m22.446s
> user 0m2.321s
> sys 0m20.690s
> -----
>
> With the patch:
> -----
> $ time sudo sdb -e 'dbuf | head 3000 | wc'
> (unsigned long)3000
>
> real 0m2.104s
> user 0m2.043s
> sys 0m0.921s
> -----
>
> Signed-off-by: Serapheim Dimitropoulos <serapheim@xxxxxxxxxxx>
> ---
> Changed in v2:
>
> - Use __find_vmap_area() for initial lookup but keep iteration via
> va->list.
>
> mm/vmalloc.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 49ab9b6c001d..eb133d000394 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2860,7 +2860,10 @@ long vread(char *buf, char *addr, unsigned long count)
> count = -(unsigned long) addr;
>
> spin_lock(&vmap_area_lock);
> - list_for_each_entry(va, &vmap_area_list, list) {
> + va = __find_vmap_area((unsigned long)addr);
> + if (!va)
> + goto finished;
> + list_for_each_entry_from(va, &vmap_area_list, list) {
> if (!count)
> break;
>
> --
> 2.17.1
>
Much better :)
Reviewed-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
--
Vlad Rezki
