* [PATCH] mm/vmalloc: use rb_tree instead of list for vread() lookups
@ 2021-02-08 15:53 Serapheim Dimitropoulos
2021-02-08 19:01 ` Uladzislau Rezki
0 siblings, 1 reply; 2+ messages in thread
From: Serapheim Dimitropoulos @ 2021-02-08 15:53 UTC (permalink / raw)
To: akpm, linux-mm; +Cc: linux-kernel, osandov, serapheim
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 2500 | wc'
(unsigned long)2500
real 0m21.128s
user 0m2.321s
sys 0m19.227s
-----
With the patch:
-----
$ time sudo sdb -e 'dbuf | head 2500 | wc'
(unsigned long)2500
real 0m1.870s
user 0m1.628s
sys 0m0.660s
-----
Signed-off-by: Serapheim Dimitropoulos <serapheim@delphix.com>
---
mm/vmalloc.c | 19 ++++++++++++-------
1 file changed, 12 insertions(+), 7 deletions(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 49ab9b6c001d..86343b879938 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2851,6 +2851,7 @@ long vread(char *buf, char *addr, unsigned long count)
{
struct vmap_area *va;
struct vm_struct *vm;
+ struct rb_node *node;
char *vaddr, *buf_start = buf;
unsigned long buflen = count;
unsigned long n;
@@ -2860,17 +2861,15 @@ 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) {
- if (!count)
- break;
-
+ va = __find_vmap_area((unsigned long)addr);
+ if (!va)
+ goto finished;
+ while (count) {
if (!va->vm)
- continue;
+ goto next_node;
vm = va->vm;
vaddr = (char *) vm->addr;
- if (addr >= vaddr + get_vm_area_size(vm))
- continue;
while (addr < vaddr) {
if (count == 0)
goto finished;
@@ -2889,6 +2888,12 @@ long vread(char *buf, char *addr, unsigned long count)
buf += n;
addr += n;
count -= n;
+
+next_node:
+ node = rb_next(&va->rb_node);
+ if (!node)
+ break;
+ va = rb_entry(node, struct vmap_area, rb_node);
}
finished:
spin_unlock(&vmap_area_lock);
--
2.17.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] mm/vmalloc: use rb_tree instead of list for vread() lookups
2021-02-08 15:53 [PATCH] mm/vmalloc: use rb_tree instead of list for vread() lookups Serapheim Dimitropoulos
@ 2021-02-08 19:01 ` Uladzislau Rezki
0 siblings, 0 replies; 2+ messages in thread
From: Uladzislau Rezki @ 2021-02-08 19:01 UTC (permalink / raw)
To: Serapheim Dimitropoulos; +Cc: akpm, linux-mm, linux-kernel, osandov, serapheim
On Mon, Feb 08, 2021 at 03:53:03PM +0000, Serapheim Dimitropoulos wrote:
> 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 2500 | wc'
> (unsigned long)2500
>
> real 0m21.128s
> user 0m2.321s
> sys 0m19.227s
> -----
>
> With the patch:
> -----
> $ time sudo sdb -e 'dbuf | head 2500 | wc'
> (unsigned long)2500
>
> real 0m1.870s
> user 0m1.628s
> sys 0m0.660s
> -----
>
> Signed-off-by: Serapheim Dimitropoulos <serapheim@delphix.com>
> ---
> mm/vmalloc.c | 19 ++++++++++++-------
> 1 file changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 49ab9b6c001d..86343b879938 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2851,6 +2851,7 @@ long vread(char *buf, char *addr, unsigned long count)
> {
> struct vmap_area *va;
> struct vm_struct *vm;
> + struct rb_node *node;
> char *vaddr, *buf_start = buf;
> unsigned long buflen = count;
> unsigned long n;
> @@ -2860,17 +2861,15 @@ 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) {
> - if (!count)
> - break;
> -
> + va = __find_vmap_area((unsigned long)addr);
> + if (!va)
> + goto finished;
> + while (count) {
> if (!va->vm)
> - continue;
> + goto next_node;
>
> vm = va->vm;
> vaddr = (char *) vm->addr;
> - if (addr >= vaddr + get_vm_area_size(vm))
> - continue;
> while (addr < vaddr) {
> if (count == 0)
> goto finished;
> @@ -2889,6 +2888,12 @@ long vread(char *buf, char *addr, unsigned long count)
> buf += n;
> addr += n;
> count -= n;
> +
> +next_node:
> + node = rb_next(&va->rb_node);
> + if (!node)
> + break;
> + va = rb_entry(node, struct vmap_area, rb_node);
>
You can also improve it. Instead of rb_next() you can directly access
to a "next" element via "va->list" making it O(1) complexity.
--
Vlad Rezki
^ permalink raw reply [flat|nested] 2+ messages in thread
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