On Mon, 31 May 2010 18:07:57 +1000
Nick Piggin <npiggin@xxxxxxx> wrote:
> Hi Andrew,
>
> Could you put this in your tree? It could do with a bit more testing. I
> will update you with updates or results from Steven.
>
> Thanks,
> Nick
> --
>
> Provide a free area cache for the vmalloc virtual address allocator, based
> on the approach taken in the user virtual memory allocator.
>
> This reduces the number of rbtree operations and linear traversals over
> the vmap extents to find a free area. The lazy vmap flushing makes this problem
> worse because because freed but not yet flushed vmaps tend to build up in
> the address space between flushes.
>
> Steven noticed a performance problem with GFS2. Results are as follows...
>
>
>
changelog got truncated - the "results" and the signoff are missing.
> --- linux-2.6.orig/mm/vmalloc.c
> +++ linux-2.6/mm/vmalloc.c
> @@ -262,8 +262,14 @@ struct vmap_area {
> };
>
> static DEFINE_SPINLOCK(vmap_area_lock);
> -static struct rb_root vmap_area_root = RB_ROOT;
> static LIST_HEAD(vmap_area_list);
> +static struct rb_root vmap_area_root = RB_ROOT;
> +
> +static struct rb_node *free_vmap_cache;
> +static unsigned long cached_hole_size;
> +static unsigned long cached_start;
> +static unsigned long cached_align;
> +
> static unsigned long vmap_area_pcpu_hole;
>
> static struct vmap_area *__find_vmap_area(unsigned long addr)
> @@ -332,9 +338,11 @@ static struct vmap_area *alloc_vmap_area
> struct rb_node *n;
> unsigned long addr;
> int purged = 0;
> + struct vmap_area *first;
>
> BUG_ON(!size);
> BUG_ON(size & ~PAGE_MASK);
> + BUG_ON(!is_power_of_2(align));
Worried. How do we know this won't trigger?
> va = kmalloc_node(sizeof(struct vmap_area),
> gfp_mask & GFP_RECLAIM_MASK, node);
> @@ -342,17 +350,39 @@ static struct vmap_area *alloc_vmap_area
> return ERR_PTR(-ENOMEM);
>
> retry:
> - addr = ALIGN(vstart, align);
> -
> spin_lock(&vmap_area_lock);
> - if (addr + size - 1 < addr)
> - goto overflow;
> + /* invalidate cache if we have more permissive parameters */
> + if (!free_vmap_cache ||
> + size <= cached_hole_size ||
> + vstart < cached_start ||
> + align < cached_align) {
> +nocache:
> + cached_hole_size = 0;
> + free_vmap_cache = NULL;
> + }
> + /* record if we encounter less permissive parameters */
> + cached_start = vstart;
> + cached_align = align;
> +
> + /* find starting point for our search */
> + if (free_vmap_cache) {
> + first = rb_entry(free_vmap_cache, struct vmap_area, rb_node);
> + addr = ALIGN(first->va_end + PAGE_SIZE, align);
> + if (addr < vstart)
> + goto nocache;
> + if (addr + size - 1 < addr)
> + goto overflow;
Some comments attached to the `if' tests would make it easier to
understand what's going on.
> +
> + } else {
> + addr = ALIGN(vstart, align);
> + if (addr + size - 1 < addr)
> + goto overflow;
> - /* XXX: could have a last_hole cache */
> - n = vmap_area_root.rb_node;
> - if (n) {
> - struct vmap_area *first = NULL;
> + n = vmap_area_root.rb_node;
> + if (!n)
> + goto found;
>
> + first = NULL;
> do {
> struct vmap_area *tmp;
> tmp = rb_entry(n, struct vmap_area, rb_node);
this?
--- a/mm/vmalloc.c~mm-vmap-area-cache-fix
+++ a/mm/vmalloc.c
@@ -265,6 +265,7 @@ static DEFINE_SPINLOCK(vmap_area_lock);
static LIST_HEAD(vmap_area_list);
static struct rb_root vmap_area_root = RB_ROOT;
+/* The vmap cache globals are protected by vmap_area_lock */
static struct rb_node *free_vmap_cache;
static unsigned long cached_hole_size;
static unsigned long cached_start;
_
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