Re: [PATCH 3/5] mm/vmalloc.c: optimize code in decay_va_pool_node() a little bit

Baoquan He
2025-04-17T02:51:53Z

On 04/16/25 at 03:50pm, Uladzislau Rezki wrote:
> On Tue, Apr 15, 2025 at 10:39:50AM +0800, Baoquan He wrote:
> > When purge lazily freed vmap areas, VA stored in vn->pool[] will also be
> > taken away into free vmap tree partially or completely accordingly, that
> > is done in decay_va_pool_node(). When doing that, for each pool of node,
> > the whole list is detached from the pool for handling. At this time,
> > that pool is empty. It's not necessary to update the pool size each time
> > when one VA is removed and addded into free vmap tree.
> >
> > Here change code to update the pool size when attaching the pool back.
> >
> > Signed-off-by: Baoquan He <bhe@redhat.com>
> > ---
> > mm/vmalloc.c | 23 +++++++++++------------
> > 1 file changed, 11 insertions(+), 12 deletions(-)
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 488d69b56765..bf735c890878 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -2150,7 +2150,7 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay)
> > LIST_HEAD(decay_list);
> > struct rb_root decay_root = RB_ROOT;
> > struct vmap_area *va, *nva;
> > - unsigned long n_decay;
> > + unsigned long n_decay, len;
> > int i;
> >
> > for (i = 0; i < MAX_VA_SIZE_PAGES; i++) {
> > @@ -2164,22 +2164,20 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay)
> > list_replace_init(&vn->pool[i].head, &tmp_list);
> > spin_unlock(&vn->pool_lock);
> >
> > - if (full_decay)
> > - WRITE_ONCE(vn->pool[i].len, 0);
> > + len = n_decay = vn->pool[i].len;
> > + WRITE_ONCE(vn->pool[i].len, 0);
> >
> > /* Decay a pool by ~25% out of left objects. */
> > - n_decay = vn->pool[i].len >> 2;
> > + if (!full_decay)
> > + n_decay >>= 2;
> > + len -= n_decay;
> >
> > list_for_each_entry_safe(va, nva, &tmp_list, list) {
> > + if (!n_decay)
> > + break;
> > list_del_init(&va->list);
> > merge_or_add_vmap_area(va, &decay_root, &decay_list);
> > -
> > - if (!full_decay) {
> > - WRITE_ONCE(vn->pool[i].len, vn->pool[i].len - 1);
> > -
> > - if (!--n_decay)
> > - break;
> > - }
> > + n_decay--;
> > }
> >
> > /*
> > @@ -2188,9 +2186,10 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay)
> > * can populate the pool therefore a simple list replace
> > * operation takes place here.
> > */
> > - if (!full_decay && !list_empty(&tmp_list)) {
> > + if (!list_empty(&tmp_list)) {
> > spin_lock(&vn->pool_lock);
> > list_replace_init(&tmp_list, &vn->pool[i].head);
> > + vn->pool[i].len = len;
> > spin_unlock(&vn->pool_lock);
> > }
> > }
> > --
> > 2.41.0
> >
> Which Linux version this patch is based on? I can not apply it.

I can apply them on the latest mainline kernel, next/master and
mm-new branch of akpm/mm.git. I checked just now.

>
> Small nits:
>
> <snip>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index c909b8fea6eb..0ae53c997219 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2150,7 +2150,7 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay)
> LIST_HEAD(decay_list);
> struct rb_root decay_root = RB_ROOT;
> struct vmap_area *va, *nva;
> - unsigned long n_decay, len;
> + unsigned long n_decay, pool_len;
> int i;
>
> for (i = 0; i < MAX_VA_SIZE_PAGES; i++) {
> @@ -2164,21 +2164,20 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay)
> list_replace_init(&vn->pool[i].head, &tmp_list);
> spin_unlock(&vn->pool_lock);
>
> - len = n_decay = vn->pool[i].len;
> + pool_len = n_decay = vn->pool[i].len;
> WRITE_ONCE(vn->pool[i].len, 0);
>
> /* Decay a pool by ~25% out of left objects. */
> if (!full_decay)
> n_decay >>= 2;
> - len -= n_decay;
> + pool_len -= n_decay;
>
> list_for_each_entry_safe(va, nva, &tmp_list, list) {
> - if (!n_decay)
> + if (!n_decay--)
> break;
>
> list_del_init(&va->list);
> merge_or_add_vmap_area(va, &decay_root, &decay_list);
> - n_decay--;
> }
>
> /*
> @@ -2190,7 +2189,7 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay)
> if (!list_empty(&tmp_list)) {
> spin_lock(&vn->pool_lock);
> list_replace_init(&tmp_list, &vn->pool[i].head);
> - vn->pool[i].len = len;
> + vn->pool[i].len = pool_len;
> spin_unlock(&vn->pool_lock);
> }
> }
> <snip>
>
> on top of this?
>
> a) decay in "if" statement, no need extra line;
> b) rename len to something obvious - pool_len.

All look good, will add them to this patch 3 of v2. Thanks a lot.