On 8/11/21 1:19 PM, Muchun Song wrote:
> The commit d6e0b7fa1186 ("slub: make dead caches discard free slabs
> immediately") introduced those logic to speed up the destruction of
> per-memcg kmem caches, because kmem caches created for a memory
> cgroup are only destroyed after the last page charged to the cgroup
> is freed at that time. But since commit 9855609bde03 ("mm: memcg/slab:
> use a single set of kmem_caches for all accounted allocations), we
> do not have per-memcg kmem caches anymore. Are those code pointless?
> No, the kmem_cache->cpu_partial can be set to zero by 'echo 0 > /sys/
> kernel/slab/*/cpu_partial'. In this case, the slab page will be put
> into cpu partial list and then moved to node list (because
> slub_cpu_partial() returns zero). However, we can skip putting the
> slab page to cpu partial list and just move it to node list directly.
> We can adjust the condition of kmem_cache_has_cpu_partial() to
> slub_cpu_partial() in __slab_free() and remove those code from
> put_cpu_partial() for simplification.
>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Please check again current mmotm/next if this still applies, I think it
shouldn't anymore. Thanks.
> ---
> mm/slub.c | 23 +++--------------------
> 1 file changed, 3 insertions(+), 20 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index b6c5205252eb..69c8ada322a0 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2438,7 +2438,6 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)
> int pages;
> int pobjects;
>
> - preempt_disable();
> do {
> pages = 0;
> pobjects = 0;
> @@ -2470,16 +2469,7 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)
> page->pobjects = pobjects;
> page->next = oldpage;
>
> - } while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page)
> - != oldpage);
> - if (unlikely(!slub_cpu_partial(s))) {
> - unsigned long flags;
> -
> - local_irq_save(flags);
> - unfreeze_partials(s, this_cpu_ptr(s->cpu_slab));
> - local_irq_restore(flags);
> - }
> - preempt_enable();
> + } while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page) != oldpage);
> #endif /* CONFIG_SLUB_CPU_PARTIAL */
> }
>
> @@ -3059,9 +3049,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
> was_frozen = new.frozen;
> new.inuse -= cnt;
> if ((!new.inuse || !prior) && !was_frozen) {
> -
> - if (kmem_cache_has_cpu_partial(s) && !prior) {
> -
> + if (slub_cpu_partial(s) && !prior) {
> /*
> * Slab was on no list before and will be
> * partially empty
> @@ -3069,9 +3057,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
> * freeze it.
> */
> new.frozen = 1;
> -
> } else { /* Needs to be taken off a list */
> -
> n = get_node(s, page_to_nid(page));
> /*
> * Speculatively acquire the list_lock.
> @@ -3082,17 +3068,14 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
> * other processors updating the list of slabs.
> */
> spin_lock_irqsave(&n->list_lock, flags);
> -
> }
> }
> -
> } while (!cmpxchg_double_slab(s, page,
> prior, counters,
> head, new.counters,
> "__slab_free"));
>
> if (likely(!n)) {
> -
> if (likely(was_frozen)) {
> /*
> * The list lock was not taken therefore no list
> @@ -3118,7 +3101,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
> * Objects left in the slab. If it was not on the partial list before
> * then add it.
> */
> - if (!kmem_cache_has_cpu_partial(s) && unlikely(!prior)) {
> + if (unlikely(!prior)) {
> remove_full(s, n, page);
> add_partial(n, page, DEACTIVATE_TO_TAIL);
> stat(s, FREE_ADD_PARTIAL);
>
