On 2023/10/31 19:15, Vlastimil Babka wrote:
> On 10/24/23 11:33, chengming.zhou@xxxxxxxxx wrote:
>> From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
>>
>> Since the introduce of unfrozen slabs on cpu partial list, we don't
>> need to synchronize the slab frozen state under the node list_lock.
>>
>> The caller of deactivate_slab() and the caller of __slab_free() won't
>> manipulate the slab list concurrently.
>>
>> So we can get node list_lock in the last stage if we really need to
>> manipulate the slab list in this path.
>>
>> Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
>
> Nice simplification!
>
>> ---
>> mm/slub.c | 70 ++++++++++++++++++++-----------------------------------
>> 1 file changed, 25 insertions(+), 45 deletions(-)
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 486d44421432..64d550e415eb 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -2449,10 +2449,8 @@ static void init_kmem_cache_cpus(struct kmem_cache *s)
>> static void deactivate_slab(struct kmem_cache *s, struct slab *slab,
>> void *freelist)
>> {
>> - enum slab_modes { M_NONE, M_PARTIAL, M_FREE, M_FULL_NOLIST };
>> struct kmem_cache_node *n = get_node(s, slab_nid(slab));
>> int free_delta = 0;
>> - enum slab_modes mode = M_NONE;
>> void *nextfree, *freelist_iter, *freelist_tail;
>> int tail = DEACTIVATE_TO_HEAD;
>> unsigned long flags = 0;
>> @@ -2499,58 +2497,40 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab,
>> * unfrozen and number of objects in the slab may have changed.
>> * Then release lock and retry cmpxchg again.
>> */
>
> This comment above (including parts not visible here) should be updated as
> there is no more list manipulation during unfreeze.
Right!
>
>> -redo:
>> -
>> - old.freelist = READ_ONCE(slab->freelist);
>> - old.counters = READ_ONCE(slab->counters);
>> - VM_BUG_ON(!old.frozen);
>> -
>> - /* Determine target state of the slab */
>> - new.counters = old.counters;
>> - if (freelist_tail) {
>> - new.inuse -= free_delta;
>> - set_freepointer(s, freelist_tail, old.freelist);
>> - new.freelist = freelist;
>> - } else
>> - new.freelist = old.freelist;
>> + do {
>> + old.freelist = READ_ONCE(slab->freelist);
>> + old.counters = READ_ONCE(slab->counters);
>> + VM_BUG_ON(!old.frozen);
>> +
>> + /* Determine target state of the slab */
>> + new.counters = old.counters;
>> + new.frozen = 0;
>> + if (freelist_tail) {
>> + new.inuse -= free_delta;
>> + set_freepointer(s, freelist_tail, old.freelist);
>> + new.freelist = freelist;
>> + } else
>> + new.freelist = old.freelist;
>
> Per coding style we should have the else with { } even if it's one line, to
> match the if branch. Since we touch the code that was previously violating
> the style, we can fix up.
Ok, I will fix all these.
Big thanks for your review!
>
>>
>> - new.frozen = 0;
>> + } while (!slab_update_freelist(s, slab,
>> + old.freelist, old.counters,
>> + new.freelist, new.counters,
>> + "unfreezing slab"));
>>
>> + /*
>> + * Stage three: Manipulate the slab list based on the updated state.
>> + */
>> if (!new.inuse && n->nr_partial >= s->min_partial) {
>> - mode = M_FREE;
>> + stat(s, DEACTIVATE_EMPTY);
>> + discard_slab(s, slab);
>> + stat(s, FREE_SLAB);
>> } else if (new.freelist) {
>> - mode = M_PARTIAL;
>> - /*
>> - * Taking the spinlock removes the possibility that
>> - * acquire_slab() will see a slab that is frozen
>> - */
>> spin_lock_irqsave(&n->list_lock, flags);
>> - } else {
>> - mode = M_FULL_NOLIST;
>> - }
>> -
>> -
>> - if (!slab_update_freelist(s, slab,
>> - old.freelist, old.counters,
>> - new.freelist, new.counters,
>> - "unfreezing slab")) {
>> - if (mode == M_PARTIAL)
>> - spin_unlock_irqrestore(&n->list_lock, flags);
>> - goto redo;
>> - }
>> -
>> -
>> - if (mode == M_PARTIAL) {
>> add_partial(n, slab, tail);
>> spin_unlock_irqrestore(&n->list_lock, flags);
>> stat(s, tail);
>> - } else if (mode == M_FREE) {
>> - stat(s, DEACTIVATE_EMPTY);
>> - discard_slab(s, slab);
>> - stat(s, FREE_SLAB);
>> - } else if (mode == M_FULL_NOLIST) {
>> + } else
>> stat(s, DEACTIVATE_FULL);
>> - }
>
> Same here.
>
> Thanks!
>
>> }
>>
>> #ifdef CONFIG_SLUB_CPU_PARTIAL
>
