On 2024/1/23 10:51, Chengming Zhou wrote:
> On 2024/1/23 01:13, Vlastimil Babka wrote:
>> On 1/19/24 04:53, Chengming Zhou wrote:
>>> On 2024/1/19 06:14, Christoph Lameter (Ampere) wrote:
>>>> On Thu, 18 Jan 2024, Chengming Zhou wrote:
>>>>
>>>>> So get_freelist() has two cases to handle: cpu slab and cpu partial list slab.
>>>>> The latter is NOT frozen, so need to remove "VM_BUG_ON(!new.frozen)" from it.
>>>>
>>>> Right so keep the check if it is the former?
>>>>
>>>
>>> Ok, I get it. Maybe like this:
>>
>> I think that's just too ugly for a VM_BUG_ON(). I'd just remove the check
>> and be done with that.
>
> Ok with me.
>
>>
>> I have a somewhat different point. You reused get_freelist() but in fact
>> it's more like freeze_slab(), but that one uses slab_update_freelist() and
>> we are under the local_lock so we want the cheaper __slab_update_freelist(),
>> which get_freelist() has and I guess that's why you reused that one.
>
> Right, we already have the lock_lock, so reuse get_freelist().
>
>>
>> However get_freelist() also assumes it can return NULL if the freelist is
>> empty. If that's possible to happen on the percpu partial list, we should
>> not "goto load_freelist;" but rather create a new label above that, above
>> the "if (!freelist) {" block that handles the case.
>>
>> If that's not possible to happen (needs careful audit) and we have guarantee
>
> Yes, it's not possible for now.
>
>> that slabs on percpu partial list must have non-empty freelist, then we
>> probably instead want a new __freeze_slab() variant that is like
>> freeze_slab(), but uses __slab_update_freelist() and probably also has
>> VM_BUG_ON(!freelist) before returning it?
>>
>
> Instead of introducing another new function, how about still reusing get_freelist()
> and VM_BUG_ON(!freelist) after calling it? I feel this is simpler.
>
> Thanks!
Does this look fine?
diff --git a/mm/slub.c b/mm/slub.c
index 2ef88bbf56a3..fda402b2d649 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3326,7 +3326,6 @@ static inline void *get_freelist(struct kmem_cache *s, struct slab *slab)
counters = slab->counters;
new.counters = counters;
- VM_BUG_ON(!new.frozen);
new.inuse = slab->objects;
new.frozen = freelist != NULL;
@@ -3498,18 +3497,20 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
slab = slub_percpu_partial(c);
slub_set_percpu_partial(c, slab);
- local_unlock_irqrestore(&s->cpu_slab->lock, flags);
- stat(s, CPU_PARTIAL_ALLOC);
- if (unlikely(!node_match(slab, node) ||
- !pfmemalloc_match(slab, gfpflags))) {
- slab->next = NULL;
- __put_partials(s, slab);
- continue;
+ if (likely(node_match(slab, node) &&
+ pfmemalloc_match(slab, gfpflags))) {
+ c->slab = slab;
+ freelist = get_freelist(s, slab);
+ VM_BUG_ON(!freelist);
+ stat(s, CPU_PARTIAL_ALLOC);
+ goto load_freelist;
}
- freelist = freeze_slab(s, slab);
- goto retry_load_slab;
+ local_unlock_irqrestore(&s->cpu_slab->lock, flags);
+
+ slab->next = NULL;
+ __put_partials(s, slab);
}
#endif
