Re: amusing SLUB compaction bug when CC_OPTIMIZE_FOR_SIZE

Vlastimil Babka
2022-09-29T13:01:22Z

On 9/29/22 13:53, David Laight wrote:
>> -static void rcu_free_slab(struct rcu_head *h)
>> +/*
>> + * rcu_free_slab() must be __aligned(4) because its address is saved
>> + * in the rcu_head field, which coincides with page->mapping, which
>> + * causes trouble if compaction mistakes it for PAGE_MAPPING_MOVABLE.
>> + */
>> +__aligned(4) static void rcu_free_slab(struct rcu_head *h)
>> {
>> struct slab *slab = container_of(h, struct slab, rcu_head);
>>
>
> Isn't that going to cause grief with options that align
> functions on 16/32byte boundaries when adding space for
> 'other stuff'?

How is that done exactly? Also having higher alignment (16/32) is not in
conflict with asking for 4?

> David
>
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