On 2021/6/25 13:01, Muchun Song wrote:
> On Thu, Jun 24, 2021 at 8:40 PM Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote:
>>
>> atomic_long_dec_and_test() is equivalent to atomic_long_dec() and
>> atomic_long_read() == 0. Use it to make code more succinct.
>
> Actually, they are not equal. atomic_long_dec_and_test implies a
> full memory barrier around it but atomic_long_dec and atomic_long_read
> don't.
>
Many thanks for comment. They are indeed not completely equal as you said.
What I mean is they can do the same things we want in this specified context.
Thanks again.
> That RMW operations that have a return value is equal to the following.
>
> smp_mb__before_atomic()
> non-RMW operations or RMW operations that have no return value
> smp_mb__after_atomic()
>
> Thanks.
>
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
>> ---
>> mm/zsmalloc.c | 3 +--
>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
>> index 1476289b619f..0b4b23740d78 100644
>> --- a/mm/zsmalloc.c
>> +++ b/mm/zsmalloc.c
>> @@ -1828,13 +1828,12 @@ static void putback_zspage_deferred(struct zs_pool *pool,
>> static inline void zs_pool_dec_isolated(struct zs_pool *pool)
>> {
>> VM_BUG_ON(atomic_long_read(&pool->isolated_pages) <= 0);
>> - atomic_long_dec(&pool->isolated_pages);
>> /*
>> * There's no possibility of racing, since wait_for_isolated_drain()
>> * checks the isolated count under &class->lock after enqueuing
>> * on migration_wait.
>> */
>> - if (atomic_long_read(&pool->isolated_pages) == 0 && pool->destroying)
>> + if (atomic_long_dec_and_test(&pool->isolated_pages) && pool->destroying)
>> wake_up_all(&pool->migration_wait);
>> }
>>
>> --
>> 2.23.0
>>
> .
>
