Messages in this thread | | | From | Muchun Song <> | Date | Fri, 25 Jun 2021 13:01:53 +0800 | Subject | Re: [Phishing Risk] [External] [PATCH 2/3] mm/zsmalloc.c: combine two atomic ops in zs_pool_dec_isolated() |
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On Thu, Jun 24, 2021 at 8:40 PM Miaohe Lin <linmiaohe@huawei.com> 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.
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@huawei.com> > --- > 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 >
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