Re: [PATCH 1/2] io_uring: Move from hlist to io_wq_work_node

[Pavel Begunkov <asml.silence@gmail.com>]

On 2/21/23 18:38, Breno Leitao wrote:
> On 21/02/2023 17:45, Pavel Begunkov wrote:
>> On 2/21/23 13:57, Breno Leitao wrote:
>>> Having cache entries linked using the hlist format brings no benefit, and
>>> also requires an unnecessary extra pointer address per cache entry.
>>>
>>> Use the internal io_wq_work_node single-linked list for the internal
>>> alloc caches (async_msghdr and async_poll)
>>>
>>> This is required to be able to use KASAN on cache entries, since we do
>>> not need to touch unused (and poisoned) cache entries when adding more
>>> entries to the list.
>>
>> Looks good, a few nits
>>
>>>
>>> Suggested-by: Pavel Begunkov <asml.silence@gmail.com>
>>> Signed-off-by: Breno Leitao <leitao@debian.org>
>>> ---
>>>    include/linux/io_uring_types.h |  2 +-
>>>    io_uring/alloc_cache.h         | 27 +++++++++++++++------------
>>>    2 files changed, 16 insertions(+), 13 deletions(-)
>>>
>>> diff --git a/include/linux/io_uring_types.h
>>> b/include/linux/io_uring_types.h
>>> index 0efe4d784358..efa66b6c32c9 100644
>>> --- a/include/linux/io_uring_types.h
>>> +++ b/include/linux/io_uring_types.h
>>> @@ -188,7 +188,7 @@ struct io_ev_fd {
>>>    };
>>>    
>> [...]
>>> -    if (!hlist_empty(&cache->list)) {
>>> -        struct hlist_node *node = cache->list.first;
>>> -
>>> -        hlist_del(node);
>>> -        return container_of(node, struct io_cache_entry, node);
>>> +    struct io_wq_work_node *node;
>>> +    struct io_cache_entry *entry;
>>> +
>>> +    if (cache->list.next) {
>>> +        node = cache->list.next;
>>> +        entry = container_of(node, struct io_cache_entry, node);
>>
>> I'd prefer to get rid of the node var, it'd be a bit cleaner
>> than keeping two pointers to the same chunk.
>>
>> entry = container_of(node, struct io_cache_entry,
>>                       cache->list.next);
>>
>>> +        cache->list.next = node->next;
>>> +        return entry;
>>>        }
>>>          return NULL;
>>> @@ -35,19 +38,19 @@ static inline struct io_cache_entry
>>> *io_alloc_cache_get(struct io_alloc_cache *c
>>>      static inline void io_alloc_cache_init(struct io_alloc_cache *cache)
>>>    {
>>> -    INIT_HLIST_HEAD(&cache->list);
>>> +    cache->list.next = NULL;
>>>        cache->nr_cached = 0;
>>>    }
>>>      static inline void io_alloc_cache_free(struct io_alloc_cache *cache,
>>>                        void (*free)(struct io_cache_entry *))
>>>    {
>>> -    while (!hlist_empty(&cache->list)) {
>>> -        struct hlist_node *node = cache->list.first;
>>> +    struct io_cache_entry *entry;
>>>    -        hlist_del(node);
>>> -        free(container_of(node, struct io_cache_entry, node));
>>> +    while ((entry = io_alloc_cache_get(cache))) {
>>> +        free(entry);
>>
>> We don't need brackets here.
> 
> The extra brackets are required if we are assignments in if, otherwise
> the compiler raises a warning (bugprone-assignment-in-if-condition)

I mean braces / curly brackets.
>> Personally, I don't have anything
>> against assignments in if, but it's probably better to avoid them
> 
> Sure. I will remove the assignents in "if" part and maybe replicate what
> we have
> in io_alloc_cache_get(). Something as:
>         if (cache->list.next) {
>                 node = cache->list.next;
> 
> Thanks for the review!

-- 
Pavel Begunkov