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SubjectRe: [PATCH 1/2] io_uring: Move from hlist to io_wq_work_node
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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. Personally, I don't have anything
against assignments in if, but it's probably better to avoid them,
or there will be a patch in a couple of months based on a random
code analysis report as happened many times before.

while (1) {
struct io_cache_entry *entry = get();

if (!entry)
break;
free(entry);
}

--
Pavel Begunkov

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