From:   Gabriel Krisman Bertazi <krisman@suse.de>
To:     Breno Leitao <leitao@debian.org>
Cc:     axboe@kernel.dk, asml.silence@gmail.com, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org, gustavold@meta.com, leit@meta.com,
        kasan-dev@googlegroups.com
Subject: Re: [PATCH v3 1/2] io_uring: Move from hlist to io_wq_work_node
References: <20230223164353.2839177-1-leitao@debian.org>
        <20230223164353.2839177-2-leitao@debian.org>
Date:   Thu, 23 Feb 2023 16:02:25 -0300
In-Reply-To: <20230223164353.2839177-2-leitao@debian.org> (Breno Leitao's
        message of "Thu, 23 Feb 2023 08:43:52 -0800")
Message-ID: <87wn48ryri.fsf@suse.de>
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Breno Leitao <leitao@debian.org> writes:

> 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.
>

Looking at this patch, I wonder if it could go in the opposite direction
instead, and drop io_wq_work_node entirely in favor of list_head. :)

Do we gain anything other than avoiding the backpointer with a custom
linked implementation, instead of using the interface available in
list.h, that developers know how to use and has other features like
poisoning and extra debug checks?


>  static inline struct io_cache_entry *io_alloc_cache_get(struct io_alloc_cache *cache)
>  {
> -	if (!hlist_empty(&cache->list)) {
> -		struct hlist_node *node = cache->list.first;
> +	if (cache->list.next) {
> +		struct io_cache_entry *entry;
>  
> -		hlist_del(node);
> -		return container_of(node, struct io_cache_entry, node);
> +		entry = container_of(cache->list.next, struct io_cache_entry, node);
> +		cache->list.next = cache->list.next->next;
> +		return entry;
>  	}

From a quick look, I think you could use wq_stack_extract() here

-- 
Gabriel Krisman Bertazi