linux-kernel - Re: [PATCH v3 1/2] io_uring: Move from hlist to io_wq_work

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Date:   Thu, 23 Feb 2023 12:39:25 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Gabriel Krisman Bertazi <krisman@...e.de>,
        Breno Leitao <leitao@...ian.org>
Cc:     asml.silence@...il.com, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org, gustavold@...a.com, leit@...a.com,
        kasan-dev@...glegroups.com
Subject: Re: [PATCH v3 1/2] io_uring: Move from hlist to io_wq_work_node

On 2/23/23 12:02?PM, Gabriel Krisman Bertazi wrote:
> Breno Leitao <leitao@...ian.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?

list_head is twice as big, that's the main motivation. This impacts
memory usage (obviously), but also caches when adding/removing
entries.

-- 
Jens Axboe