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From: Pavel Begunkov <>
To: Hao Xu <>, Jens Axboe <>
Cc:, Joseph Qi <>
Subject: Re: [PATCH] io_uring: don't free request to slab
Date: Wed, 25 Aug 2021 17:02:03 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 8/25/21 4:38 PM, Hao Xu wrote:
> 在 2021/8/25 下午9:28, Pavel Begunkov 写道:
>> On 8/25/21 12:40 PM, Hao Xu wrote:
>>> It's not neccessary to free the request back to slab when we fail to
>>> get sqe, just update state->free_reqs pointer.
>> It's a bit hackish because depends on the request being drawn
>> from the array in a particular way. How about returning it
> It seems a req is always allocated from state->reqs, so it should be
> ok? I actually didn't understand 'hackish' here, do you mean
> io_submit_sqes() shouldn't move state->free_reqs which is req caches'
> internal implementation?

I mean it uses implicit knowledge of how io_alloc_req() works, which
may and actually will change. It's just always too easy to forget
about that little one-off thing while changing another chunk.

To give an example, if one decides to remake it and first serve
requests from state->free_list and only when it's empty look into
state->reqs, it's too easy to forget opening a pretty severe

If there is not much profit from it comparing to the risks, I'd
personally prefer to go with a safer way.  

>> into state->free_list. That thing is as cold as it can get,
>> only buggy apps can hit it.

Pavel Begunkov

      reply	other threads:[~2021-08-25 16:03 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-25 11:40 [PATCH] io_uring: don't free request to slab Hao Xu
2021-08-25 13:28 ` Pavel Begunkov
2021-08-25 15:38   ` Hao Xu
2021-08-25 16:02     ` Pavel Begunkov [this message]

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