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From: Jens Axboe <[email protected]>
To: Xiaoguang Wang <[email protected]>,
	[email protected]
Cc: [email protected]
Subject: Re: [PATCH v3] io_uring: refactor file register/unregister/update codes
Date: Tue, 31 Mar 2020 08:49:51 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 3/31/20 12:05 AM, Xiaoguang Wang wrote:
> While diving into iouring fileset resigster/unregister/update codes,
> we found one bug in fileset update codes. Iouring fileset update codes
> use a percpu_ref variable to check whether can put previous registered
> file, only when the refcnt of the perfcpu_ref variable reachs zero, can
> we safely put these files, but this do not work well. If applications
> always issue requests continually, this perfcpu_ref will never have an
> chance to reach zero, and it'll always be in atomic mode, also will
> defeat the gains introduced by fileset register/unresiger/update feature,
> which are used to reduce the atomic operation overhead of fput/fget.
> 
> To fix this issue, while applications do IORING_REGISTER_FILES or
> IORING_REGISTER_FILES_UPDATE operations, we allocate a new percpu_ref
> and kill the old percpu_ref, new requests will use the new percpu_ref.
> Once all previous old requests complete, old percpu_refs will be dropped
> and registered files will be put safely.

Looks good to me! This is a nice improvement, applied for 5.7. Thanks.

-- 
Jens Axboe


      reply	other threads:[~2020-03-31 14:49 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-31  6:05 [PATCH v3] io_uring: refactor file register/unregister/update codes Xiaoguang Wang
2020-03-31 14:49 ` Jens Axboe [this message]

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