linux-ext4 - Re: [PATCH 0/8 v2] Non-blocking AIO

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Message-ID: <20170306082546.GA14932@quack2.suse.cz>
Date:   Mon, 6 Mar 2017 09:25:46 +0100
From:   Jan Kara <jack@...e.cz>
To:     Avi Kivity <avi@...lladb.com>
Cc:     Goldwyn Rodrigues <rgoldwyn@...e.de>, jack@...e.com,
        hch@...radead.org, linux-fsdevel@...r.kernel.org,
        linux-block@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org
Subject: Re: [PATCH 0/8 v2] Non-blocking AIO

On Sun 05-03-17 16:56:21, Avi Kivity wrote:
> >The goal of the patch series is to return -EAGAIN/-EWOULDBLOCK if
> >any of these conditions are met. This way userspace can push most
> >of the write()s to the kernel to the best of its ability to complete
> >and if it returns -EAGAIN, can defer it to another thread.
> >
> 
> Is it not possible to push the iocb to a workqueue?  This will allow
> existing userspace to work with the new functionality, unchanged. Any
> userspace implementation would have to do the same thing, so it's not like
> we're saving anything by pushing it there.

That is not easy because until IO is fully submitted, you need some parts
of the context of the process which submits the IO (e.g. memory mappings,
but possibly also other credentials). So you would need to somehow transfer
this information to the workqueue.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR