linux-kernel - Re: io_pgetevents & aio fsync V2

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Message-ID: <20180406031630.GU30522@ZenIV.linux.org.uk>
Date:   Fri, 6 Apr 2018 04:16:30 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Christoph Hellwig <hch@....de>
Cc:     Avi Kivity <avi@...lladb.com>, linux-aio@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: io_pgetevents & aio fsync V2

On Wed, Mar 28, 2018 at 09:26:33AM +0200, Christoph Hellwig wrote:
> Hi all,
> 
> this patch adds workqueue based fsync offload.  Version of this
> patch have been floating around for a couple years, but we now
> have a user with seastar used by ScyllaDB (who sponsored this
> work) that really wants this in addition to the aio poll support.
> More details are in the patch itself.
> 
> Because the iocb types have been defined sine day one (and probably
> were supported by RHEL3) libaio already supports these calls as-is.
> 
> This also pulls in the aio cleanups and io_pgetevents support previously
> submitted and review as part of the aio poll series.  The aio poll
> series will be resubmitted on top of this series

BTW, this is only tangentially related, but... does *anything* call
io_submit() for huge amounts of iocb?  Check in do_io_submit() is
insane - "no more than MAX_LONG total of _pointers_".  Compat variant
goes for "no more than a page worth of pointers" and there's
a hard limit in ioctx_alloc() - we can't ever get more than
8M slots in ring buffer...