Re: Question about sendfile

From: Pavel Begunkov <asml.silence@gmail.com>
To: Hao Xu <haoxu@linux.alibaba.com>
Cc: Jens Axboe <axboe@kernel.dk>, io-uring <io-uring@vger.kernel.org>,
	Joseph Qi <joseph.qi@linux.alibaba.com>
Subject: Re: Question about sendfile
Date: Wed, 7 Jul 2021 15:16:29 +0100	[thread overview]
Message-ID: <4831bcfd-ce4a-c386-c5b2-a1417a23c500@gmail.com> (raw)
In-Reply-To: <6a7ceb04-3503-7300-8089-86c106a95e96@linux.alibaba.com>

On 7/3/21 11:47 AM, Hao Xu wrote:
> Hi Pavel,
> I found this mail about sendfile in the maillist, may I ask why it's not
> good to have one pipe each for a io-wq thread.
> https://lore.kernel.org/io-uring/94dbbb15-4751-d03c-01fd-d25a0fe98e25@gmail.com/

IIRC, it's one page allocated for each such task, which is bearable but
don't like yet another chunk of uncontrollable implicit state. If there
not a bunch of active workers, IFAIK there is no way to force them to
drop their pipes.

I also don't remember the restrictions on the sendfile and what's with
the eternal question of "what to do if the write part of sendfile has
failed".   

Though, workers are now much more alike to user threads, so there
should be less of concern. And even though my gut feeling don't like
them, it may actually be useful. Do you have a good use case where
explicit pipes don't work well? 

-- 
Pavel Begunkov