linux-kernel - Re: [PATCH] fs: fput() can be called from interrupt context

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Message-ID: <alpine.DEB.1.10.0903140729060.26556@makko.or.mcafeemobile.com>
Date:	Sat, 14 Mar 2009 07:32:19 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Trond Myklebust <trond.myklebust@....uio.no>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <dada1@...mosbay.com>,
	Jeff Moyer <jmoyer@...hat.com>, Avi Kivity <avi@...hat.com>,
	linux-aio <linux-aio@...ck.org>, zach.brown@...cle.com,
	Benjamin LaHaise <bcrl@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH] fs: fput() can be called from interrupt context

On Sat, 14 Mar 2009, Trond Myklebust wrote:

> > Did I miss something? This wouldn't be (eventually) on keventd shoulders, 
> > but on aio work queue (aio_wq).
> > I guess we could do the same optimization we're already doing for ki_filp, 
> > for ki_eventfd ...
> 
> Last I checked, a call to schedule_work(&fddef->wq) would still run
> fd_defer_queue() under keventd.

Oh, you were commenting about Eric's patch-set. I thought you were talking 
about the current status (that my reply to Andrew was hinting to), and was 
wondering for a while from where fd_defer_queue() came from.

> That said, even if you were to run it under aio_wq, the argument remains
> the same: do you really want to add potentially long lasting sleeps onto
> a work queue that was designed to service fast i/o requests?

No, and if you roll back, you couldn't miss to notice that mine was a 
question about the f_count direct manipulation/optimization. We can do the 
same optimization for eventfd, although both will fall in the aio kthread 
in any case, if we're holding the last insteance of the file* (that I 
guess we can consider an unlikely case).
Dunno how worth it could be adding a new NCPU*thread(s) just to handle 
delayed fputs.

- Davide

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