linux-kernel - Re: [RFC v7] wait: prevent exclusive waiter starvation

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Message-ID: <20090129044227.GA5231@redhat.com>
Date:	Thu, 29 Jan 2009 05:42:27 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Matthew Wilcox <matthew@....cx>,
	Chuck Lever <cel@...i.umich.edu>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC v7] wait: prevent exclusive waiter starvation

On 01/28, Johannes Weiner wrote:
>
> Add abort_exclusive_wait() which removes the process' wait descriptor
> from the waitqueue, iff still queued, or wakes up the next waiter
> otherwise.  It does so under the waitqueue lock.  Racing with a wake
> up means the aborting process is either already woken (removed from
> the queue) and will wake up the next waiter, or it will remove itself
> from the queue and the concurrent wake up will apply to the next
> waiter after it.
>
> Use abort_exclusive_wait() in __wait_event_interruptible_exclusive()
> and __wait_on_bit_lock() when they were interrupted by other means
> than a wake up through the queue.

Imho, this all is right, and this patch should replace
lock_page_killable-avoid-lost-wakeups.patch (except for stable tree).

But I guess we need maintainer's opinion, we have them in cc ;)

Oleg.

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