From: Tejun Heo <tj@kernel.org>
To: Kent Overstreet <koverstreet@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>,
srivatsa.bhat@linux.vnet.ibm.com, rusty@rustcorp.com.au,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] generic dynamic per cpu refcounting
Date: Mon, 28 Jan 2013 13:50:42 -0800 [thread overview]
Message-ID: <20130128215042.GN22465@mtj.dyndns.org> (raw)
In-Reply-To: <20130128214506.GG26407@google.com>
Hello, Kent.
On Mon, Jan 28, 2013 at 01:45:06PM -0800, Kent Overstreet wrote:
> Ahh. Bias value sounds... hacky (i.e. harder to convince myself it's
> correct) but I see what you're getting at.
I don't think it's that hacky. Just push the base point to the
opposite of zero - LLONG_MAX. The global counter can start biased so
that it gets unbiased only once dying is confirmed and everything can
blindly do atomic64_dec_and_test() and trust the result.
> Something to consider is wrapping; after we set state to dying but
> before we've collected the percpu counters, the atomic counter may be
> negative.
There's a reason why we use 64bit vars for this type of global
counting. They virtually don't wrap. Here, you'll need 1<<63 for the
counter to unintentionally reach 0, which we consider practically
impossible.
Thanks.
--
tejun
next prev parent reply other threads:[~2013-01-28 21:50 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20130124232024.GA584@google.com>
2013-01-25 18:09 ` Oleg Nesterov
2013-01-25 18:29 ` Oleg Nesterov
2013-01-28 18:10 ` Kent Overstreet
2013-01-28 18:50 ` Oleg Nesterov
2013-01-25 19:11 ` Oleg Nesterov
2013-01-28 18:15 ` Kent Overstreet
2013-01-28 18:27 ` Tejun Heo
2013-01-28 18:49 ` Kent Overstreet
2013-01-28 18:55 ` Tejun Heo
2013-01-28 20:22 ` Kent Overstreet
2013-01-28 20:27 ` Tejun Heo
2013-01-28 20:55 ` Kent Overstreet
2013-01-28 21:18 ` Tejun Heo
2013-01-28 21:24 ` Kent Overstreet
2013-01-28 21:28 ` Tejun Heo
2013-01-28 21:36 ` Tejun Heo
2013-01-28 21:48 ` Kent Overstreet
2013-01-28 21:45 ` Kent Overstreet
2013-01-28 21:50 ` Tejun Heo [this message]
2013-01-29 16:39 ` Kent Overstreet
2013-01-29 19:29 ` Tejun Heo
2013-01-29 19:51 ` Kent Overstreet
2013-01-29 20:02 ` Tejun Heo
2013-01-29 21:45 ` Kent Overstreet
2013-01-29 22:06 ` Tejun Heo
2013-01-29 18:04 ` [PATCH] module: Convert to generic percpu refcounts Kent Overstreet
2013-01-28 18:07 ` [PATCH] generic dynamic per cpu refcounting Kent Overstreet
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