From: Peter Hurley <peter@hurleysoftware.com>
To: Andi Kleen <andi@firstfloor.org>, Lin Ming <minggr@gmail.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>,
Greg KH <gregkh@linuxfoundation.org>,
LKML <linux-kernel@vger.kernel.org>,
lkp@01.org, Tejun Heo <tj@kernel.org>
Subject: Re: increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty_data"
Date: Thu, 26 Sep 2013 07:52:23 -0400 [thread overview]
Message-ID: <52441FF7.1030405@hurleysoftware.com> (raw)
In-Reply-To: <87r4cc8e0q.fsf@tassilo.jf.intel.com>
On 09/25/2013 11:20 PM, Andi Kleen wrote:
> Lin Ming <minggr@gmail.com> writes:
>>
>> Would you like below patch?
>
> The loop body keeps rather complex state. It could easily
> get confused by parallel RCU changes.
>
> So if the list changes in parallel you may suddenly
> report very bogus values, as the va_start - prev_end
> computation may be bogus.
>
> Perhaps it's ok (may report bogus gaps), but it seems a bit risky.
I don't understand how the computed gap would be bogus; there
_was_ a list state in which that particular gap existed. The fact
that it may not exist anymore can also happen in the existing
algorithm the instant get_vmalloc_info() drops the vmap_area_lock.
OTOH, parallel list changes could cause an rcu-based get_vmalloc_info()
to over-report or under-report used memory due to parallel list
changes.
If this is a problem in practice, then usage and largest chunk
should be tracked by the allocator instead, obviating the need for
get_vmalloc_info() to traverse the vmap_area_list at all.
Regards,
Peter Hurley
next prev parent reply other threads:[~2013-09-26 11:52 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-13 0:51 increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty_data" Fengguang Wu
2013-09-13 1:09 ` Fengguang Wu
2013-09-17 15:34 ` Peter Hurley
2013-09-17 23:22 ` Fengguang Wu
2013-09-18 0:22 ` Peter Hurley
2013-09-25 9:04 ` Lin Ming
2013-09-25 11:30 ` Peter Hurley
2013-09-25 14:53 ` Lin Ming
2013-09-25 16:02 ` Lin Ming
2013-09-26 3:20 ` Andi Kleen
2013-09-26 11:52 ` Peter Hurley [this message]
2013-09-26 15:32 ` Andi Kleen
2013-09-26 17:22 ` Peter Hurley
2013-09-26 7:33 ` Andrew Morton
2013-09-26 11:31 ` Peter Hurley
2013-09-26 15:04 ` Greg KH
2013-09-26 17:35 ` Peter Hurley
2013-09-26 18:05 ` Andrew Morton
2013-09-26 21:42 ` Peter Hurley
2013-09-26 21:58 ` Andrew Morton
2013-09-26 22:21 ` Peter Hurley
2013-09-18 0:49 ` Peter Hurley
2013-09-13 3:17 ` Greg KH
2013-09-13 3:38 ` Fengguang Wu
2013-09-13 3:44 ` Greg KH
2013-09-13 9:55 ` Peter Hurley
2013-09-13 12:34 ` Greg KH
2013-09-17 2:42 ` Peter Hurley
2013-09-17 2:56 ` Fengguang Wu
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