linux-kernel - Re: [PATCH] writeback: remove unnecessary wait in throttle_vm

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Message-ID: <y0mabr6vabt.fsf@ton.toronto.redhat.com>
Date:	Fri, 28 Sep 2007 15:50:14 -0400
From:	fche@...hat.com (Frank Ch. Eigler)
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Fengguang Wu <wfg@...l.ustc.edu.cn>,
	hirofumi@...l.parknet.co.jp, galak@...nel.crashing.org,
	zaitcev@...hat.com, greg@...ah.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, mbligh@...gle.com
Subject: Re: [PATCH] writeback: remove unnecessary wait in throttle_vm_writeout()


Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> writes:

>> [...]
>> > I totally agree with Ingo here. Having a basic instrumentation that is
>> > enabled by default will help to identify code paths causing unexpected
>> > delays in the kernel. [...]
>
>> It is. See: CONFIG_VM_EVENT_COUNTERS and all the other vm specific
>> crap littered in /proc/ (buddyinfo, zoneinfo, meminfo, etc).  [...]

> Isn't the actual instrumentation present in the VM subsystem
> consisting mostly of event counters ? This kind of profiling
> provides limited help in following specific delays in the
> kernel. [...]

These existing VM events/counters could be a good target for a second
worked-out example (after blktrace) of reimplementation using generic
markers.

- FChE
-
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