linux-kernel - Re: [PATCH] sysctl: Add a feature to drop caches selectively

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Message-ID: <20140625221548.GA614@xo-6d-61-c0.localdomain>
Date:	Thu, 26 Jun 2014 00:15:48 +0200
From:	Pavel Machek <pavel@....cz>
To:	Thomas Knauth <thomas.knauth@....de>
Cc:	dedekind1@...il.com, David Rientjes <rientjes@...gle.com>,
	Maksym Planeta <mcsim.planeta@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sysctl: Add a feature to drop caches selectively

On Wed 2014-06-25 10:25:05, Thomas Knauth wrote:
> On Wed, Jun 25, 2014 at 8:25 AM, Artem Bityutskiy <dedekind1@...il.com> wrote:
> > Plus some explanations WRT why proc-based interface and what would be
> > the alternatives, what if tomorrow we want to extend the functionality
> > and drop caches only for certain file range, is this only for regular
> > files or also for directories, why posix_fadvice(DONTNEED) is not
> > sufficient.
> 
> I suggested the idea originally. Let me address each of your questions in turn:
> 
> Why a selective drop? To have a middle ground between echo 2 >
> drop_caches and echo 3 > drop_caches. When is this interesting? My
> particular use case was benchmarking. I wanted to repeatedly measure
> the timing when things were read from disk. Dropping everything from
> the cache, also drops useful things, not just the few files your
> benchmark intends to measure.
> 
> Why /proc? Because this is where the current drop_caches mechanism is
> located. If it should go somewhere else, please do suggest so.

It sounds like this should be a new syscall.

echoing filenames in files is strange/ugly.
										Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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