From: Artem Bityutskiy <dedekind1@gmail.com>
To: Thomas Knauth <thomas.knauth@gmx.de>
Cc: David Rientjes <rientjes@google.com>,
Maksym Planeta <mcsim.planeta@gmail.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sysctl: Add a feature to drop caches selectively
Date: Wed, 25 Jun 2014 12:56:24 +0300 [thread overview]
Message-ID: <1403690184.20275.11.camel@sauron.fi.intel.com> (raw)
In-Reply-To: <CABhLV03_PNFiwsvt+yitcsKxz5TeVECCFavdNkbgQ+XzQqASaw@mail.gmail.com>
On Wed, 2014-06-25 at 10:25 +0200, Thomas Knauth wrote:
> On Wed, Jun 25, 2014 at 8:25 AM, Artem Bityutskiy <dedekind1@gmail.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:
Thanks for the answer, although you forgot to comment on the question
about possibly extending the new interface to work with file ranges in
the future. For example, I have a 2 TiB file, and I am only interested
in dropping caches for the first couple of gigabytes. Would I extend
your interface, or would I come up with another one?
> 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.
Sounds like a reasonable motivation for me.
> Why /proc? Because this is where the current drop_caches mechanism is
> located. If it should go somewhere else, please do suggest so.
I do not have particular suggestions, just pulling the information about
how much efforts were put into choosing the interface.
> Why not use posix_fadvice()? Because it is exactly this, an advice.
> The kernel is free to do whatever, i.e., also ignore the request. We
> want a mechanism that reliably drops select content from the cache.
OK, thanks.
--
Best Regards,
Artem Bityutskiy
next prev parent reply other threads:[~2014-06-25 9:56 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-24 16:10 [PATCH] sysctl: Add a feature to drop caches selectively Maksym Planeta
2014-06-24 21:59 ` David Rientjes
2014-06-25 6:25 ` Artem Bityutskiy
2014-06-25 8:25 ` Thomas Knauth
2014-06-25 9:56 ` Artem Bityutskiy [this message]
2014-06-25 13:23 ` Thomas Knauth
2014-06-25 13:30 ` Artem Bityutskiy
2014-06-25 13:42 ` Artem Bityutskiy
2014-06-26 9:30 ` Maksym Planeta
2014-06-25 10:03 ` Artem Bityutskiy
2014-06-25 13:19 ` Thomas Knauth
2014-06-25 22:15 ` Pavel Machek
2014-06-26 1:06 ` Dave Chinner
2014-06-26 6:13 ` Artem Bityutskiy
2014-06-26 10:36 ` Bernd Schubert
2014-06-26 11:31 ` Artem Bityutskiy
2014-06-26 11:57 ` Lukáš Czerner
2014-06-26 12:10 ` Bernd Schubert
2014-06-27 2:55 ` Dave Chinner
2014-06-27 8:58 ` Bernd Schubert
2014-06-27 8:41 ` Matthias Schniedermeyer
2014-06-27 9:04 ` Lukáš Czerner
2014-06-27 9:08 ` Artem Bityutskiy
2014-06-27 9:09 ` Bityutskiy, Artem
2014-06-27 2:48 ` Dave Chinner
[not found] <CACVxJT_6sp=KDy=jCNBypYapKv_59W8LxFU4OiJEm6gt_SuZKg@mail.gmail.com>
2014-06-25 11:21 ` Alexey Dobriyan
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