From: Johannes Stezenbach <js@sig21.net>
To: dave b <db.pub.mail@gmail.com>
Cc: Florian Mickler <florian@mickler.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org
Subject: Re: block cache replacement strategy?
Date: Mon, 13 Sep 2010 21:26:26 +0200 [thread overview]
Message-ID: <20100913192626.GA15092@sig21.net> (raw)
In-Reply-To: <AANLkTikoUAgRV18axesaiYnpBWe2V-xhALgh7dtF7p3Y@mail.gmail.com>
On Tue, Sep 14, 2010 at 05:09:31AM +1000, dave b wrote:
> On 14 September 2010 01:21, Johannes Stezenbach <js@sig21.net> wrote:
> > On Fri, Sep 10, 2010 at 06:02:48PM +0200, Johannes Stezenbach wrote:
> >>
> >> Linear read heuristic might be a good guess, but it would
> >> be nice to hear a comment from a vm/fs expert which
> >> confirms this works as intended.
> >
> > Anyway I found lmdd (from lmbench) can do random reads,
> > and indeed causes the data to enter the block (page?) cache,
> > replacing the previous data.
>
> I am no expert, but what did you think would happen if you did dd
> twice from /dev/zero?
> but... Honestly what do you think will be cached?
It's not from /dev/zero, it is from file to /dev/null.
It all started with me wanting to compare disk read bandwidth
vs. read bandwidth of my root partition via dm-crypt + LVM,
and then wondering why dd from raw disk seemed to be
cached while dd from crypted root partition didn't.
Johannes
WARNING: multiple messages have this Message-ID (diff)
From: Johannes Stezenbach <js@sig21.net>
To: dave b <db.pub.mail@gmail.com>
Cc: Florian Mickler <florian@mickler.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org
Subject: Re: block cache replacement strategy?
Date: Mon, 13 Sep 2010 21:26:26 +0200 [thread overview]
Message-ID: <20100913192626.GA15092@sig21.net> (raw)
In-Reply-To: <AANLkTikoUAgRV18axesaiYnpBWe2V-xhALgh7dtF7p3Y@mail.gmail.com>
On Tue, Sep 14, 2010 at 05:09:31AM +1000, dave b wrote:
> On 14 September 2010 01:21, Johannes Stezenbach <js@sig21.net> wrote:
> > On Fri, Sep 10, 2010 at 06:02:48PM +0200, Johannes Stezenbach wrote:
> >>
> >> Linear read heuristic might be a good guess, but it would
> >> be nice to hear a comment from a vm/fs expert which
> >> confirms this works as intended.
> >
> > Anyway I found lmdd (from lmbench) can do random reads,
> > and indeed causes the data to enter the block (page?) cache,
> > replacing the previous data.
>
> I am no expert, but what did you think would happen if you did dd
> twice from /dev/zero?
> but... Honestly what do you think will be cached?
It's not from /dev/zero, it is from file to /dev/null.
It all started with me wanting to compare disk read bandwidth
vs. read bandwidth of my root partition via dm-crypt + LVM,
and then wondering why dd from raw disk seemed to be
cached while dd from crypted root partition didn't.
Johannes
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next prev parent reply other threads:[~2010-09-13 19:26 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-07 13:34 block cache replacement strategy? Johannes Stezenbach
2010-09-07 13:34 ` Johannes Stezenbach
2010-09-09 12:00 ` Johannes Stezenbach
2010-09-09 12:00 ` Johannes Stezenbach
2010-09-10 10:02 ` Florian Mickler
2010-09-10 10:02 ` Florian Mickler
2010-09-10 16:02 ` Johannes Stezenbach
2010-09-10 16:02 ` Johannes Stezenbach
2010-09-13 15:21 ` Johannes Stezenbach
2010-09-13 15:21 ` Johannes Stezenbach
2010-09-13 19:09 ` dave b
2010-09-13 19:09 ` dave b
2010-09-13 19:26 ` Johannes Stezenbach [this message]
2010-09-13 19:26 ` Johannes Stezenbach
2010-09-30 23:27 ` Jan Kara
2010-09-30 23:27 ` Jan Kara
2010-10-01 13:05 ` Johannes Stezenbach
2010-10-01 13:05 ` Johannes Stezenbach
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