From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Stezenbach Subject: Re: block cache replacement strategy? Date: Mon, 13 Sep 2010 21:26:26 +0200 Message-ID: <20100913192626.GA15092@sig21.net> References: <20100907133429.GB3430@sig21.net> <20100909120044.GA27765@sig21.net> <20100910120235.455962c4@schatten.dmk.lab> <20100910160247.GA637@sig21.net> <20100913152138.GA16334@sig21.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Florian Mickler , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org To: dave b Return-path: Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Tue, Sep 14, 2010 at 05:09:31AM +1000, dave b wrote: > On 14 September 2010 01:21, Johannes Stezenbach 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org