From mboxrd@z Thu Jan  1 00:00:00 1970
From: danielhilst@gmail.com (Daniel Hilst Selli)
Date: Tue, 23 Apr 2013 12:53:13 -0300
Subject: [rrd-users] Can small writes generate a lot of faults?
In-Reply-To: <9358EF77-C6D9-495B-93DE-89994A121517@oetiker.ch>
References: <5171BA2D.1040305@gmail.com>
	<9358EF77-C6D9-495B-93DE-89994A121517@oetiker.ch>
Message-ID: <5176AE69.10006@gmail.com>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

Em 20/04/2013 09:09, Tobi Oetiker escreveu:
> hi daniel
>
> On 19.04.2013, at 16:42, Daniel Hilst Selli <danielhilst@gmail.com> wrote:
>
>> AFAIK, major page faults are generated when data that is not yet present
>> on RAM is loaded from disk, but in this case data is being write do
>> disk, I can't
>> see how writes can generate faults, but still, it seems that is
>> happening, ... !?
>>
> rrdtool changes just few bytes in the rrf file with each update
>
> the OS though can only write a complete block of data to disk.
>
> so when you write a byte to a file, the OS has to first fetch the block, modify the byte and write the block back
>
> that is why rrdtool benefits greatly from more RAM as it can hold mor blocks in RAM and does not have to read them first.
>
> cheers tobi
>
Thanks Tobi, I had no idea about this read/update/write process, Now I 
know how to improve the performance of my
collectd+rrdtool stuff,

Cheers