linux-kernel - Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem

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Date:	Mon, 22 Jun 2009 20:07:06 +0200
From:	Marco <marco.stornelli@...il.com>
To:	Pavel Machek <pavel@....cz>
CC:	Tim Bird <tim.bird@...sony.com>,
	Jamie Lokier <jamie@...reable.org>,
	Linux Embedded <linux-embedded@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Daniel Walker <dwalker@....ucsc.edu>
Subject: Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem

Pavel Machek wrote:
> On Mon 2009-06-22 10:31:28, Tim Bird wrote:
>> Pavel Machek wrote:
>>>>> How do you handle hard-links, then?
>>>> Indeed hard-links are not supported :) Due to the design of this fs
>>>> there are some limitations explained in the documentation as not
>>>> hard-link, only private memory mapping and so on. However this
>>>> limitations don't limit the fs itself because you must consider the
>>>> special goal of this fs.
>>> I did not see that in the changelog. If it is not general purpose
>>> filesystem, it is lot less interesting.
>> PRAMFS is not a general purpose filesystem. Please read
>> the introductory post to this thread, or look at
>> http://pramfs.sourceforge.net/ for more information.
> 
> Yeah, I seen that. It directly contradicts what you say.
> 

I don't think, I think it's very clear:

"In summary, PRAMFS is a light-weight, full-featured, and
space-efficient special filesystem that is ideal for systems with a
block of fast non-volatile RAM that need to access data on it using a
standard filesytem interface."


>> Since the purpose of PRAMFS is to provide a filesystem
>> that is persistent across kernel instantions, it is not
>> designed for high speed.  Robustness in the face of
>> kernel crashes or bugs is the highest priority, so
>> PRAMFS has significant overhead to make the window
>> of writability to the filesystem RAM as small as possible.
> 
> Really? So why don't you use well known, reliable fs like ext3?
> 
>> This is not a file system one would do kernel compiles on.
>> This is where someone would keep a small amount of sensitive
>> data, or crash logs that one needed to preserve over kernel
>> invocations.
> 
> Really? Web page says:
> 
> #2. If the backing-store RAM is comparable in access speed to system
> #memory, there's really no point in caching the file I/O data in the
> #page cache. Better to move file data directly between the user buffers
> #and the backing store RAM, i.e. use direct I/O. This prevents the
> #unnecessary 
> 
> So you don't cache it "because its fast", and then it is 13MB/sec?
> 
> 									Pavel
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