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 Forum index » House Training » Users ( For the regulars )
How does The Merge System, RAM and Caching/Paging? operate?
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Joined: 16 Jun 2008
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PostPosted: Fri 22 Feb 2013, 13:17    Post subject:  How does The Merge System, RAM and Caching/Paging? operate?  

Hi All,

Hopefully Devs and experienced users with technical understanding will take the time to read through and answer questions asked in this post. I've asked them only in part because of personal curiosity. I came to Puppy Linux about 5 years ago knowing almost nothing. Since then, I've learned a lot. But recently, in trying to provide some advice to a new member as a result of an experiment I just conducted I realized that I didn't really know some of the fundamentals by which Puppy operates: that I had been making assumptions. Worse, in trying to utilize a “Well-Minded Search” to locate discussions which would prove or disprove those assumptions, there appeared to be no thread which tried to tie everything together. It bad enough that I had been operating on assumptions. I'm just a user. But what if, like me, Devs building Pups and those providing technical advise also were making assumptions? So I thought it might be of value to create a thread consolidating in one place information pertaining to how Puppies interact with a computer's resources.

I recently ran a series of experiments to compare which type of application --pets, SFSes, and Program Folders-- used the least amount of my computer's resources -- RAM, SaveFile, and CPU. A Chart of my test results can be found at the bottom of http://murga-linux.com/puppy/viewtopic.php?t=84457. Examining the chart told me that I really didn't know what was happening. What did the figures in the “buffers” and “cache” columns mean?

There once was a mantra: “Puppy runs everything in RAM.” Well, maybe once when a Puppy's ISO was under 100 Mb. Currently, the minimum RAM requirements for some Pups seem to be 256 Mb to run? Load? “everything” into RAM. What is “everything?”

Examine for example, LibreOffice. When I decompressed it to create a Program Folder that folder occupied 543 Mbs of HardDrive. As an SFS using xz compression it occupied 144 Mbs of Harddrive. Installed into my SaveFile, the pet required over 500 Mbs of my SaveFile. Yet its RAM figures –-which included the use of RAM of all processes at the times-- showed up as using between 179004 Mbs and 622060 Mbs –such figures depending on which type of application I was using and whether or not it was opened and a datafile was open by it. In order to make use of a compressed application, you first have to decompress it. Decompress into what? Although the computer I was using had 3.7 Mbs of RAM, it appears that merely loading the SFS was not reported as requiring over 500 Mbs of RAM. What was not reported as RAM usage I would assume was being reported as “cached,” albeit, on my system being cached into some of the 3.7 Mbs of RAM not being counted as Memory. But you know what they say about assumptions. And suppose I didn't have more than 500 Mbs of RAM. The definition of blivot comes to mind. http://www.urbandictionary.com/define.php?term=blivot. No offense meant. Again I would assume some type of paging/caching system would be employed, and my recollection is that Puppy will use a SwapFile or SwapPartion if one is available, otherwise it would cache to a temporary folder on the HardDrive? Or is that after using available space in the SaveFile, perhaps that in the folder known as .tmp?
And how does this all tie in with the “Merge File System.” When the SFS was loaded, but not opened, links to it still appeared on the Menu. Something was obviously in RAM. [A loaded but unopened SFS appears to use less resources than even a Program Folder where, until opened, the only use of “Puppy Space” was about 140 kb creating the links to the external executables].
Again my assumption –recall caveat above-- was that on bootup Puppy first loads into RAM the operating system, then something with respect to the applications included by the Dev who created the Pup. What something? Then it load the SaveFile –or at least those links to applications installed into the SaveFile-- overwriting in RAM links to conflicting versions of applications, libraries, and settings which existed in the default Pup. Then it loads SFSes –or some (what?) portions of the SFSes-- overwriting in RAM any conflicting links, libraries, and settings previously in RAM. But as I said, I'm just guessing. What actually is taking place?
At what point in bootup does caching/paging start? My guess before was 256 Mbs. But if so –or even if not-- what factors determine what will be held in RAM, what cached and into where? Does it depend on the actual amount of RAM installed? Is it something generic to every Woof-built Pup? Is there something which a Dev creating a Pup sets?

And after bootup, when and how is the caching/paging system used? For that matter, am I confusing/misusing the terms?

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