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Tired of explaining Linux's seemingly obtuse memory usage to confused newbies?

linuxatemyram.com

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Re: Tired of explaining Linux's seemingly obtuse memory usage to confused newbies?

#31

Post by colanderman »

kindlyviking wrote: post #25
colanderman wrote: post #21

This is misleading, as the kernel will often swap out processes rather than shrink the disk cache. Its tendency to do this is controlled by the vm.swappiness parameter, which by default heavily favors swapping: http://kerneltrap.org/node/3000 Decreasing this value will favor reducing the cache size and will tend to increase responsiveness. You can set it in the /etc/sysctl.conf file. Low values (≤ 5) are especially g…

The article mentions this on the second page at the bottom: http://www.linuxatemyram.com/play.html

"But look you found the notice didn't you?"

"Yes," said Arthur, "yes I did. It was on display in the bottom of a locked filing cabinet stuck in a disused lavatory with a sign on the door saying 'Beware of The Leopard'."

Re: Tired of explaining Linux's seemingly obtuse memory usage to confused newbies?

#32

Post by [deleted] »

colanderman wrote: post #21

This is misleading, as the kernel will often swap out processes rather than shrink the disk cache. Its tendency to do this is controlled by the vm.swappiness parameter, which by default heavily favors swapping: http://kerneltrap.org/node/3000 Decreasing this value will favor reducing the cache size and will tend to increase responsiveness. You can set it in the /etc/sysctl.conf file. Low values (≤ 5) are especially g…

[deleted]

Re: Tired of explaining Linux's seemingly obtuse memory usage to confused newbies?

#34

Post by hernan7 »

wzdd wrote: post #26

This paragraph: 'But what do you call memory that is both used for something and available for applications? You would call that "free", but Linux calls it "used".' is IMO the best way I've ever seen of explaining the issue. It also reveals the solution: call it free! It is free, after all. Nobody cares about how much free ram is cache unless they are doing something really specific, in which case they should be pass…

Maybe add a new (end user-friendly, preferably graphical) tool to report memory usage the user friendly way? Then vmstat can be left as is, and end users can be directed to use the new tool.

By the way, this behavior is not Linux-specific. AIX and other Unices have been doing this forever. And end users (who should have known better, BTW) would complain too. The only machine that I remember as showing a sizable percentage of the memory as "free" was a just-imaged top of the line server. Half a gig or RAM, and almost all empty! -- this was the early '90s.

Edit: Just noticed that graphical tools that report memory usage in user-friendly terms already exist (gnome system monitor). My bad, I always use vmstat and sar myself, and only recently found out about /proc/NNNNN/status

Re: Tired of explaining Linux's seemingly obtuse memory usage to confused newbies?

#35

Post by NonMint »

ktf wrote: post #33

It looks like gnome-system-monitor reports the "correct" amount of free RAM. I'd imagine most newbies would use that rather than popping open a terminal and typing "free," right?

You'd be surprised. Some users who use Linux consider themselves to be pretty adept, and I can easily see this problem being an issue for people who perceive themselves to be clever.

Re: Tired of explaining Linux's seemingly obtuse memory usage to confused newbies?

#37

Post by wrs »

wzdd wrote: post #26

This paragraph: 'But what do you call memory that is both used for something and available for applications? You would call that "free", but Linux calls it "used".' is IMO the best way I've ever seen of explaining the issue. It also reveals the solution: call it free! It is free, after all. Nobody cares about how much free ram is cache unless they are doing something really specific, in which case they should be pass…

Or just rename "free" to "wasted". I usually tell people the free number indicates how much RAM they paid for but aren't using.

Re: Tired of explaining Linux's seemingly obtuse memory usage to confused newbies?

#38

Post by requinot59 »

jerf wrote: post #30
colanderman wrote: post #21

This is misleading, as the kernel will often swap out processes rather than shrink the disk cache. Its tendency to do this is controlled by the vm.swappiness parameter, which by default heavily favors swapping: http://kerneltrap.org/node/3000 Decreasing this value will favor reducing the cache size and will tend to increase responsiveness. You can set it in the /etc/sysctl.conf file. Low values (≤ 5) are especially g…

I often just turn swap off entirely. A normal workload on my 4GB linux machine will frequently fail to fill even 2GB of buffers . At the moment my machine has still managed to fail to fill 800MB of my RAM with anything and I'm running two virtual machines and doing my usual work load. I do have a swap partition but only so I can hibernate.

> I often just turn swap off entirely.

And you're smart to do so. Swap is useless for 99% of end-user systems. ChromeOS doesn't use any swap partition, for instance.

As for hibernation, it's not available if you use a crypted swap, which is wise to use (at least on a laptop).

As a result, I, too, disabled swap completely.

Re: Tired of explaining Linux's seemingly obtuse memory usage to confused newbies?

#40

Post by radu_floricica »

I have had the same problem, plus some, when trying to guesstimate memory usage in vps servers. The caching is transparent, so free always reports zero swap. ps gives sensible numbers, but the total used memory is neither RSS nor VSZ summed. I've heard about library memory being double-counted, but I've found no way to accurately get the numbers. In the end I pretty much gave up and settled for the settings that worked.

tl;dr: on vps things can be even uglier.

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