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Something is deeply broken in OS X memory management

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Re: Something is deeply broken in OS X memory management

#21

Post by microtonal »

gurkendoktor wrote: post #8
w0utert wrote: post #4

Not this again, we already went through this a few weeks ago. Back then, I thought the conclusion was that there is nothing broken about OS X memory management, and that with every 'fix' you come up with, you will just introduce another degenerate corner case. The same holds for any OS, trade-offs are made that may have some negative effect in some cases, to the benefit of the general cases. I don't recognize any of…

The thing is, Lion runs like crap without an SSD or insane amounts of RAM for many people. It doesn't help if it works for some, or even the majority. If anything, we need more people digging in OS X internals. I am sorry to use a tired analogy here, but Vista did work great for many too. I have two Macs, one brand new, one migrated from SL, and 10.7 Safari was almost unusable on both until I installed SSDs. If that…

I have the same experience: my MBP with 8GB RAM and SSD is pretty fast running Lion. But my two-year old Mac Mini at work with 4GB and platter disk runs terribly slow ever since I did a clean Lion install.

Re: Something is deeply broken in OS X memory management

#22

Post by obituary_latte »

w0utert wrote: post #4

Not this again, we already went through this a few weeks ago. Back then, I thought the conclusion was that there is nothing broken about OS X memory management, and that with every 'fix' you come up with, you will just introduce another degenerate corner case. The same holds for any OS, trade-offs are made that may have some negative effect in some cases, to the benefit of the general cases. I don't recognize any of…

>I don't recognize any of his symptoms anyway, and my OS X computers get pretty RAM-heavy use, with almost always a linux VM open, XCode, Safari with ~10 tabs, iTunes with a few thousand songs, etc.

Oh boy I wish I could say the same. Admittedly I don't shut down on a daily basis but this didn't used to be a problem in SL. FWIW I've an old tank of a tower that has a video card on its last leg.. shutting down invariably leads to ~30 minutes of downtime while the card heats up and reconnects whatever needs reconnecting for both monitors to work.

Since Lion, I've noticed frequent hangs and beach-balls when doing even menial tasks. Transmit, terminal, texmate, a few tabs in chrome. If time machine starts backing up I can forget about a smooth Preview open or switching to a largish open textmate file without beach-ball'ing. If I want to use a Win7 Parallels VM--I can't do anything else. Even now as I type this I have a ubuntu vm running at the login screent and it causes the machine to shake off the cobwebs between almost everything.

It's certainly not a bad machine--there's 8gb ram, and tons of diskspace--good processor. In fact, I would go multiple months without a reboot and heavy use when on SL without hardly any problems at all.

Then there is the new i5 MBPro. Cool trick you can do: hook up an external monitor via thunderbolt and watch as the [left side] dock becomes a mangled mess with icons miss-positioned and wrongly triggering apps--it's like playing a game of whack-a-mole trying to open terminal to kill -KILL dock :)

The i5 has also been less than stellar compared to the older MBPro I sold to buy it in terms of performance.

Re: Something is deeply broken in OS X memory management

#23

Post by merlish »

w0utert wrote: post #4

Not this again, we already went through this a few weeks ago. Back then, I thought the conclusion was that there is nothing broken about OS X memory management, and that with every 'fix' you come up with, you will just introduce another degenerate corner case. The same holds for any OS, trade-offs are made that may have some negative effect in some cases, to the benefit of the general cases. I don't recognize any of…

I see the same issues the guy in the article has seen. Basically, I have a total of 8GB of ram in this here mac mini, and when my desktop session gets heavy things start going south.

For example: Let's take a large Chrome session (~150 tabs spread over several windows), an IDE open somewhere, Spotify, Steam and some background apps, and a small Windows VM. Generally, Activity Monitor would show that Chrome in this instance would be eating 2-3GB of RAM, the VM would be eating 1GB + change of unpageable ('wired') memory, the random utils & spotify & steam & ide du jour & crap would eat another 1.5GB or so, and, long story short, there's very little 'free' memory left (think 1GB of 'Inactive' memory.

Everyone agrees that Inactive memory should be freed when more memory is required by the system and we're out of Free. My own limited testing shows instead that opening more tabs during normal use to the point where the Free memory is consumed instead results in massive delays across the system as memory is paged out to disk, and the Inactive memory doesn't seem to noticeably change in size.

I don't really know what it's doing, but it will consistently make the system very unpleasant to use for a good 30 seconds until the hard disk stops clicking. (It's unpleasant enough that I try to limit my browser session sizes now, and only run the VM when I need to.)

Re: Something is deeply broken in OS X memory management

#24

Post by spudlyo »

w0utert wrote: post #4

Not this again, we already went through this a few weeks ago. Back then, I thought the conclusion was that there is nothing broken about OS X memory management, and that with every 'fix' you come up with, you will just introduce another degenerate corner case. The same holds for any OS, trade-offs are made that may have some negative effect in some cases, to the benefit of the general cases. I don't recognize any of…

I don't recognize any of his symptoms anyway, and my OS X computers get pretty RAM-heavy use, with almost always a linux VM open, XCode, Safari with ~10 tabs, iTunes with a few thousand songs, etc.

I think you missed a key ingredient to this problem, which is heavy disk reads caused by either spotlight or time machine.

Reading a massive amount of data (that you'll probably not use again anytime soon) has the unfortunate side effect of polluting the disk cache with junk. Now if OSX is anything like Linux in this regard, it is loathe to toss out old disk cache (in response to all the incoming junk it's being asked to cache) and will instead start swapping to free up more memory for disk cache.

Linux has /proc/sys/vm/swappiness to control how aggressive it will be in swapping stuff out to preserve precious buffer cache, but I don't think OSX has any such mechanism.

Re: Something is deeply broken in OS X memory management

#25

Post by fromhet »

sabat wrote: post #11
collint wrote: post #2

You can run `purge` in a terminal to free your 'inactive' ram. I've set up a cron job to purge frequently, keeps thing humming.

Cmd line syntax, for the lazy, please?

I made a bash script for it and I'll share it, hacker 2 hacker. Goes a little something like this:

#!/bin/bash

purge

Re: Something is deeply broken in OS X memory management

#27

Post by nchuhoai »

bsimpson wrote: post #17

I've been a Mac user since the beginning, and by far my biggest frustration is the perpetual running-out-of-RAM, even when I close basically everything. I have 4GB of RAM, and frequently catch kernel_task using at least half of it.

Seriously, I have the same problem

Re: Something is deeply broken in OS X memory management

#28

Post by hollerith »

w0utert wrote: post #4

Not this again, we already went through this a few weeks ago. Back then, I thought the conclusion was that there is nothing broken about OS X memory management, and that with every 'fix' you come up with, you will just introduce another degenerate corner case. The same holds for any OS, trade-offs are made that may have some negative effect in some cases, to the benefit of the general cases. I don't recognize any of…

>we already went through this a few weeks ago. . . . Back then, I thought the conclusion was that there is nothing broken about OS X memory management

I read through the comment of a few weeks ago, and I did not see anything conclusive or even anything that would outweigh my subjective impressions that something about Lion on my (stock) 2011 Mac mini is causing unnecessary lack of responsiveness.

You might be uncomfortable with subjective impressions and many pieces of weak evidence, but given the popularity of OS X on this site, not all of us want to wait for what you refer to as "hard facts" before engaging in a discussion of the issue.

Re: Something is deeply broken in OS X memory management

#29

Post by fromhet »

bsimpson wrote: post #17

I've been a Mac user since the beginning, and by far my biggest frustration is the perpetual running-out-of-RAM, even when I close basically everything. I have 4GB of RAM, and frequently catch kernel_task using at least half of it.

Isn't there anything to do about kernel_task using up so much memory? Since it's nonfree, is apple planning on doing anything about this?

Re: Something is deeply broken in OS X memory management

#30

Post by kevingadd »

munin wrote: post #16

the OS X kernel is open source. so why aren't people reading it to figure out where this bug is?

Yeah, I'm sure if you just read the Darwin kernel there's a '#define USE_LOTS_OF_MEMORY 1' in there that you can change.

The class of problems described in the original post are not the sort of thing you 'just find' by glancing at kernel source code. The problems described sound like they could be an issue of poorly tuned heuristics/thresholds, or necessitate some extra machinery inside the OS X memory manager that isn't there currently. It's not like you can send Apple a pull request on github.

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