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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

#81

Post by netnichols »

thought_alarm wrote: post #59
carguy1983 wrote: post #51

I have an 8-way Xeon Mac Pro w/ 20GB of RAM, almost half of which is 'free' at any point during the day unless I'm doing something really out of the ordinary. Yet it still swaps to disk ALL THE TIME and a new Terminal.app window can take up to 5 seconds to open. I really don't give a shit how it's not "technically" broken - that's broken from an experience point of view. And I haven't re-installed the OS (this was an…

Yet it still swaps to disk ALL THE TIME and a new Terminal.app window can take up to 5 seconds to open. That's not swapping. That delay is /usr/bin/login searching the system logs so that it can display the date and time of your last login. Create a .hushlogin file in your home directory to prevent that.

It's painful guessing how many hours of my life I could have back if only I had known about this before. Thanks for the pain, thought_alarm.

Re: Something is deeply broken in OS X memory management

#82

Post by sciurus »

k-mcgrady wrote: post #62
gurkendoktor wrote: post #8

Earlier quoted context omitted.

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'm running on a 160GB HDD (nearly full), 2GB ram, on a 4 year old MacBook. I always have iTunes, Xcode, Safari/Chrome running with multiple tabs, and a mail client (Sparrow). The system originally ran Leopard and I upgraded to SL and then Lion. I wouldn't say it's slow. It's definitely getting slower but that's expected since it's such an old system. Could it be that you're just expecting too much from your computer…

"It's definitely getting slower but that's expected since it's such an old system."

I see this sentiment a lot, but I disagree with it. What are "iTunes, Xcode, Safari/Chrome, and a mail client" doing now that they weren't doing four years ago? Is it enough to justify their latest versions feeling less responsive than their versions from four years ago?

Re: Something is deeply broken in OS X memory management

#83

Post by collint »

follower wrote: post #13
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.

Can you explain a bit more how this works? The `purge` command has a pretty short man page: > purge -- force disk cache to be purged (flushed and emptied) > Purge can be used to approximate initial boot conditions with a cold disk buffer cache for performance analysis. It does not affect anonymous memory that has been allocated through malloc, vm_allocate, etc. [This seems to talk about it more: http://workstuff.tumb…

yeah, it's not directly attacking your 'inactive' memory. Just the disk cache, which shows up in the chart as 'inactive'. I'm not familiar with other cases that fit into the 'inactive' piece of the pie.

I have regularly seen 1-3G of ram get free'd up on a 'purge'

Re: Something is deeply broken in OS X memory management

#84

Post by sciurus »

spudlyo wrote: post #24
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 unfortun…

Isn't this what POSIX_FADV_DONTNEED is for?

http://linux.die.net/man/2/posix_fadvise

Re: Something is deeply broken in OS X memory management

#85

Post by jfb »

bo1024 wrote: post #79
jfb wrote: post #37

Earlier quoted context omitted.

Why shouldn't the kernel be using as much memory as possible? It's not like big disk caches or what have you cause your memory to go bad? As long as you get it back when you need it, who cares ?

The issue is just transparency. You want to know how much memory you actually have available for use if you need it. How would you like it if your car's gas gauge was close to empty all the time because the car was caching gas for long trips? It would seem there's a simple solution -- another number on the system monitor displaying how much memory is available for use if needed.

Flawed analogy: you use up the gas and your car stops. You use up memory and … the kernel swaps pages around. Now, if the kernel isn't giving you back memory, that's a problem, but the OP doesn't actually show that this is happening.

Re: Something is deeply broken in OS X memory management

#86

Post by dustingetz »

mistercow wrote: post #65
thought_alarm wrote: post #59

Earlier quoted context omitted.

Yet it still swaps to disk ALL THE TIME and a new Terminal.app window can take up to 5 seconds to open. That's not swapping. That delay is /usr/bin/login searching the system logs so that it can display the date and time of your last login. Create a .hushlogin file in your home directory to prevent that.

Wow, I'm really surprised this isn't default behavior. Knowing when you last logged in isn't nearly useful enough to justify the delay it so routinely causes.

It's worth it when you realize someone else has been logging on as you over the weekend.

Re: Something is deeply broken in OS X memory management

#87

Post by freehunter »

newobj wrote: post #68
gurkendoktor wrote: post #8

Earlier quoted context omitted.

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…

Insane amounts? Like 16G? That I can buy for like $80?

16GB is an insane amount, regardless of the price.

Re: Something is deeply broken in OS X memory management

#88

Post by ticks »

kirbysayshi wrote: post #66
colomon wrote: post #43

Earlier quoted context omitted.

For what it's worth, I'm running Snow Leopard (10.6.8) and I see the same sort of terrible performance the article describes. Though I did improve matters drastically by telling mds not to index my (Linux) MP3 server and my Time Machine drive. That made it go from nearly unusable to just frequently annoying. The other crazy thing I've been seeing is it routinely takes Chrome minutes to shutdown -- in fact, pretty muc…

Firefox 12 does this too, on both my MB Pro and iMac. I think it has to flush so many caches that disk I/O just takes forever. This is purely conjecture, though.

Not sure if it will help, but have you tried running Firefox's hidden profile manager and created a new profile? Firefox was horrible to run on OS X for me, it would drag the whole system down, but since changing to a new profile it has run like a dream and not reverted back.

Re: Something is deeply broken in OS X memory management

#89

Post by jonknee »

stephencanon wrote: post #42
jfb wrote: post #37

Earlier quoted context omitted.

Why shouldn't the kernel be using as much memory as possible? It's not like big disk caches or what have you cause your memory to go bad? As long as you get it back when you need it, who cares ?

This. Memory that is not used is wasted . If you spend a bunch of money on a high-memory setup, you should be furious if the OS doesn't use it all.

The problem is it then swaps to disk when you use an application. I'm fine with 100% memory being used at all times, but it needs to actually be used and preferably by whatever needs it the most.

Re: Something is deeply broken in OS X memory management

#90

Post by albertzeyer »

thought_alarm wrote: post #59
carguy1983 wrote: post #51

I have an 8-way Xeon Mac Pro w/ 20GB of RAM, almost half of which is 'free' at any point during the day unless I'm doing something really out of the ordinary. Yet it still swaps to disk ALL THE TIME and a new Terminal.app window can take up to 5 seconds to open. I really don't give a shit how it's not "technically" broken - that's broken from an experience point of view. And I haven't re-installed the OS (this was an…

Yet it still swaps to disk ALL THE TIME and a new Terminal.app window can take up to 5 seconds to open. That's not swapping. That delay is /usr/bin/login searching the system logs so that it can display the date and time of your last login. Create a .hushlogin file in your home directory to prevent that.

When the logs are read once, they should stay in the VFS cache as long as there is enough RAM, shouldn't they?

Anyway, instead of running /usr/bin/login, I just use /bin/zsh as my Terminal.app startup command which is much faster.

However, every time I access the file system, even some tab for autocompletion, it takes a few seconds. Even cd'ing into some directory can sometimes take a few seconds. Sometimes ~= it's more than 1h ago that I accessed that dir or so.

Edit: Maybe it's Time Machine or Spotlight or so which destroys the effectiveness of the VFS cache?

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