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Linux Memory Management FAQ

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Re: Linux Memory Management FAQ

#71

Post by ymbeld »

ben_bai wrote: post #67
ymbeld wrote: post #49

Earlier quoted context omitted.

I don’t know what true OOM means, but my desktop has crashed I think at least three times in the last four months and the console said “OOM killer”. About 15GB of usable RAM, 2GB swap drive. I just have to have the usual applications open plus another browser in addition to Firefox, namely Chrome. (But naturally I don’t try to actively reproduce the behavior since I usually have better things to do than wait 10 minut…

Your problem is the 2GB of swap. Get rid of it and it will just crash without 10min of slowdown (while swap disk is getting written to). Linux overcommitting memory and especially chrome/firefox beeing big-fat-memory-hogs are the problem. In fact every application which doesn't cope malloc beeing out of memory or assuming everybody has multiple gigs of memory to spare should "reevaluate".

Seriously though that’s a good idea. Might be better to just disable swap. :) Well, at least until I go out and buy more RAM.

Re: Linux Memory Management FAQ

#72

Post by saagarjha »

haberman wrote: post #46
xxpor wrote: post #23

Earlier quoted context omitted.

This is true for x86-64, not true for other architectures such as arm64. Apple uses the high bits to cryptographicly sign the pointer value.

Hmm, it appears that the top byte on arm64 is only ignored if TBI (Top Byte Ignore) is enabled. I don't think pointer signing requires TBI though. Pointer signing uses the PAC instruction to sign a pointer, and the AUT instruction to verify and unpack the signed pointer, but in its signed/packed form it is not a usable pointer. So actual addressable pointers need not support non-canonical addresses.

Apple runs PAC without TBI enabled, I believe.

Re: Linux Memory Management FAQ

#73

Post by saagarjha »

danielheath wrote: post #35
everybodyknows wrote: post #28

Earlier quoted context omitted.

Fascinating. Does this confer some of the benefits of ECC RAM, for pointer data only — without the hardware cost?

Some (but I believe the advantage is that it’s much harder to inject valid code from a buffer overflow).

PAC is more about CFI than preventing shellcode injection (which is done through codesigning and memory protection, mostly).

Re: Linux Memory Management FAQ

#74

Post by ben_bai »

ymbeld wrote: post #71
ben_bai wrote: post #67

Earlier quoted context omitted.

Your problem is the 2GB of swap. Get rid of it and it will just crash without 10min of slowdown (while swap disk is getting written to). Linux overcommitting memory and especially chrome/firefox beeing big-fat-memory-hogs are the problem. In fact every application which doesn't cope malloc beeing out of memory or assuming everybody has multiple gigs of memory to spare should "reevaluate".

Seriously though that’s a good idea. Might be better to just disable swap. :) Well, at least until I go out and buy more RAM.

The soft way would be to set ulimit for memory to something other than unlimited. To cap the max mem limit per process

Re: Linux Memory Management FAQ

#75

Post by ymbeld »

ben_bai wrote: post #74
ymbeld wrote: post #71

Earlier quoted context omitted.

Seriously though that’s a good idea. Might be better to just disable swap. :) Well, at least until I go out and buy more RAM.

The soft way would be to set ulimit for memory to something other than unlimited. To cap the max mem limit per process

Thanks, that’s a good suggestion.
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