memcpy error


 
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# 22  
Old 10-22-2011
Hmm, I wonder what happens if you try to read a few GB from a SAN-based file system built on 4 or 6 or maybe more parallel LUNs configured by someone who knows how to lay out storage, and attached with 8 gbps fiber?

Do you really think the VM manager in your kernel can keep up with data coming in that fast?

Guess what? It can't.

Heck, I've seen well-designed 2 gbps SANs with just a few LUNs overwhelm VM managers.

In other words, YES, there ARE reasons to memset() a chunk of RAM *before* you use it.

And that's not even addressing the default Linux method of allowing oversubscription of virtual mamory in the hope that it won't all be used. If reliability and deterministic behavoir are important to you, you don't rely on hope and things like the Linux OOM killer are crazy-bad.
# 23  
Old 10-24-2011
Quote:
Originally Posted by achenle
And that's not even addressing the default Linux method of allowing oversubscription of virtual mamory in the hope that it won't all be used. If reliability and deterministic behavoir are important to you, you don't rely on hope and things like the Linux OOM killer are crazy-bad.
Other UNIX have OOM-killers as well.

Lest you complain that's configurable, that's configurable on Linux as well.

The way to gracefully avoid zero-memory situations is the same on every UNIX -- "don't let it happen". That's what program limits and other such schemes are for.

Last edited by Corona688; 10-24-2011 at 01:09 PM..
# 24  
Old 10-24-2011
Quote:
Originally Posted by achenle
Hmm, I wonder what happens if you try to read a few GB from a SAN-based file system built on 4 or 6 or maybe more parallel LUNs configured by someone who knows how to lay out storage, and attached with 8 gbps fiber?

Do you really think the VM manager in your kernel can keep up with data coming in that fast?

Guess what? It can't.

Heck, I've seen well-designed 2 gbps SANs with just a few LUNs overwhelm VM managers.

In other words, YES, there ARE reasons to memset() a chunk of RAM *before* you use it.

And that's not even addressing the default Linux method of allowing oversubscription of virtual mamory in the hope that it won't all be used. If reliability and deterministic behavoir are important to you, you don't rely on hope and things like the Linux OOM killer are crazy-bad.
I'm not sure what you're getting at here.... Are you saying the reason to call memset is to assist the VMM in keeping up with a fast transfer?
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