On Tue, 21 Mar 2000 09:04:04 -0800 (PST), you wrote:
>
>[CC list trimmed again, I doubt Stephen Tweedie or Rik van Riel are
>interested in this discussion.]
>
>On Tue, 21 Mar 2000, James Sutherland wrote:
>
>>>Preventing system OOM using resource limits is equivalent to disabling
>>>overcommit. You have to restrict each of N users to 1/N of the total
>>>system memory.
>>
>>No. That is NOT overcommit. Overcommit, in this context, is when a
>>process calls malloc() and is given unpopulated address space, which
>>will be populated on use.
>
>In the quota case, in order to prevent a system-wide OOM you must give
>each of N users an average of 1/N of the total system memory (ignoring
>kernel overhead). The side effect is that overcommittment is now
>impossible, because the system can only be overcommitted if a user has
>exceeded their quota, which is not allowed...
>
>Unless you don't count COW pages against a user's quota?
No; overcommit involves something totally different. All the users
could have malloc()ed 2Gb blocks of address space, provided they
didn't USE it. (A sparse matrix, for example. A classic example of
overcommit making code MUCH simpler.)
Overcommit doesn't involve quotas. It just involves demand-allocation
of memory.
James.
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