Re: Memory overcommit

[Vedran FuraÄ]

Andrea Arcangeli wrote:

> On Fri, Oct 30, 2009 at 02:53:33PM +0100, Vedran FuraÄ wrote:
>> % free -m
>>           total       used       free     shared    buffers     cached
>> Mem:      3458        3429         29          0        102       1119
>> -/+ buffers/cache:    2207       1251
>>
>> There's plenty of memory available. Shouldn't cache be automatically
>> dropped (this question was in my original mail, hence the subject)?
> 
> This is not about cache, cache amount is physical, this about
> virtual amount that can only go in ram or swap (at any later time,
> current time is irrelevant) vs "ram + swap".

Oh... so this is because apps "reserve" (Committed_AS?) more then they
currently need.

> In short add more swap if
> you don't like overcommit and check grep Commit /proc/meminfo in case
> this is accounting bug...

A the time of "malloc: Cannot allocate memory":

CommitLimit:     3364440 kB
Committed_AS:    3240200 kB

So probably everything is ok (and free is misleading). Overcommit is
unfortunately necessary if I want to be able to use all my memory.

Btw. http://www.redhat.com/advice/tips/meminfo.html says Committed_AS is
a (gu)estimate. Hope it is a good (not to high) guesstimate. :)

Regards,

Vedran

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