Re: Memory overcommit

From: Vedran FuraÄ
Date: Mon Nov 02 2009 - 14:56:33 EST

Andrea Arcangeli wrote:

> On Fri, Oct 30, 2009 at 03:41:12PM +0100, Vedran FuraÄ wrote:
>> Oh... so this is because apps "reserve" (Committed_AS?) more then they
>> currently need.
> They don't actually reserve, they end up "reserving" if overcommit is
> set to 2 (OVERCOMMIT_NEVER)... Apps aren't reserving, more likely they
> simply avoid a flood of mmap when a single one is enough to map an
> huge MAP_PRIVATE region like shared libs that you may only execute
> partially (this is why total_vm is usually much bigger than real ram
> mapped by pagetables represented in rss). But those shared libs are
> 99% pageable and they don't need to stay in swap or ram, so
> overcommit-as greatly overstimates the actual needs even if shared lib
> loading wouldn't be 64bit optimized (i.e. large and a single one).

Thanks for info!

>> 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.
> Add more swap.

I don't use swap. With current prices of RAM, swap is history, at least
for desktops. I hate when e.g. firefox gets swapped out if I don't use
it for a while. Removing swap decreased desktop latencies drastically.
And I don't care much if I'll loose 100MB of potential free memory that
could be used for disk cache...



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