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List:       linux-kernel
Subject:    Re: can't mlockall() more than 128MB, is this a kernel limitiation ?
From:       Benno Senoner <sbenno () gardena ! net>
Date:       2000-08-05 15:57:10
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On Sat, 05 Aug 2000, Benno Senoner wrote:

hmmm .. I looked at the source and seems that I can answer this question by
myself:

> 
> Now my question: is this more than 128MB mlock() problem a limitation of the
> 2.2.x kernel or can it be lifted by some sysctl ?

Yes, see   mm/mlock.c
-----
        /* we may lock at most half of physical memory... */
        /* (this check is pretty bogus, but doesn't hurt) */
        if (locked > num_physpages/2)
                goto out;
-----

Argh ! this is bogus ! , on my 250MB RAM BOX , I want to be able to mlock at
least something like 200-220MB ,

What is the purpose of this artificial limitation ?
I agree that running out of phys pages is bad, but with those big mem sizes like
256-512MB, a margin of 30-50MB (configurable) should be enough.

Can we make this configurable via sysctl in 2.4 ?
(without this realtime multimedia apps will be unable to take advantage of the
full amount of RAM, because swappable mem is useless in certain cases)

> 
> Does kernel 2.4 have the same limitiation ? 

Yes  :-(

same code present in 2.4-test6-pre2.

But I was really wondering : am I the only one that needs more than
ramsize/2  mlocked() mem in a single process ?
hopefully not ...

let me know

thanks,
Benno.



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