Messages in this thread | | | Date | Mon, 6 Mar 2000 15:32:33 -0500 (EST) | From | Gregory Maxwell <> | Subject | Re: Linux 2.2.15pre12 |
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Very correct. Sorry. :)
On Mon, 6 Mar 2000, Paul Jakma wrote:
> On Mon, 6 Mar 2000, Gregory Maxwell wrote: > > Yes, you can currently do this. Turning off overcommit doesn't stop COW, > but it takes away it's memory/swap advantage. > > [snip] > > as i understand you can't turn off overcommit in linux at the > > moment. Yet it would be a useful option to have. I can easily imagine > > certain situations where i would choose to turn off overcommit at the > > expense of more swap if it would guarantee that OOM would never > > happen. (hard disk space is cheap compared to downtime) > [snip] > > /proc/sys/vm/overcommit_memory > overcommit_memory: > > This value contains a flag that enables memory overcommitment. > When this flag is 0, the kernel checks before each malloc() > to see if there's enough memory left. If the flag is nonzero, > the system pretends there's always enough memory. > > This feature can be very useful because there are a lot of > programs that malloc() huge amounts of memory "just-in-case" > and don't much of it. > > i think you're misunderstanding the overcommit_memory sysctl. From > the wording above, the default of 0 gives us the normal (relaxed) > linux VM allocation policy. Setting it to > 0 *turns off* this > checking even altogether!!! > > Look at: mm/mmap.c::vm_enough_memory() for more information. > > > => > > /* Sometimes we want to use more memory than we have. */ > if (sysctl_overcommit_memory) > return 1; > > ie if overcommit_memory != 0 then we throw the already sparse > accounting checks out of the window. It does not turn off > overcommit!! It makes linux VM even more relaxed!!! > > regards, > -- > Paul Jakma paul@clubi.ie > PGP5 key: http://www.clubi.ie/jakma/publickey.txt > ------------------------------------------- > Fortune: > I am a friend of the working man, and I would rather be his friend > than be one. > -- Clarence Darrow > >
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