[Openmcl-devel] Decreasing the size of the reserved heap

Tim Bradshaw tfb at tfeb.org
Fri Jan 10 04:56:52 PST 2014

On 9 Jan 2014, at 18:44, R. Matthew Emerson wrote:

> Sorry if I'm restating an obvious point, but when CCL wants to use some of the address space that it mapped with MAP_NORESERVE, it changes that portion of the mapping (thereby causing actual VM consumption), and can signal an out-of-memory error if that remapping fails.

Yes that's fine: I'm very happy with applications being able to say they don't want to reserve swap because they can deal with the implications, what is bad is not being able to say that they *do* want to reserve swap, and especially if reserving swap is not the default thing to do, since it means that naive applications (or their users) will get unpleasant surprises.

(The reason I care about all this is that in my day job I deal with big expensive databases which often turn out to be naive applications in this sense (or did, I think they may have learnt now) which, combined with the Linux overcommit behaviour (which again is better now) and a let's-just-put-everything-on-linux-and-ignore-that-weird-guy-whining-about-overcommit strategy led to some quite serious headless-chickening.  And I resent that I never got credit for the whining, as well.)


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