On Tue, 10 Jul 2007, Dave McCracken wrote:
> On Tuesday 10 July 2007, Hugh Dickins wrote:
> > > >
> > > > This brings the Linux behavior in line with what is documented in the
> > > > POSIX man page for setrlimit(3p).
> >
> > Which says malloc() can fail from it, but conspicuously not that mmap()
> > can fail from it: unlike the RLIMIT_AS case. Would we be better off?
>
> True. But keep in mind that when POSIX was written mmap() was new and shiny
> and pretty much only used for shared mappings, and definitely not used by
> malloc().
Well, my bookmark is to SUSv3, which I think is equivalent these days?
And that specifically says malloc() or mmap() in the RLIMIT_AS case,
but only malloc() in the RLIMIT_DATA case. We're wrong either way.
> Given that RLIMIT_DATA is pretty much meaningless in current kernels, I would
> put forward the argument that this change is extremely unlikely to break
> anything because no one is currently setting it to anything other than
> unlimited. Adding this feature would give administrators another tool, a way
> to control the private data size of a process without restricting its ability
> to attach to large shared mappings.
That may be a good argument (though "extremely unlikely to break"s
have a nasty habit of biting). I'd still say that the contribution
to Committed_AS is more appropriate and more useful here.
> > That change to /proc/PID/status VmData:
> > - data = mm->total_vm - mm->shared_vm - mm->stack_vm;
> > + data = mm->total_vm - mm->shared_vm - mm->stack_vm - mm->exec_vm;
> > looks plausible, but isn't exec_vm already counted as shared_vm,
> > so now being doubly subtracted? Besides which, we wouldn't want
> > to change those numbers again without consulting Albert.
>
> As I recall, this was added after Herbert discovered that exec_vm is not
> counted as shared_vm. It's actually mapped as private/readonly.
Mapped private readonly yes, but vm_stat_account() says
if (file) {
mm->shared_vm += pages;
if ((flags & (VM_EXEC|VM_WRITE)) == VM_EXEC)
mm->exec_vm += pages;
Hugh
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