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Re: AMAP_SHARED (was Re: XIP)
> A few more comments:
> - AMAP_SHARED itself is a fine concept; it's used by shared memory.
> 452 error = uvm_map(&vm->vm_map, &attach_va, size, uobj, 0,
> 453 UVM_MAPFLAG(prot, prot, UVM_INH_SHARE,
> UVM_ADV_RANDOM, flags));
> (Note UVM_INH_SHARE == MAP_INHERIT_SHARE).
sysv shm is backed by an aobj and does not involve amap.
iirc, you need minherit to create shared-cow mappings.
(imo, the introduction of minherit was a mistake because it
merely complicated vm.)
> I guess MAP_INHERIT_SHARE was added because adding it was easy
> after shared amap was implemented for shared memory?
> - For highly tuned, XIP'ed systems, programs should be designed to
> avoid .data, because they're COW'ed to page cache sooner or later.
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