Re: why VM_SHM has been removed from mm.h?

[Hugh Dickins <hugh@veritas.com>]

On Tue, 28 Feb 2006, Kamran Karimi wrote:
> 
> VM_SHM is used by DIPC to quickly recognise when we are dealing with a System
> V IPC segment. It has been "removed" from recent kernels (set to 0).

Curious: VM_SHM wasn't set on a System V IPC shm vma in any 2.4 or 2.6
kernel that I know of; but was set on the vmas of a random collection
of drivers.  Perhaps you've been using your own patch to set it on
SysV IPC shm vmas, and clear it from drivers' vmas?

(We'll remove VM_SHM entirely once I've trawled through those drivers.)

> Is there an easy way to find out if a segment is a Sys V shm?

Nothing easy and reliable springs immediately to mind - from a VM point
of view, they're treated much the same as tmpfs files; but there
probably is some hacky way if we think about it long enough.

> if not, I suggest we re-activate it.

It seems that either you've been doing the wrong thing up to now,
and never noticed it; or that you've been using your own flag in
your own patch, and can continue to do so.  No need for vanilla
kernel to reinstate VM_SHM.

Are you sure you need to recognize them?

Hugh
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