Re: [PATCH 07/11] unpaged: COW on VM_UNPAGED

From: Nick Piggin
Date: Fri Nov 18 2005 - 00:47:17 EST

David S. Miller wrote:
From: Hugh Dickins <hugh@xxxxxxxxxxx>
Date: Thu, 17 Nov 2005 19:37:23 +0000 (GMT)

Remove the BUG_ON(vma->vm_flags & VM_UNPAGED) from do_wp_page, and let
it do Copy-On-Write without touching the VM_UNPAGED's page counts - but
this is incomplete, because the anonymous page it inserts will itself
need to be handled, here and in other functions - next patch.

We still don't copy the page if the pfn is invalid, because the
copy_user_highpage interface does not allow it. But that's not been
a problem in the past: can be added in later if the need arises.

Signed-off-by: Hugh Dickins <hugh@xxxxxxxxxxx>

Do we even need this? It is a very serious question...

I think for 2.6.15, yes. We [read: I :(] was too hasty in removing
this completely. However I think it would not be unresonable to spit
out a warning, and remove it in 2.6.??

Looks like Hugh's done a very good job of this, however keeping
complexity down is always a good thing.

SUSE Labs, Novell Inc.

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