From 471eab186865eefb189ac9c549a17b283ff5af57 Mon Sep 17 00:00:00 2001 From: ken Date: Sat, 8 Mar 2003 06:58:18 +0000 Subject: Zero copy send and receive fixes: - On receive, vm_map_lookup() needs to trigger the creation of a shadow object. To make that happen, call vm_map_lookup() with PROT_WRITE instead of PROT_READ in vm_pgmoveco(). - On send, a shadow object will be created by the vm_map_lookup() in vm_fault(), but vm_page_cowfault() will delete the original page from the backing object rather than simply letting the legacy COW mechanism take over. In other words, the new page should be added to the shadow object rather than replacing the old page in the backing object. (i.e. vm_page_cowfault() should not be called in this case.) We accomplish this by making sure fs.object == fs.first_object before calling vm_page_cowfault() in vm_fault(). Submitted by: gallatin, alc Tested by: ken --- sys/vm/vm_fault.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) (limited to 'sys/vm') diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c index e443a00..a620576 100644 --- a/sys/vm/vm_fault.c +++ b/sys/vm/vm_fault.c @@ -310,11 +310,18 @@ RetryFault:; int queue, s; /* - * check for page-based copy on write + * check for page-based copy on write. + * We check fs.object == fs.first_object so + * as to ensure the legacy COW mechanism is + * used when the page in question is part of + * a shadow object. Otherwise, vm_page_cowfault() + * removes the page from the backing object, + * which is not what we want. */ vm_page_lock_queues(); if ((fs.m->cow) && - (fault_type & VM_PROT_WRITE)) { + (fault_type & VM_PROT_WRITE) && + (fs.object == fs.first_object)) { s = splvm(); vm_page_cowfault(fs.m); splx(s); -- cgit v1.1