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authorLinus Torvalds <torvalds@g5.osdl.org>2005-12-12 06:46:02 +0300
committerLinus Torvalds <torvalds@g5.osdl.org>2005-12-12 06:46:02 +0300
commitfb155c1619f056ae9765eed272cd6aba6e1a7399 (patch)
tree04a82b5fbf83bdb9dcf7fec9aeaaecf92532d88c
parente4f5c82a92c2a546a16af1614114eec19120e40a (diff)
downloadlinux-fb155c1619f056ae9765eed272cd6aba6e1a7399.tar.xz
Allow arbitrary shared PFNMAP's
A shared mapping doesn't cause COW-pages, so we don't need to worry about the whole vm_pgoff logic to decide if a PFN-remapped page has gone through COW or not. This makes it possible to entirely avoid the special "partial remapping" logic for the common case. Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--mm/memory.c16
1 files changed, 12 insertions, 4 deletions
diff --git a/mm/memory.c b/mm/memory.c
index aa8af0e20269..e65f8fc8ea67 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -377,6 +377,8 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, pte_
unsigned long off = (addr - vma->vm_start) >> PAGE_SHIFT;
if (pfn == vma->vm_pgoff + off)
return NULL;
+ if (vma->vm_flags & VM_SHARED)
+ return NULL;
}
/*
@@ -1343,9 +1345,6 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
struct mm_struct *mm = vma->vm_mm;
int err;
- if (addr != vma->vm_start || end != vma->vm_end)
- return incomplete_pfn_remap(vma, addr, end, pfn, prot);
-
/*
* Physically remapped pages are special. Tell the
* rest of the world about it:
@@ -1359,9 +1358,18 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
* VM_PFNMAP tells the core MM that the base pages are just
* raw PFN mappings, and do not have a "struct page" associated
* with them.
+ *
+ * There's a horrible special case to handle copy-on-write
+ * behaviour that some programs depend on. We mark the "original"
+ * un-COW'ed pages by matching them up with "vma->vm_pgoff".
*/
+ if (!(vma->vm_flags & VM_SHARED)) {
+ if (addr != vma->vm_start || end != vma->vm_end)
+ return incomplete_pfn_remap(vma, addr, end, pfn, prot);
+ vma->vm_pgoff = pfn;
+ }
+
vma->vm_flags |= VM_IO | VM_RESERVED | VM_PFNMAP;
- vma->vm_pgoff = pfn;
BUG_ON(addr >= end);
pfn -= addr >> PAGE_SHIFT;