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Subject[PATCH 12/12] ksm: remove VM_MERGEABLE_FLAGS
KSM originally stood for Kernel Shared Memory: but the kernel has long
supported shared memory, and VM_SHARED and VM_MAYSHARE vmas, and KSM is
something else. So we switched to saying "merge" instead of "share".

But Chris Wright points out that this is confusing where mmap.c merges
adjacent vmas: most especially in the name VM_MERGEABLE_FLAGS, used by
is_mergeable_vma() to let vmas be merged despite flags being different.

Call it VMA_MERGE_DESPITE_FLAGS? Perhaps, but at present it consists
only of VM_CAN_NONLINEAR: so for now it's clearer on all sides to use
that directly, with a comment on it in is_mergeable_vma().

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
---
This patch got lost along the way last time: no big deal but try again.
mm/mmap.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
--- ksm11/mm/mmap.c 2009-08-02 13:50:41.000000000 +0100
+++ ksm12/mm/mmap.c 2009-08-02 13:51:04.000000000 +0100
@@ -660,9 +660,6 @@ again: remove_next = 1 + (end > next->
validate_mm(mm);
}

-/* Flags that can be inherited from an existing mapping when merging */
-#define VM_MERGEABLE_FLAGS (VM_CAN_NONLINEAR)
-
/*
* If the vma has a ->close operation then the driver probably needs to release
* per-vma resources, so we don't attempt to merge those.
@@ -670,7 +667,8 @@ again: remove_next = 1 + (end > next->
static inline int is_mergeable_vma(struct vm_area_struct *vma,
struct file *file, unsigned long vm_flags)
{
- if ((vma->vm_flags ^ vm_flags) & ~VM_MERGEABLE_FLAGS)
+ /* VM_CAN_NONLINEAR may get set later by f_op->mmap() */
+ if ((vma->vm_flags ^ vm_flags) & ~VM_CAN_NONLINEAR)
return 0;
if (vma->vm_file != file)
return 0;

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