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author | Linus Torvalds <torvalds@linux-foundation.org> | 2009-01-30 11:37:22 -0800 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-01-30 11:37:22 -0800 |
commit | 33bfad54b58cf05cfe6678c3ec9235d4bc8db4c2 (patch) | |
tree | d6be0ff97effa23289b2566acf8e56a49aa5657e | |
parent | c01a25e7cf6dcb0fa69c155706d5dd1e76e53796 (diff) | |
download | op-kernel-dev-33bfad54b58cf05cfe6678c3ec9235d4bc8db4c2.zip op-kernel-dev-33bfad54b58cf05cfe6678c3ec9235d4bc8db4c2.tar.gz |
Allow opportunistic merging of VM_CAN_NONLINEAR areas
Commit de33c8db5910cda599899dd431cc30d7c1018cbf ("Fix OOPS in
mmap_region() when merging adjacent VM_LOCKED file segments") unified
the vma merging of anonymous and file maps to just one place, which
simplified the code and fixed a use-after-free bug that could cause an
oops.
But by doing the merge opportunistically before even having called
->mmap() on the file method, it now compares two different 'vm_flags'
values: the pre-mmap() value of the new not-yet-formed vma, and previous
mappings of the same file around it.
And in doing so, it refused to merge the common file case, which adds a
marker to say "I can be made non-linear".
This fixes it by just adding a set of flags that don't have to match,
because we know they are ok to merge. Currently it's only that single
VM_CAN_NONLINEAR flag, but at least conceptually there could be others
in the future.
Reported-and-acked-by: Hugh Dickins <hugh@veritas.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Greg KH <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | mm/mmap.c | 5 |
1 files changed, 4 insertions, 1 deletions
@@ -658,6 +658,9 @@ again: remove_next = 1 + (end > next->vm_end); 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. @@ -665,7 +668,7 @@ again: remove_next = 1 + (end > next->vm_end); static inline int is_mergeable_vma(struct vm_area_struct *vma, struct file *file, unsigned long vm_flags) { - if (vma->vm_flags != vm_flags) + if ((vma->vm_flags ^ vm_flags) & ~VM_MERGEABLE_FLAGS) return 0; if (vma->vm_file != file) return 0; |