mm: Fix typo in unevictable-lru.txt

     process because mlocked pages are migratable.  However, for reclaim, if

     the page is mapped into a VM_LOCKED VMA, the scan stops.

     try_to_unmap_anon() attempts to acquire in read mode the mmap semphore of

     try_to_unmap_anon() attempts to acquire in read mode the mmap semaphore of

     the mm_struct to which the VMA belongs.  If this is successful, it will

     mlock the page via mlock_vma_page() - we wouldn't have gotten to

     try_to_unmap_anon() if the page were already mlocked - and will return

processing.  Again, these functions walk the respective reverse maps looking

for VM_LOCKED VMAs.  When such a VMA is found for anonymous pages and file

pages mapped in linear VMAs, as in the try_to_unmap() case, the functions

attempt to acquire the associated mmap semphore, mlock the page via

attempt to acquire the associated mmap semaphore, mlock the page via

mlock_vma_page() and return SWAP_MLOCK.  This effectively undoes the

pre-clearing of the page's PG_mlocked done by munlock_vma_page.

Note that try_to_munlock()'s reverse map walk must visit every VMA in a page's

reverse map to determine that a page is NOT mapped into any VM_LOCKED VMA.

However, the scan can terminate when it encounters a VM_LOCKED VMA and can

successfully acquire the VMA's mmap semphore for read and mlock the page.

successfully acquire the VMA's mmap semaphore for read and mlock the page.

Although try_to_munlock() might be called a great many times when munlocking a

large region or tearing down a large address space that has been mlocked via

mlockall(), overall this is a fairly rare event.