diff options
| -rw-r--r-- | Documentation/vm/unevictable-lru.txt | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/Documentation/vm/unevictable-lru.txt b/Documentation/vm/unevictable-lru.txt index 3be0bfc4738d..32ee3a67dba2 100644 --- a/Documentation/vm/unevictable-lru.txt +++ b/Documentation/vm/unevictable-lru.txt @@ -467,7 +467,13 @@ mmap(MAP_LOCKED) SYSTEM CALL HANDLING In addition the mlock()/mlockall() system calls, an application can request that a region of memory be mlocked supplying the MAP_LOCKED flag to the mmap() -call. Furthermore, any mmap() call or brk() call that expands the heap by a +call. There is one important and subtle difference here, though. mmap() + mlock() +will fail if the range cannot be faulted in (e.g. because mm_populate fails) +and returns with ENOMEM while mmap(MAP_LOCKED) will not fail. The mmaped +area will still have properties of the locked area - aka. pages will not get +swapped out - but major page faults to fault memory in might still happen. + +Furthermore, any mmap() call or brk() call that expands the heap by a task that has previously called mlockall() with the MCL_FUTURE flag will result in the newly mapped memory being mlocked. Before the unevictable/mlock changes, the kernel simply called make_pages_present() to allocate pages and |