- Filtering special vmas.
- munlock()/munlockall() system call handling.
- Migrating mlocked pages.
+ - Compacting mlocked pages.
- mmap(MAP_LOCKED) system call handling.
- munmap()/exit()/exec() system call handling.
- try_to_unmap().
below, mlock_fixup() will attempt to merge the VMA with its neighbors or split
off a subset of the VMA if the range does not cover the entire VMA. Once the
VMA has been merged or split or neither, mlock_fixup() will call
-__mlock_vma_pages_range() to fault in the pages via get_user_pages() and to
+populate_vma_page_range() to fault in the pages via get_user_pages() and to
mark the pages as mlocked via mlock_vma_page().
Note that the VMA being mlocked might be mapped with PROT_NONE. In this case,
Also note that a page returned by get_user_pages() could be truncated or
migrated out from under us, while we're trying to mlock it. To detect this,
-__mlock_vma_pages_range() checks page_mapping() after acquiring the page lock.
+populate_vma_page_range() checks page_mapping() after acquiring the page lock.
If the page is still associated with its mapping, we'll go ahead and call
mlock_vma_page(). If the mapping is gone, we just unlock the page and move on.
In the worst case, this will result in a page mapped in a VM_LOCKED VMA
If the VMA is VM_LOCKED, mlock_fixup() again attempts to merge or split off the
specified range. The range is then munlocked via the function
-__mlock_vma_pages_range() - the same function used to mlock a VMA range -
+populate_vma_page_range() - the same function used to mlock a VMA range -
passing a flag to indicate that munlock() is being performed.
Because the VMA access protections could have been changed to PROT_NONE after
fetching the pages - all of which should be resident as a result of previous
mlocking.
-For munlock(), __mlock_vma_pages_range() unlocks individual pages by calling
+For munlock(), populate_vma_page_range() unlocks individual pages by calling
munlock_vma_page(). munlock_vma_page() unconditionally clears the PG_mlocked
flag using TestClearPageMlocked(). As with mlock_vma_page(),
munlock_vma_page() use the Test*PageMlocked() function to handle the case where
putback_lru_page() function to add migrated pages back to the LRU.
+COMPACTING MLOCKED PAGES
+------------------------
+
+The unevictable LRU can be scanned for compactable regions and the default
+behavior is to do so. /proc/sys/vm/compact_unevictable_allowed controls
+this behavior (see Documentation/sysctl/vm.txt). Once scanning of the
+unevictable LRU is enabled, the work of compaction is mostly handled by
+the page migration code and the same work flow as described in MIGRATING
+MLOCKED PAGES will apply.
+
+
mmap(MAP_LOCKED) SYSTEM CALL HANDLING
-------------------------------------
To mlock a range of memory under the unevictable/mlock infrastructure, the
mmap() handler and task address space expansion functions call
-mlock_vma_pages_range() specifying the vma and the address range to mlock.
-mlock_vma_pages_range() filters VMAs like mlock_fixup(), as described above in
-"Filtering Special VMAs". It will clear the VM_LOCKED flag, which will have
-already been set by the caller, in filtered VMAs. Thus these VMA's need not be
-visited for munlock when the region is unmapped.
-
-For "normal" VMAs, mlock_vma_pages_range() calls __mlock_vma_pages_range() to
-fault/allocate the pages and mlock them. Again, like mlock_fixup(),
-mlock_vma_pages_range() downgrades the mmap semaphore to read mode before
-attempting to fault/allocate and mlock the pages and "upgrades" the semaphore
-back to write mode before returning.
-
-The callers of mlock_vma_pages_range() will have already added the memory range
+populate_vma_page_range() specifying the vma and the address range to mlock.
+
+The callers of populate_vma_page_range() will have already added the memory range
to be mlocked to the task's "locked_vm". To account for filtered VMAs,
-mlock_vma_pages_range() returns the number of pages NOT mlocked. All of the
+populate_vma_page_range() returns the number of pages NOT mlocked. All of the
callers then subtract a non-negative return value from the task's locked_vm. A
negative return value represent an error - for example, from get_user_pages()
attempting to fault in a VMA with PROT_NONE access. In this case, we leave the
projects / firefly-linux-kernel-4.4.55.git / blobdiff