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authorDave Airlie <airlied@redhat.com>2015-04-20 01:32:26 (GMT)
committerDave Airlie <airlied@redhat.com>2015-04-20 03:05:20 (GMT)
commit2c33ce009ca2389dbf0535d0672214d09738e35e (patch)
tree6186a6458c3c160385d794a23eaf07c786a9e61b /Documentation/vm/unevictable-lru.txt
parentcec32a47010647e8b0603726ebb75b990a4057a4 (diff)
parent09d51602cf84a1264946711dd4ea0dddbac599a1 (diff)
downloadlinux-2c33ce009ca2389dbf0535d0672214d09738e35e.tar.xz
Merge Linus master into drm-next
The merge is clean, but the arm build fails afterwards, due to API changes in the regulator tree. I've included the patch into the merge to fix the build. Signed-off-by: Dave Airlie <airlied@redhat.com>
Diffstat (limited to 'Documentation/vm/unevictable-lru.txt')
-rw-r--r--Documentation/vm/unevictable-lru.txt38
1 files changed, 20 insertions, 18 deletions
diff --git a/Documentation/vm/unevictable-lru.txt b/Documentation/vm/unevictable-lru.txt
index 744f82f..3be0bfc 100644
--- a/Documentation/vm/unevictable-lru.txt
+++ b/Documentation/vm/unevictable-lru.txt
@@ -22,6 +22,7 @@ CONTENTS
- 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().
@@ -317,7 +318,7 @@ If the VMA passes some filtering as described in "Filtering Special Vmas"
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,
@@ -327,7 +328,7 @@ fault path or in vmscan.
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
@@ -392,7 +393,7 @@ ignored for munlock.
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
@@ -402,7 +403,7 @@ get_user_pages() was enhanced to accept a flag to ignore the permissions when
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
@@ -450,6 +451,17 @@ list because of a race between munlock and migration, page migration uses the
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
-------------------------------------
@@ -463,21 +475,11 @@ populate the page table.
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