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| author | Kirill A. Shutemov <kirill.shutemov@linux.intel.com> | 2016-07-27 00:25:15 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-07-27 01:19:19 +0200 |
| commit | 6fb8ddfc455ca82a3ce674f54298cd20f27ca518 (patch) | |
| tree | e5bf5726da0e5e9d41ee7034969e7219be602fba /Documentation | |
| parent | khugepaged: recheck pmd after mmap_sem re-acquired (diff) | |
| download | linux-6fb8ddfc455ca82a3ce674f54298cd20f27ca518.tar.xz linux-6fb8ddfc455ca82a3ce674f54298cd20f27ca518.zip | |
thp, mlock: update unevictable-lru.txt
Add description of THP handling into unevictable-lru.txt.
Link: http://lkml.kernel.org/r/1466021202-61880-7-git-send-email-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/vm/unevictable-lru.txt | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/Documentation/vm/unevictable-lru.txt b/Documentation/vm/unevictable-lru.txt index fa3b527086fa..0026a8d33fc0 100644 --- a/Documentation/vm/unevictable-lru.txt +++ b/Documentation/vm/unevictable-lru.txt @@ -461,6 +461,27 @@ 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. +MLOCKING TRANSPARENT HUGE PAGES +------------------------------- + +A transparent huge page is represented by a single entry on an LRU list. +Therefore, we can only make unevictable an entire compound page, not +individual subpages. + +If a user tries to mlock() part of a huge page, we want the rest of the +page to be reclaimable. + +We cannot just split the page on partial mlock() as split_huge_page() can +fail and new intermittent failure mode for the syscall is undesirable. + +We handle this by keeping PTE-mapped huge pages on normal LRU lists: the +PMD on border of VM_LOCKED VMA will be split into PTE table. + +This way the huge page is accessible for vmscan. Under memory pressure the +page will be split, subpages which belong to VM_LOCKED VMAs will be moved +to unevictable LRU and the rest can be reclaimed. + +See also comment in follow_trans_huge_pmd(). mmap(MAP_LOCKED) SYSTEM CALL HANDLING ------------------------------------- |