On Tue, Mar 15, 2016 at 08:30:54AM -0700, Dave Hansen wrote: > On 03/15/2016 07:55 AM, Kirill A. Shutemov wrote: > > +Transparent huge page is represented by single entry on a lru list and > > +therefore we can only make unevictable entire compound page, not > > +individual subpages. > > A few grammar nits: > > 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. Thanks. > > +We handle this by forbidding mlocking PTE-mapped huge pages. This way we > > +keep the huge page accessible for vmscan. Under memory pressure the page > > +will be split, subpages from VM_LOCKED VMAs moved to unevictable lru and > > +the rest can be evicted. > > What do you mean by "mlocking" in this context? Do you mean that we > actually return -ESOMETHING from mlock() on PTE-mapped huge pages? Or, > do you just mean that we defer treating PTE-mapped huge pages as > PageUnevictable() inside the kernel? The latter. > I think we should probably avoid saying "mlocking" when we really mean > "kernel-internal mlocked page handling" aka. the unevictable list. What about "We handle this by keeping PTE-mapped huge pages on normal LRU lists." ? The updated patch is below. >From 9d9ba3b5a65cd152d70bd1e3a4866dd0564a737f Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Date: Tue, 15 Mar 2016 17:48:16 +0300 Subject: [PATCH] thp, mlock: update unevictable-lru.txt Add description of THP handling into unevictable-lru.txt. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> --- Documentation/vm/unevictable-lru.txt | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/Documentation/vm/unevictable-lru.txt b/Documentation/vm/unevictable-lru.txt index fa3b527086fa..c47566fc49cb 100644 --- a/Documentation/vm/unevictable-lru.txt +++ b/Documentation/vm/unevictable-lru.txt @@ -461,6 +461,25 @@ 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 +------------------------------- + +Transparent huge page is represented by single entry on a lru list and +therefore we can only make unevictable entire compound page, not +individual subpages. + +We allow a part of transparent huge page to be mapped PTEs (i.e. after +mremap() or mprotect()) and VMA with PTE-mapped huge page can be mlocked. + +That means we need to be careful, not making entire huge page unevicable +if user mlock() only part of it. + +We handle this by forbidding mlocking PTE-mapped huge pages. This way we +keep the huge page accessible for vmscan. Under memory pressure the page +will be split, subpages from VM_LOCKED VMAs moved to unevictable lru and +the rest can be evicted. + +See also comment in follow_trans_huge_pmd(). mmap(MAP_LOCKED) SYSTEM CALL HANDLING ------------------------------------- -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>