From 2916ecc0f9d435d849c98f4da50e453124c87531 Mon Sep 17 00:00:00 2001 From: Jérôme Glisse Date: Fri, 8 Sep 2017 16:12:06 -0700 Subject: mm/migrate: new migrate mode MIGRATE_SYNC_NO_COPY MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Introduce a new migration mode that allow to offload the copy to a device DMA engine. This changes the workflow of migration and not all address_space migratepage callback can support this. This is intended to be use by migrate_vma() which itself is use for thing like HMM (see include/linux/hmm.h). No additional per-filesystem migratepage testing is needed. I disables MIGRATE_SYNC_NO_COPY in all problematic migratepage() callback and i added comment in those to explain why (part of this patch). The commit message is unclear it should say that any callback that wish to support this new mode need to be aware of the difference in the migration flow from other mode. Some of these callbacks do extra locking while copying (aio, zsmalloc, balloon, ...) and for DMA to be effective you want to copy multiple pages in one DMA operations. But in the problematic case you can not easily hold the extra lock accross multiple call to this callback. Usual flow is: For each page { 1 - lock page 2 - call migratepage() callback 3 - (extra locking in some migratepage() callback) 4 - migrate page state (freeze refcount, update page cache, buffer head, ...) 5 - copy page 6 - (unlock any extra lock of migratepage() callback) 7 - return from migratepage() callback 8 - unlock page } The new mode MIGRATE_SYNC_NO_COPY: 1 - lock multiple pages For each page { 2 - call migratepage() callback 3 - abort in all problematic migratepage() callback 4 - migrate page state (freeze refcount, update page cache, buffer head, ...) } // finished all calls to migratepage() callback 5 - DMA copy multiple pages 6 - unlock all the pages To support MIGRATE_SYNC_NO_COPY in the problematic case we would need a new callback migratepages() (for instance) that deals with multiple pages in one transaction. Because the problematic cases are not important for current usage I did not wanted to complexify this patchset even more for no good reason. Link: http://lkml.kernel.org/r/20170817000548.32038-14-jglisse@redhat.com Signed-off-by: Jérôme Glisse Cc: Aneesh Kumar Cc: Balbir Singh Cc: Benjamin Herrenschmidt Cc: Dan Williams Cc: David Nellans Cc: Evgeny Baskakov Cc: Johannes Weiner Cc: John Hubbard Cc: Kirill A. Shutemov Cc: Mark Hairgrove Cc: Michal Hocko Cc: Paul E. McKenney Cc: Ross Zwisler Cc: Sherry Cheung Cc: Subhash Gutti Cc: Vladimir Davydov Cc: Bob Liu Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/ubifs/file.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'fs/ubifs') diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c index f90a466ea5db..a02aa59d1e24 100644 --- a/fs/ubifs/file.c +++ b/fs/ubifs/file.c @@ -1490,7 +1490,10 @@ static int ubifs_migrate_page(struct address_space *mapping, SetPagePrivate(newpage); } - migrate_page_copy(newpage, page); + if (mode != MIGRATE_SYNC_NO_COPY) + migrate_page_copy(newpage, page); + else + migrate_page_states(newpage, page); return MIGRATEPAGE_SUCCESS; } #endif -- cgit v1.2.3