mm/thp: allow dropping THP from page cache

Once a THP is added to the page cache, it cannot be dropped via
/proc/sys/vm/drop_caches.  Fix this issue with proper handling in
invalidate_mapping_pages().

Link: http://lkml.kernel.org/r/20191017164223.2762148-5-songliubraving@fb.com
Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Tested-by: Song Liu <songliubraving@fb.com>
Acked-by: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: William Kucharski <william.kucharski@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/mm/truncate.c b/mm/truncate.c
index 8563339041f6..dd9ebc1da356 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -592,6 +592,16 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
                                         unlock_page(page);
                                         continue;
                                 }
+
+                                /* Take a pin outside pagevec */
+                                get_page(page);
+
+                                /*
+                                 * Drop extra pins before trying to invalidate
+                                 * the huge page.
+                                 */
+                                pagevec_remove_exceptionals(&pvec);
+                                pagevec_release(&pvec);
                         }
 
                         ret = invalidate_inode_page(page);
@@ -602,6 +612,8 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
                          */
                         if (!ret)
                                 deactivate_file_page(page);
+                        if (PageTransHuge(page))
+                                put_page(page);
                         count += ret;
                 }
                 pagevec_remove_exceptionals(&pvec);