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: 7b7f7e485f82 ("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>

diff --git a/mm/truncate.c b/mm/truncate.c
index 8563339041f68c4a602ab364f913636071ccda70..dd9ebc1da35664d04dd508539b34fb96dc764f28 100644 (file)
--- 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);