[patch 24/26] mm/thp: allow dropping THP from page cache

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From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Subject: 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@xxxxxx
Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Song Liu <songliubraving@xxxxxx>
Tested-by: Song Liu <songliubraving@xxxxxx>
Acked-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
Cc: William Kucharski <william.kucharski@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/truncate.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/mm/truncate.c~mm-thp-allow-drop-thp-from-page-cache
+++ a/mm/truncate.c
@@ -592,6 +592,16 @@ unsigned long invalidate_mapping_pages(s
 					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(s
 			 */
 			if (!ret)
 				deactivate_file_page(page);
+			if (PageTransHuge(page))
+				put_page(page);
 			count += ret;
 		}
 		pagevec_remove_exceptionals(&pvec);
_



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