[PATCH] [RFC] mm/fadvise: introduce POSIX_FADV_MLOCK

[Jaegeuk Kim <jaegeuk@kernel.org>]

This patch introduces a new POSIX_FADV_MLOCK which 1) invalidates the range of
cached pages, 2) sets the mapping as inaccessible, 3) POSIX_FADV_WILLNEED loads
pages directly to the inaccessible mapping.

The inaccessible pages will be invalidated by evict_inode or explicit munlock().

Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Christian Brauner <brauner@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
---
 include/uapi/linux/fadvise.h |  2 ++
 mm/fadvise.c                 | 14 ++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/include/uapi/linux/fadvise.h b/include/uapi/linux/fadvise.h
index 0862b87434c2..06018688b99b 100644
--- a/include/uapi/linux/fadvise.h
+++ b/include/uapi/linux/fadvise.h
@@ -19,4 +19,6 @@
 #define POSIX_FADV_NOREUSE	5 /* Data will be accessed once.  */
 #endif
 
+#define POSIX_FADV_MLOCK	8 /* Load pages into inaccessible map.  */
+
 #endif	/* FADVISE_H_INCLUDED */
diff --git a/mm/fadvise.c b/mm/fadvise.c
index 588fe76c5a14..849b151d2024 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c
@@ -56,6 +56,7 @@ int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 		case POSIX_FADV_WILLNEED:
 		case POSIX_FADV_NOREUSE:
 		case POSIX_FADV_DONTNEED:
+		case POSIX_FADV_MLOCK:
 			/* no bad return value, but ignore advice */
 			break;
 		default:
@@ -93,6 +94,19 @@ int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 		file->f_mode &= ~FMODE_RANDOM;
 		spin_unlock(&file->f_lock);
 		break;
+	case POSIX_FADV_MLOCK:
+		/* Remove the cached pages. */
+		if (!mapping_unevictable(mapping)) {
+			invalidate_inode_pages2_range(mapping,
+					offset >> PAGE_SHIFT,
+					(offset + len - 1) >> PAGE_SHIFT);
+
+			/* set the mapping is unevictable */
+			filemap_invalidate_lock(mapping);
+			mapping_set_inaccessible(mapping);
+			filemap_invalidate_unlock(mapping);
+		}
+		fallthrough;
 	case POSIX_FADV_WILLNEED:
 		/* First and last PARTIAL page! */
 		start_index = offset >> PAGE_SHIFT;
-- 
2.52.0.487.g5c8c507ade-goog