[Devel] [PATCH rh7] fs/fadvise: introduce FADV_DEACTIVATE flag

[Andrey Ryabinin]

FADV_DEACTIVATE advises kernel to move file pages from active to
inactive list.

https://jira.sw.ru/browse/PSBM-57915

Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 include/uapi/linux/fadvise.h |  1 +
 mm/fadvise.c                 | 43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/include/uapi/linux/fadvise.h b/include/uapi/linux/fadvise.h
index a3e0703..b6ade7e 100644
--- a/include/uapi/linux/fadvise.h
+++ b/include/uapi/linux/fadvise.h
@@ -17,6 +17,7 @@
 #define POSIX_FADV_DONTNEED	4 /* Don't need these pages.  */
 #define POSIX_FADV_NOREUSE	5 /* Data will be accessed once.  */
 #endif
+#define FADV_DEACTIVATE		32 /* Mark pages as good candidates for reclaim */
 
 #ifdef __KERNEL__
 extern int generic_fadvise(struct file* file, loff_t off, loff_t len, int adv);
diff --git a/mm/fadvise.c b/mm/fadvise.c
index 2a1bdfb..e805d01 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c
@@ -22,6 +22,43 @@
 
 #include <asm/unistd.h>
 
+static void fadvise_deactivate(struct address_space *mapping,
+		pgoff_t start, pgoff_t end)
+{
+	struct pagevec pvec;
+	pgoff_t index = start;
+	int i;
+
+	if (start > end)
+		return;
+
+	/*
+	 * Note: this function may get called on a shmem/tmpfs mapping:
+	 * pagevec_lookup() might then return 0 prematurely (because it
+	 * got a gangful of swap entries); but it's hardly worth worrying
+	 * about - it can rarely have anything to free from such a mapping
+	 * (most pages are dirty), and already skips over any difficulties.
+	 */
+
+	pagevec_init(&pvec, 0);
+	while (index <= end && pagevec_lookup(&pvec, mapping, index,
+			min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
+		for (i = 0; i < pagevec_count(&pvec); i++) {
+			struct page *page = pvec.pages[i];
+
+			/* We rely upon deletion not changing page->index */
+			index = page->index;
+			if (index > end)
+				break;
+
+			deactivate_page(page);
+		}
+		pagevec_release(&pvec);
+		cond_resched();
+		index++;
+	}
+}
+
 /*
  * POSIX_FADV_WILLNEED could set PG_Referenced, and POSIX_FADV_NOREUSE could
  * deactivate the pages and clear PG_Referenced.
@@ -44,6 +81,7 @@ 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 FADV_DEACTIVATE:
 			/* no bad return value, but ignore advice */
 			break;
 		default:
@@ -124,6 +162,11 @@ int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 			}
 		}
 		break;
+	case FADV_DEACTIVATE:
+		start_index = (offset+(PAGE_CACHE_SIZE-1)) >> PAGE_CACHE_SHIFT;
+		end_index = (endbyte >> PAGE_CACHE_SHIFT);
+		fadvise_deactivate(mapping, start_index, end_index);
+		break;
 	default:
 		ret = -EINVAL;
 	}
-- 
2.10.2