mm, fadvise: improve the expensive remote LRU cache draining after FADV_DONTNEED

Our users reported that there're some random latency spikes when their RT
process is running.  Finally we found that latency spike is caused by
FADV_DONTNEED.  Which may call lru_add_drain_all() to drain LRU cache on
remote CPUs, and then waits the per-cpu work to complete.  The wait time
is uncertain, which may be tens millisecond.

That behavior is unreasonable, because this process is bound to a specific
CPU and the file is only accessed by itself, IOW, there should be no
pagecache pages on a per-cpu pagevec of a remote CPU.  That unreasonable
behavior is partially caused by the wrong comparation of the number of
invalidated pages and the number of the target.  For example,

        if (count < (end_index - start_index + 1))

The count above is how many pages were invalidated in the local CPU, and
(end_index - start_index + 1) is how many pages should be invalidated.
The usage of (end_index - start_index + 1) is incorrect,...

include/linux/fs.h

@@ -2581,6 +2581,10 @@ extern bool is_bad_inode(struct inode *);
 unsigned long invalidate_mapping_pages(struct address_space *mapping,
 					pgoff_t start, pgoff_t end);
 
+void invalidate_mapping_pagevec(struct address_space *mapping,
+				pgoff_t start, pgoff_t end,
+				unsigned long *nr_pagevec);
+
 static inline void invalidate_remote_inode(struct inode *inode)
 {
 	if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||

mm/fadvise.c

@@ -141,7 +141,7 @@ int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 		}
 
 		if (end_index >= start_index) {
-			unsigned long count;
+			unsigned long nr_pagevec = 0;
 
 			/*
 			 * It's common to FADV_DONTNEED right after
@@ -154,8 +154,9 @@ int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 			 */
 			lru_add_drain();
 
-			count = invalidate_mapping_pages(mapping,
-						start_index, end_index);
+			invalidate_mapping_pagevec(mapping,
+						start_index, end_index,
+						&nr_pagevec);
 
 			/*
 			 * If fewer pages were invalidated than expected then
@@ -163,7 +164,7 @@ int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 			 * a per-cpu pagevec for a remote CPU. Drain all
 			 * pagevecs and try again.
 			 */
-			if (count < (end_index - start_index + 1)) {
+			if (nr_pagevec) {
 				lru_add_drain_all();
 				invalidate_mapping_pages(mapping, start_index,
 						end_index);

mm/truncate.c

@@ -528,23 +528,8 @@ void truncate_inode_pages_final(struct address_space *mapping)
 }
 EXPORT_SYMBOL(truncate_inode_pages_final);
 
-/**
- * invalidate_mapping_pages - Invalidate all the unlocked pages of one inode
- * @mapping: the address_space which holds the pages to invalidate
- * @start: the offset 'from' which to invalidate
- * @end: the offset 'to' which to invalidate (inclusive)
- *
- * This function only removes the unlocked pages, if you want to
- * remove all the pages of one inode, you must call truncate_inode_pages.
- *
- * invalidate_mapping_pages() will not block on IO activity. It will not
- * invalidate pages which are dirty, locked, under writeback or mapped into
- * pagetables.
- *
- * Return: the number of the pages that were invalidated
- */
-unsigned long invalidate_mapping_pages(struct address_space *mapping,
-		pgoff_t start, pgoff_t end)
+unsigned long __invalidate_mapping_pages(struct address_space *mapping,
+		pgoff_t start, pgoff_t end, unsigned long *nr_pagevec)
 {
 	pgoff_t indices[PAGEVEC_SIZE];
 	struct pagevec pvec;
@@ -610,8 +595,13 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
 			 * Invalidation is a hint that the page is no longer
 			 * of interest and try to speed up its reclaim.
 			 */
-			if (!ret)
+			if (!ret) {
 				deactivate_file_page(page);
+				/* It is likely on the pagevec of a remote CPU */
+				if (nr_pagevec)
+					(*nr_pagevec)++;
+			}
+
 			if (PageTransHuge(page))
 				put_page(page);
 			count += ret;
@@ -623,8 +613,40 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
 	}
 	return count;
 }
+
+/**
+ * invalidate_mapping_pages - Invalidate all the unlocked pages of one inode
+ * @mapping: the address_space which holds the pages to invalidate
+ * @start: the offset 'from' which to invalidate
+ * @end: the offset 'to' which to invalidate (inclusive)
+ *
+ * This function only removes the unlocked pages, if you want to
+ * remove all the pages of one inode, you must call truncate_inode_pages.
+ *
+ * invalidate_mapping_pages() will not block on IO activity. It will not
+ * invalidate pages which are dirty, locked, under writeback or mapped into
+ * pagetables.
+ *
+ * Return: the number of the pages that were invalidated
+ */
+unsigned long invalidate_mapping_pages(struct address_space *mapping,
+		pgoff_t start, pgoff_t end)
+{
+	return __invalidate_mapping_pages(mapping, start, end, NULL);
+}
 EXPORT_SYMBOL(invalidate_mapping_pages);
 
+/**
+ * This helper is similar with the above one, except that it accounts for pages
+ * that are likely on a pagevec and count them in @nr_pagevec, which will used by
+ * the caller.
+ */
+void invalidate_mapping_pagevec(struct address_space *mapping,
+		pgoff_t start, pgoff_t end, unsigned long *nr_pagevec)
+{
+	__invalidate_mapping_pages(mapping, start, end, nr_pagevec);
+}
+
 /*
  * This is like invalidate_complete_page(), except it ignores the page's
  * refcount.  We do this because invalidate_inode_pages2() needs stronger