commit fdeaf7b867fda0760a1d965496f288401039f092
Author: pliard <pliard@google.com>
Date:   Tue Jul 23 09:54:41 2019 +0900

    Support readahead() calls larger than 32 pages

diff --git a/src/pack.c b/src/pack.c
index 7903870..d7c6c8e 100644
--- a/src/pack.c
+++ b/src/pack.c
@@ -79,6 +79,13 @@
  **/
 #define NUM_THREADS 4
 
+/**
+ * READAHEAD_MAX_LENGTH:
+ *
+ * Maximum length that can be passed to readahead(). On kernels older than v4.10
+ * readahead() reads up to 32 pages regardless of the provided length.
+ **/
+#define READAHEAD_MAX_LENGTH (32 * 4096)
 
 typedef enum pack_flags {
 	PACK_ROTATIONAL = 0x01,
@@ -221,6 +228,23 @@ pack_file_name_for_device (const void *parent,
 	nih_return_system_error (NULL);
 }
 
+static int
+load_pages_in_core (int   fd,
+		    off_t offset,
+		    off_t length)
+{
+	while (length > 0) {
+		const off_t read_length = length <= READAHEAD_MAX_LENGTH ?
+			length : READAHEAD_MAX_LENGTH;
+		int ret = readahead (fd, offset, read_length);
+		if (ret < 0) {
+			return ret;
+		}
+		offset += read_length;
+		length -= read_length;
+	}
+	return 0;
+}
 
 PackFile *
 read_pack (const void *parent,
@@ -246,7 +270,7 @@ read_pack (const void *parent,
 
 	/* Obvious really... */
 	if (fstat (fileno (fp), &stat) == 0)
-		readahead (fileno (fp), 0, stat.st_size);
+		load_pages_in_core (fileno (fp), 0, stat.st_size);
 
 	file = NIH_MUST (nih_new (parent, PackFile));
 
@@ -744,9 +768,9 @@ do_readahead_hdd (PackFile *file,
 		    || (file->blocks[i].pathidx >= file->num_paths))
 			continue;
 
-		readahead (fds[file->blocks[i].pathidx],
-			   file->blocks[i].offset,
-			   file->blocks[i].length);
+		load_pages_in_core (fds[file->blocks[i].pathidx],
+				    file->blocks[i].offset,
+				    file->blocks[i].length);
 	}
 
 	print_time ("Readahead", &start);
@@ -859,9 +883,9 @@ ra_thread (void *ptr)
 		}
 
 		do {
-			readahead (fd,
-				   ctx->file->blocks[i].offset,
-				   ctx->file->blocks[i].length);
+			load_pages_in_core (fd,
+					    ctx->file->blocks[i].offset,
+					    ctx->file->blocks[i].length);
 		} while ((++i < ctx->file->num_blocks)
 			 && (ctx->file->blocks[i].pathidx == pathidx));
 	}