linux-ext4 - [PATCH 1/3] ext2fs: add readahead method to improve scanning

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Message-ID: <20140201103727.9011.91402.stgit@birch.djwong.org>
Date:	Sat, 01 Feb 2014 02:37:27 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	tytso@....edu, darrick.wong@...cle.com
Cc:	linux-ext4@...r.kernel.org,
	Andreas Dilger <andreas.dilger@...el.com>
Subject: [PATCH 1/3] ext2fs: add readahead method to improve scanning

Frøm: Andreas Dilger <adilger@...mcloud.com>

Add a readahead method for prefetching ranges of disk blocks.
This is useful for inode table scanning, and other large
contiguous ranges of blocks, and may also prove useful for
random block prefetch, since it will allow reordering of the
IO without waiting synchronously for the reads to complete.

It is currently using the posix_fadvise(POSIX_FADV_WILLNEED)
interface, as this proved most efficient during our testing

[darrick.wong@...cle.com]
Make the arguments to the readahead function take the same
ULL values as the other IO functions, and return an
appropriate error code when fadvise isn't available.

Signed-off-by: Andreas Dilger <andreas.dilger@...el.com>
Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
---
 lib/ext2fs/ext2_io.h    |    4 ++++
 lib/ext2fs/io_manager.c |    9 +++++++++
 lib/ext2fs/unix_io.c    |   28 +++++++++++++++++++++++++---
 3 files changed, 38 insertions(+), 3 deletions(-)


diff --git a/lib/ext2fs/ext2_io.h b/lib/ext2fs/ext2_io.h
index 1894fb8..00e22e0 100644
--- a/lib/ext2fs/ext2_io.h
+++ b/lib/ext2fs/ext2_io.h
@@ -90,6 +90,8 @@ struct struct_io_manager {
 					int count, const void *data);
 	errcode_t (*discard)(io_channel channel, unsigned long long block,
 			     unsigned long long count);
+	errcode_t (*readahead)(io_channel channel, unsigned long long block,
+			       unsigned long long count);
 	long	reserved[16];
 };
 
@@ -124,6 +126,8 @@ extern errcode_t io_channel_discard(io_channel channel,
 				    unsigned long long count);
 extern errcode_t io_channel_alloc_buf(io_channel channel,
 				      int count, void *ptr);
+extern errcode_t io_channel_readahead(io_channel io, unsigned long long block,
+				      unsigned long long count);
 
 /* unix_io.c */
 extern io_manager unix_io_manager;
diff --git a/lib/ext2fs/io_manager.c b/lib/ext2fs/io_manager.c
index 34e4859..1acbb1d 100644
--- a/lib/ext2fs/io_manager.c
+++ b/lib/ext2fs/io_manager.c
@@ -128,3 +128,12 @@ errcode_t io_channel_alloc_buf(io_channel io, int count, void *ptr)
 	else
 		return ext2fs_get_mem(size, ptr);
 }
+
+errcode_t io_channel_readahead(io_channel io, unsigned long long block,
+			       unsigned long long count)
+{
+	if (!io->manager->readahead)
+		return EXT2_ET_OP_NOT_SUPPORTED;
+
+	return io->manager->readahead(io, block, nblocks);
+}
diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c
index 0cc0f52..bc4490c 100644
--- a/lib/ext2fs/unix_io.c
+++ b/lib/ext2fs/unix_io.c
@@ -15,6 +15,9 @@
  * %End-Header%
  */
 
+#define _XOPEN_SOURCE 600
+#define _DARWIN_C_SOURCE
+#define _FILE_OFFSET_BITS 64
 #define _LARGEFILE_SOURCE
 #define _LARGEFILE64_SOURCE
 #ifndef _GNU_SOURCE
@@ -35,6 +38,9 @@
 #ifdef __linux__
 #include <sys/utsname.h>
 #endif
+#if HAVE_SYS_TYPES_H
+#include <sys/types.h>
+#endif
 #ifdef HAVE_SYS_IOCTL_H
 #include <sys/ioctl.h>
 #endif
@@ -44,9 +50,6 @@
 #if HAVE_SYS_STAT_H
 #include <sys/stat.h>
 #endif
-#if HAVE_SYS_TYPES_H
-#include <sys/types.h>
-#endif
 #if HAVE_SYS_RESOURCE_H
 #include <sys/resource.h>
 #endif
@@ -119,6 +122,8 @@ static errcode_t unix_write_blk64(io_channel channel, unsigned long long block,
 				int count, const void *data);
 static errcode_t unix_discard(io_channel channel, unsigned long long block,
 			      unsigned long long count);
+static errcode_t unix_readahead(io_channel channel, unsigned long long block,
+				unsigned long long count);
 
 static struct struct_io_manager struct_unix_manager = {
 	EXT2_ET_MAGIC_IO_MANAGER,
@@ -135,6 +140,7 @@ static struct struct_io_manager struct_unix_manager = {
 	unix_read_blk64,
 	unix_write_blk64,
 	unix_discard,
+	unix_readahead,
 };
 
 io_manager unix_io_manager = &struct_unix_manager;
@@ -828,6 +834,22 @@ static errcode_t unix_write_blk64(io_channel channel, unsigned long long block,
 #endif /* NO_IO_CACHE */
 }
 
+static errcode_t unix_readahead(io_channel channel, unsigned long long block,
+				unsigned long long count)
+{
+#ifdef POSIX_FADV_WILLNEED
+	struct unix_private_data *data;
+
+	data = (struct unix_private_data *)channel->private_data;
+	posix_fadvise(data->dev, (ext2_loff_t)block * channel->block_size,
+		      (ext2_loff_t)count * channel->block_size,
+		      POSIX_FADV_WILLNEED);
+	return 0;
+#else
+	return EXT2_ET_OP_NOT_SUPPORTED;
+#endif
+}
+
 static errcode_t unix_write_blk(io_channel channel, unsigned long block,
 				int count, const void *buf)
 {

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