Re: Testing ext4 persistent preallocation patches for 64 bit features

[Mingming Cao <cmm@us.ibm.com>]

On Wed, 2007-02-07 at 13:18 +0530, Amit K. Arora wrote:
> I plan to test the persistent preallocation patches on a huge sparse
> device, to know if >32 bit physical block numbers (upto 48bit) behave as
> expected.
Thanks!


>  I have following questions for this and will appreciate
> suggestions here:

> c) Do I need to put some hack in the filesystem code for above (to
> allocate >32 bit physical block numbers) ?
> 

I had a ext3 hack patch before to allow application specify which block
group is the targeted block allocation group,using ioctl command, so to
allocate >32 bit physical block numbers it just set the target block
group beyond 2**(32-15) = 2**17. patch is below..

BTW, have you considered
- move the preallocation code in ioctl to a seperate function, and call
that function from ioctl? That way we could easily switch to
posix_falloc later.
- Test preallocation with mapped IO?
- disable preallocation if the filesystem free blocks is under some low
watermarks, to save space for near future real block allocation?
- is de-preallocation something worth doing?

Mingming

---

 linux-2.6.16-ming/fs/ext3/balloc.c          |   24 ++++++++++++++---------
 linux-2.6.16-ming/fs/ext3/ioctl.c           |   29 ++++++++++++++++++++++++++++
 linux-2.6.16-ming/include/linux/ext3_fs.h   |    1 
 linux-2.6.16-ming/include/linux/ext3_fs_i.h |    1 
 4 files changed, 46 insertions(+), 9 deletions(-)

diff -puN fs/ext3/ioctl.c~ext3_set_alloc_blk_group_hack fs/ext3/ioctl.c
--- linux-2.6.16/fs/ext3/ioctl.c~ext3_set_alloc_blk_group_hack	2006-03-28 15:19:58.000000000 -0800
+++ linux-2.6.16-ming/fs/ext3/ioctl.c	2006-03-28 15:54:14.507288400 -0800
@@ -22,6 +22,7 @@ int ext3_ioctl (struct inode * inode, st
 	struct ext3_inode_info *ei = EXT3_I(inode);
 	unsigned int flags;
 	unsigned short rsv_window_size;
+	unsigned int blk_group;
 
 	ext3_debug ("cmd = %u, arg = %lu\n", cmd, arg);
 
@@ -193,6 +194,34 @@ flags_err:
 		mutex_unlock(&ei->truncate_mutex);
 		return 0;
 	}
+	case EXT3_IOC_SETALLOCBLKGRP: {
+
+		if (!test_opt(inode->i_sb, RESERVATION) ||!S_ISREG(inode->i_mode))
+			return -ENOTTY;
+
+		if (IS_RDONLY(inode))
+			return -EROFS;
+
+		if ((current->fsuid != inode->i_uid) && !capable(CAP_FOWNER))
+			return -EACCES;
+
+		if (get_user(blk_group, (int __user *)arg))
+			return -EFAULT;
+
+		/*
+		 * need to allocate reservation structure for this inode
+		 * before set the window size
+		 */
+		mutex_lock(&ei->truncate_mutex);
+		if (!ei->i_block_alloc_info)
+			ext3_init_block_alloc_info(inode);
+
+		if (ei->i_block_alloc_info){
+			ei->i_block_alloc_info->goal_block_group = blk_group;
+		}
+		mutex_unlock(&ei->truncate_mutex);
+		return 0;
+	}
 	case EXT3_IOC_GROUP_EXTEND: {
 		unsigned long n_blocks_count;
 		struct super_block *sb = inode->i_sb;
diff -puN include/linux/ext3_fs.h~ext3_set_alloc_blk_group_hack include/linux/ext3_fs.h
--- linux-2.6.16/include/linux/ext3_fs.h~ext3_set_alloc_blk_group_hack	2006-03-28 15:42:51.000000000 -0800
+++ linux-2.6.16-ming/include/linux/ext3_fs.h	2006-03-28 15:51:48.321237417 -0800
@@ -238,6 +238,7 @@ struct ext3_new_group_data {
 #endif
 #define EXT3_IOC_GETRSVSZ		_IOR('f', 5, long)
 #define EXT3_IOC_SETRSVSZ		_IOW('f', 6, long)
+#define EXT3_IOC_SETALLOCBLKGRP		_IOW('f', 9, long)
 
 /*
  *  Mount options
diff -puN include/linux/ext3_fs_i.h~ext3_set_alloc_blk_group_hack include/linux/ext3_fs_i.h
--- linux-2.6.16/include/linux/ext3_fs_i.h~ext3_set_alloc_blk_group_hack	2006-03-28 15:43:59.000000000 -0800
+++ linux-2.6.16-ming/include/linux/ext3_fs_i.h	2006-03-28 15:47:54.274367219 -0800
@@ -51,6 +51,7 @@ struct ext3_block_alloc_info {
 	 * allocation when we detect linearly ascending requests.
 	 */
 	__u32                   last_alloc_physical_block;
+	__u32			goal_block_group;
 };
 
 #define rsv_start rsv_window._rsv_start
diff -puN fs/ext3/balloc.c~ext3_set_alloc_blk_group_hack fs/ext3/balloc.c
--- linux-2.6.16/fs/ext3/balloc.c~ext3_set_alloc_blk_group_hack	2006-03-28 15:45:30.000000000 -0800
+++ linux-2.6.16-ming/fs/ext3/balloc.c	2006-03-28 16:03:55.770850040 -0800
@@ -285,6 +285,7 @@ void ext3_init_block_alloc_info(struct i
 		rsv->rsv_alloc_hit = 0;
 		block_i->last_alloc_logical_block = 0;
 		block_i->last_alloc_physical_block = 0;
+		block_i->goal_block_group = 0;
 	}
 	ei->i_block_alloc_info = block_i;
 }
@@ -1263,15 +1264,20 @@ unsigned long ext3_new_blocks(handle_t *
 		*errp = -ENOSPC;
 		goto out;
 	}
-
-	/*
-	 * First, test whether the goal block is free.
-	 */
-	if (goal < le32_to_cpu(es->s_first_data_block) ||
-	    goal >= le32_to_cpu(es->s_blocks_count))
-		goal = le32_to_cpu(es->s_first_data_block);
-	group_no = (goal - le32_to_cpu(es->s_first_data_block)) /
-			EXT3_BLOCKS_PER_GROUP(sb);
+	if (block_i->goal_block_group) {
+		group_no = block_i->goal_block_group;
+		goal = le32_to_cpu(EXT3_SB(sb)->s_es->s_first_data_block) +                                group_no * EXT3_BLOCKS_PER_GROUP(sb);
+		block_i->goal_block_group = 0;
+	} else {
+		/*
+		 * First, test whether the goal block is free.
+		 */
+		if (goal < le32_to_cpu(es->s_first_data_block) ||
+		    goal >= le32_to_cpu(es->s_blocks_count))
+			goal = le32_to_cpu(es->s_first_data_block);
+		group_no = (goal - le32_to_cpu(es->s_first_data_block)) /
+				EXT3_BLOCKS_PER_GROUP(sb);
+	}
 	gdp = ext3_get_group_desc(sb, group_no, &gdp_bh);
 	if (!gdp)
 		goto io_error;

_