udf: add extent cache support in case of file reading

This patch implements extent caching in case of file reading.
While reading a file, currently, UDF reads metadata serially
which takes a lot of time depending on the number of extents present
in the file. Caching last accessd extent improves metadata read time.
Instead of reading file metadata from start, now we read from
the cached extent.

This patch considerably improves the time spent by CPU in kernel mode.
For example, while reading a 10.9 GB file using dd:
Time before applying patch:
11677022208 bytes (10.9GB) copied, 1529.748921 seconds, 7.3MB/s
real 25m 29.85s
user 0m 12.41s
sys 15m 34.75s

Time after applying patch:
11677022208 bytes (10.9GB) copied, 1469.338231 seconds, 7.6MB/s
real 24m 29.44s
user 0m 15.73s
sys 3m 27.61s

[JK: Fix bh refcounting issues, simplify initialization]

Signed-off-by: Namjae Jeon <[e-mail]>
Signed-off-by: Ashish Sangwan <[e-mail]>
Signed-off-by: Bonggil Bak <[e-mail]>
Signed-off-by: Jan Kara <[e-mail]>

fs/udf/inode.c

···
 			       struct extent_position *);
 static int udf_get_block(struct inode *, sector_t, struct buffer_head *, int);
 
+static void __udf_clear_extent_cache(struct inode *inode)
+{
+	struct udf_inode_info *iinfo = UDF_I(inode);
+
+	if (iinfo->cached_extent.lstart != -1) {
+		brelse(iinfo->cached_extent.epos.bh);
+		iinfo->cached_extent.lstart = -1;
+	}
+}
+
+/* Invalidate extent cache */
+static void udf_clear_extent_cache(struct inode *inode)
+{
+	struct udf_inode_info *iinfo = UDF_I(inode);
+
+	spin_lock(&iinfo->i_extent_cache_lock);
+	__udf_clear_extent_cache(inode);
+	spin_unlock(&iinfo->i_extent_cache_lock);
+}
+
+/* Return contents of extent cache */
+static int udf_read_extent_cache(struct inode *inode, loff_t bcount,
+				 loff_t *lbcount, struct extent_position *pos)
+{
+	struct udf_inode_info *iinfo = UDF_I(inode);
+	int ret = 0;
+
+	spin_lock(&iinfo->i_extent_cache_lock);
+	if ((iinfo->cached_extent.lstart <= bcount) &&
+	    (iinfo->cached_extent.lstart != -1)) {
+		/* Cache hit */
+		*lbcount = iinfo->cached_extent.lstart;
+		memcpy(pos, &iinfo->cached_extent.epos,
+		       sizeof(struct extent_position));
+		if (pos->bh)
+			get_bh(pos->bh);
+		ret = 1;
+	}
+	spin_unlock(&iinfo->i_extent_cache_lock);
+	return ret;
+}
+
+/* Add extent to extent cache */
+static void udf_update_extent_cache(struct inode *inode, loff_t estart,
+				    struct extent_position *pos, int next_epos)
+{
+	struct udf_inode_info *iinfo = UDF_I(inode);
+
+	spin_lock(&iinfo->i_extent_cache_lock);
+	/* Invalidate previously cached extent */
+	__udf_clear_extent_cache(inode);
+	if (pos->bh)
+		get_bh(pos->bh);
+	memcpy(&iinfo->cached_extent.epos, pos,
+	       sizeof(struct extent_position));
+	iinfo->cached_extent.lstart = estart;
+	if (next_epos)
+		switch (iinfo->i_alloc_type) {
+		case ICBTAG_FLAG_AD_SHORT:
+			iinfo->cached_extent.epos.offset -=
+			sizeof(struct short_ad);
+			break;
+		case ICBTAG_FLAG_AD_LONG:
+			iinfo->cached_extent.epos.offset -=
+			sizeof(struct long_ad);
+		}
+	spin_unlock(&iinfo->i_extent_cache_lock);
+}
 
 void udf_evict_inode(struct inode *inode)
 {
···
 	}
 	kfree(iinfo->i_ext.i_data);
 	iinfo->i_ext.i_data = NULL;
+	udf_clear_extent_cache(inode);
 	if (want_delete) {
 		udf_free_inode(inode);
 	}
···
 		truncate_pagecache(inode, to, isize);
 		if (iinfo->i_alloc_type != ICBTAG_FLAG_AD_IN_ICB) {
 			down_write(&iinfo->i_data_sem);
+			udf_clear_extent_cache(inode);
 			udf_truncate_extents(inode);
 			up_write(&iinfo->i_data_sem);
 		}
···
 		iinfo->i_next_alloc_goal++;
 	}
 
-
+	udf_clear_extent_cache(inode);
 	phys = inode_getblk(inode, block, &err, &new);
 	if (!phys)
 		goto abort;
···
 	} else {
 		if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB) {
 			down_write(&iinfo->i_data_sem);
+			udf_clear_extent_cache(inode);
 			memset(iinfo->i_ext.i_data + iinfo->i_lenEAttr + newsize,
 			       0x00, bsize - newsize -
 			       udf_file_entry_alloc_offset(inode));
···
 		if (err)
 			return err;
 		down_write(&iinfo->i_data_sem);
+		udf_clear_extent_cache(inode);
 		truncate_setsize(inode, newsize);
 		udf_truncate_extents(inode);
 		up_write(&iinfo->i_data_sem);
···
 	struct udf_inode_info *iinfo;
 
 	iinfo = UDF_I(inode);
-	pos->offset = 0;
-	pos->block = iinfo->i_location;
-	pos->bh = NULL;
+	if (!udf_read_extent_cache(inode, bcount, &lbcount, pos)) {
+		pos->offset = 0;
+		pos->block = iinfo->i_location;
+		pos->bh = NULL;
+	}
 	*elen = 0;
-
 	do {
 		etype = udf_next_aext(inode, pos, eloc, elen, 1);
 		if (etype == -1) {
···
 		}
 		lbcount += *elen;
 	} while (lbcount <= bcount);
-
+	/* update extent cache */
+	udf_update_extent_cache(inode, lbcount - *elen, pos, 1);
 	*offset = (bcount + *elen - lbcount) >> blocksize_bits;
 
 	return etype;

fs/udf/super.c

···
 	ei->i_next_alloc_goal = 0;
 	ei->i_strat4096 = 0;
 	init_rwsem(&ei->i_data_sem);
+	ei->cached_extent.lstart = -1;
+	spin_lock_init(&ei->i_extent_cache_lock);
 
 	return &ei->vfs_inode;
 }

fs/udf/udf_i.h

···
 #ifndef _UDF_I_H
 #define _UDF_I_H
 
+struct extent_position {
+	struct buffer_head *bh;
+	uint32_t offset;
+	struct kernel_lb_addr block;
+};
+
+struct udf_ext_cache {
+	/* Extent position */
+	struct extent_position epos;
+	/* Start logical offset in bytes */
+	loff_t lstart;
+};
+
 /*
  * The i_data_sem and i_mutex serve for protection of allocation information
  * of a regular files and symlinks. This includes all extents belonging to
···
 		__u8		*i_data;
 	} i_ext;
 	struct rw_semaphore	i_data_sem;
+	struct udf_ext_cache cached_extent;
+	/* Spinlock for protecting extent cache */
+	spinlock_t i_extent_cache_lock;
 	struct inode vfs_inode;
 };
 

fs/udf/udfdecl.h

···
 	uint8_t u_len;
 };
 
-struct extent_position {
-	struct buffer_head *bh;
-	uint32_t offset;
-	struct kernel_lb_addr block;
-};
 
 /* super.c */