linux-kernel - Re: [PATCH] udf: add extent cache support in case of file reading

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Date:	Mon, 21 Jan 2013 12:04:42 +0100
From:	Jan Kara <jack@...e.cz>
To:	Namjae Jeon <linkinjeon@...il.com>
Cc:	jack@...e.cz, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Namjae Jeon <namjae.jeon@...sung.com>,
	Ashish Sangwan <a.sangwan@...sung.com>,
	Bonggil Bak <bgbak@...sung.com>
Subject: Re: [PATCH] udf: add extent cache support in case of file reading

On Sat 19-01-13 11:17:14, Namjae Jeon wrote:
> From: Namjae Jeon <namjae.jeon@...sung.com>
> 
> 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
> 
> Signed-off-by: Namjae Jeon <namjae.jeon@...sung.com>
> Signed-off-by: Ashish Sangwan <a.sangwan@...sung.com>
> Signed-off-by: Bonggil Bak <bgbak@...sung.com>
  Thanks for the patch Namjae. I did a few more changes to the patch.
Please check them whether you think they are OK.

diff --git a/fs/udf/ialloc.c b/fs/udf/ialloc.c
index 0cb208e..7e5aae4 100644
--- a/fs/udf/ialloc.c
+++ b/fs/udf/ialloc.c
@@ -117,10 +117,6 @@ struct inode *udf_new_inode(struct inode *dir, umode_t mode, int *err)
 	iinfo->i_lenAlloc = 0;
 	iinfo->i_use = 0;
 	iinfo->i_checkpoint = 1;
-	memset(&iinfo->cached_extent, 0, sizeof(struct udf_ext_cache));
-	spin_lock_init(&(iinfo->i_extent_cache_lock));
-	/* Mark extent cache as invalid for now */
-	iinfo->cached_extent.lstart = -1;
 	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_AD_IN_ICB))
 		iinfo->i_alloc_type = ICBTAG_FLAG_AD_IN_ICB;
 	else if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_SHORT_AD))
diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index 8494b8c..fb0c4c4 100644
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -1305,9 +1305,6 @@ static void udf_fill_inode(struct inode *inode, struct buffer_head *bh)
 	iinfo->i_lenAlloc = 0;
 	iinfo->i_next_alloc_block = 0;
 	iinfo->i_next_alloc_goal = 0;
-	memset(&iinfo->cached_extent, 0, sizeof(struct udf_ext_cache));
-	spin_lock_init(&(iinfo->i_extent_cache_lock));
-	iinfo->cached_extent.lstart = -1;
 	if (fe->descTag.tagIdent == cpu_to_le16(TAG_IDENT_EFE)) {
 		iinfo->i_efe = 1;
 		iinfo->i_use = 0;

  Initialization now happens in udf_alloc_inode(). Also it's not necessary
to initialized cached_extent.epos when lstart == -1 - noone should look at
that.

@@ -2222,6 +2219,8 @@ int udf_read_extent_cache(struct inode *inode, loff_t bcount,
 		*lbcount = iinfo->cached_extent.lstart;
 		memcpy(pos, &iinfo->cached_extent.epos,
 		       sizeof(struct extent_position));
+		if (pos->bh)
+			get_bh(pos->bh);
 		spin_unlock(&iinfo->i_extent_cache_lock);
 		return 1;
 	} else
  This is the most important - we should give buffer reference to pos->bh.
Caller will eventually free it right?

@@ -2236,8 +2235,7 @@ void udf_update_extent_cache(struct inode *inode, loff_t estart,
 	struct udf_inode_info *iinfo = UDF_I(inode);
 
 	spin_lock(&iinfo->i_extent_cache_lock);
-	if (pos->bh != NULL)
-		/* Increase ref count */
+	if (pos->bh)
 		get_bh(pos->bh);
 	memcpy(&iinfo->cached_extent.epos, pos,
 	       sizeof(struct extent_position));
@@ -2266,4 +2264,3 @@ void udf_clear_extent_cache(struct udf_inode_info *iinfo)
 		iinfo->cached_extent.lstart = -1;
 	}
 }
-
diff --git a/fs/udf/super.c b/fs/udf/super.c
index 186adbf..da8ce9f 100644
--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -134,6 +134,8 @@ static struct inode *udf_alloc_inode(struct super_block *sb)
 	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;
 }

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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