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Date:	Tue, 25 Sep 2012 17:54:01 +0800
From:	Ram Pai <linuxram@...ibm.com>
To:	zwu.kernel@...il.com
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org,
	linuxram@...ux.vnet.ibm.com, viro@...iv.linux.org.uk,
	cmm@...ibm.com, tytso@....edu, marco.stornelli@...il.com,
	david@...morbit.com, stroetmann@...olinux.com, diegocg@...il.com,
	chris@...muel.org, Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
Subject: Re: [RFC v2 05/10] vfs: introduce one hash table

On Sun, Sep 23, 2012 at 08:56:30PM +0800, zwu.kernel@...il.com wrote:
> From: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
> 
>   Adds a hash table structure which contains
> a lot of hash list and is used to efficiently
> look up the data temperature of a file or its
> ranges.
>   In each hash list of hash table, the hash node
> will keep track of temperature info.
> 
> Signed-off-by: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
> ---
>  fs/hot_tracking.c            |   77 ++++++++++++++++++++++++++++++++++++++++-
>  include/linux/hot_tracking.h |   35 +++++++++++++++++++
>  2 files changed, 110 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
> index fa89f70..5f96442 100644
> --- a/fs/hot_tracking.c
> +++ b/fs/hot_tracking.c
> @@ -16,6 +16,7 @@
>  #include <linux/module.h>
>  #include <linux/spinlock.h>
>  #include <linux/hardirq.h>
> +#include <linux/hash.h>
>  #include <linux/fs.h>
>  #include <linux/blkdev.h>
>  #include <linux/types.h>
> @@ -24,6 +25,9 @@

...snip...

> +/* Hash list heads for hot hash table */
> +struct hot_hash_head {
> +	struct hlist_head hashhead;
> +	rwlock_t rwlock;
> +	u32 temperature;
> +};
> +
> +/* Nodes stored in each hash list of hash table */
> +struct hot_hash_node {
> +	struct hlist_node hashnode;
> +	struct list_head node;
> +	struct hot_freq_data *hot_freq_data;
> +	struct hot_hash_head *hlist;
> +	spinlock_t lock; /* protects hlist */
> +
> +	/*
> +	 * number of references to this node
> +	 * equals 1 (hashlist entry)
> +	 */
> +	struct kref refs;
> +};

Dont see why you need yet another datastructure to hash the inode_item
and the range_item into a hash list.  You can just add another
hlist_node in the inode_item and range_item. This field can be then used
to link into the corresponding hash list.

You can use the container_of() get to the inode_item or the range_item
using the hlist_node field. 

You can thus eliminate a lot of code.

> +
>  /* An item representing an inode and its access frequency */
>  struct hot_inode_item {
>  	/* node for hot_inode_tree rb_tree */
> @@ -68,6 +93,8 @@ struct hot_inode_item {
>  	spinlock_t lock;
>  	/* prevents kfree */
>  	struct kref refs;
> +	/* hashlist node for this inode */
> +	struct hot_hash_node *heat_node;

this can be just
	struct hlist_node head_node; /* lookup hot_inode hash list */

Use this field to link it into the corresponding hashlist.

>  };
> 
this can be just 
>  /*
> @@ -91,6 +118,8 @@ struct hot_range_item {
>  	spinlock_t lock;
>  	/* prevents kfree */
>  	struct kref refs;
> +	/* hashlist node for this range */
> +	struct hot_hash_node *heat_node;

this can be just 
	struct hlist_node head_node; /* lookup hot_range hash list */


>  };
> 
>  struct hot_info {
> @@ -98,6 +127,12 @@ struct hot_info {
> 
>  	/* red-black tree that keeps track of fs-wide hot data */
>  	struct hot_inode_tree hot_inode_tree;
> +
> +	/* hash map of inode temperature */
> +	struct hot_hash_head heat_inode_hl[HEAT_HASH_SIZE];
> +
> +	/* hash map of range temperature */
> +	struct hot_hash_head heat_range_hl[HEAT_HASH_SIZE];
>  };
> 
>  #endif  /* _LINUX_HOTTRACK_H */

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