linux-kernel - Re: [PATCH RESEND v1 01/16] vfs: introduce some data structures

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Date:	Thu, 10 Jan 2013 01:48:18 +0100
From:	David Sterba <dsterba@...e.cz>
To:	zwu.kernel@...il.com
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	viro@...iv.linux.org.uk, david@...morbit.com,
	darrick.wong@...cle.com, andi@...stfloor.org, hch@...radead.org,
	linuxram@...ux.vnet.ibm.com, wuzhy@...ux.vnet.ibm.com
Subject: Re: [PATCH RESEND v1 01/16] vfs: introduce some data structures

On Thu, Dec 20, 2012 at 10:43:20PM +0800, zwu.kernel@...il.com wrote:
> --- /dev/null
> +++ b/fs/hot_tracking.c
> @@ -0,0 +1,109 @@
> +/*
> + * fs/hot_tracking.c

>From what I've undrestood the file name written here is not wanted, so
please drop it (and from .h too)

> + *
> + * Copyright (C) 2012 IBM Corp. All rights reserved.
> + * Written by Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public
> + * License v2 as published by the Free Software Foundation.

A short description of the hot tracking feature or pointer to the
Documentation/ file would be nice here.

> + */
> +
> +#include <linux/list.h>
> +#include <linux/err.h>
> +#include <linux/slab.h>
> +#include <linux/module.h>
> +#include <linux/spinlock.h>
> +#include <linux/hardirq.h>
> +#include <linux/fs.h>
> +#include <linux/blkdev.h>
> +#include <linux/types.h>
> +#include <linux/limits.h>
> +#include "hot_tracking.h"
> +
> +/* kmem_cache pointers for slab caches */

This comment seems useless to me, I does not help understanding the code, just
says the same what reads in C. There are more such redundant comments in the
series, but I'm not going point to all of them right now.

> +static struct kmem_cache *hot_inode_item_cachep __read_mostly;
> +static struct kmem_cache *hot_range_item_cachep __read_mostly;
> +

> --- /dev/null
> +++ b/include/linux/hot_tracking.h
> +/* The common info for both following structures */
> +struct hot_comm_item {
> +	struct rb_node rb_node; /* rbtree index */
> +	struct hot_freq_data hot_freq_data;  /* frequency data */
> +	spinlock_t lock; /* protects object data */
> +	struct kref refs;  /* prevents kfree */
> +};
> +
> +/* An item representing an inode and its access frequency */
> +struct hot_inode_item {
> +	struct hot_comm_item hot_inode; /* node in hot_inode_tree */
> +	struct hot_rb_tree hot_range_tree; /* tree of ranges */
> +	spinlock_t lock; /* protect range tree */
> +	struct hot_rb_tree *hot_inode_tree;
> +	u64 i_ino; /* inode number from inode */
> +};

Please align the comments to something like this (or drop them if they seem
redundant):

/* The common info for both following structures */
struct hot_comm_item {
        struct rb_node rb_node;              /* rbtree index */
        struct hot_freq_data hot_freq_data;  /* frequency data */
        spinlock_t lock;                     /* protects object data */
        struct kref refs;                    /* prevents kfree */
        struct list_head n_list;             /* list node index */
};

/* An item representing an inode and its access frequency */
struct hot_inode_item {
        struct hot_comm_item hot_inode;      /* node in hot_inode_tree */
        struct hot_rb_tree hot_range_tree;   /* tree of ranges */
        spinlock_t lock;                     /* protect range tree */
        struct hot_rb_tree *hot_inode_tree;
        u64 i_ino;                           /* inode number from inode */
};

> +extern void __init hot_cache_init(void);

this belongs to the private include fs/hot_tracking.h (because this is called
only once by vfs init and not by filesystems), there's
hot_track_init(superblock) for that purpose introduced later.


david
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