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Date:	Wed, 7 Nov 2012 10:58:02 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	Zhi Yong Wu <zwu.kernel@...il.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linuxram@...ux.vnet.ibm.com, viro@...iv.linux.org.uk,
	david@...morbit.com, tytso@....edu, cmm@...ibm.com,
	wuzhy@...ux.vnet.ibm.com, wenqing.lz@...bao.com
Subject: Re: [RFC v4+ hot_track 10/19] vfs: introduce hot func register
 framework

On Wed, Nov 07, 2012 at 04:34:35PM +0800, Zhi Yong Wu wrote:
> On Wed, Nov 7, 2012 at 7:30 AM, Darrick J. Wong <darrick.wong@...cle.com> wrote:
> > On Mon, Oct 29, 2012 at 12:30:52PM +0800, zwu.kernel@...il.com wrote:
> >> From: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
> >>
> >>   Introduce one framwork to enable that specific FS
> >> can register its own hot tracking functions.
> >>
> >> Signed-off-by: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
> >> ---
> >>  fs/hot_tracking.c            |   78 ++++++++++++++++++++++++++++++++++++++----
> >>  include/linux/hot_tracking.h |   25 +++++++++++++
> >>  2 files changed, 96 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
> >> index 0ef9cad..c6c6138 100644
> >> --- a/fs/hot_tracking.c
> >> +++ b/fs/hot_tracking.c
> >> @@ -24,6 +24,9 @@
> >>  #include <linux/limits.h>
> >>  #include "hot_tracking.h"
> >>
> >> +static DEFINE_SPINLOCK(hot_func_list_lock);
> >> +static LIST_HEAD(hot_func_list);
> >> +
> >>  /* kmem_cache pointers for slab caches */
> >>  static struct kmem_cache *hot_inode_item_cachep __read_mostly;
> >>  static struct kmem_cache *hot_range_item_cachep __read_mostly;
> >> @@ -305,20 +308,23 @@ static u64 hot_average_update(struct timespec old_atime,
> >>       return new_avg;
> >>  }
> >>
> >> -static void hot_freq_data_update(struct hot_freq_data *freq_data, bool write)
> >> +static void hot_freq_data_update(struct hot_info *root,
> >> +             struct hot_freq_data *freq_data, bool write)
> >>  {
> >>       struct timespec cur_time = current_kernel_time();
> >>
> >>       if (write) {
> >>               freq_data->nr_writes += 1;
> >> -             freq_data->avg_delta_writes = hot_average_update(
> >> +             freq_data->avg_delta_writes =
> >> +                     root->hot_func_type->ops.hot_rw_freq_calc_fn(
> >>                               freq_data->last_write_time,
> >>                               cur_time,
> >>                               freq_data->avg_delta_writes);
> >>               freq_data->last_write_time = cur_time;
> >>       } else {
> >>               freq_data->nr_reads += 1;
> >> -             freq_data->avg_delta_reads = hot_average_update(
> >> +             freq_data->avg_delta_reads =
> >> +                     root->hot_func_type->ops.hot_rw_freq_calc_fn(
> >>                               freq_data->last_read_time,
> >>                               cur_time,
> >>                               freq_data->avg_delta_reads);
> >> @@ -430,7 +436,7 @@ static void hot_map_array_update(struct hot_freq_data *freq_data,
> >>       struct hot_comm_item *comm_item;
> >>       struct hot_inode_item *he;
> >>       struct hot_range_item *hr;
> >> -     u32 temp = hot_temp_calc(freq_data);
> >> +     u32 temp = root->hot_func_type->ops.hot_temp_calc_fn(freq_data);
> >>       u8 a_temp = temp >> (32 - HEAT_MAP_BITS);
> >>       u8 b_temp = freq_data->last_temp >> (32 - HEAT_MAP_BITS);
> >>
> >> @@ -511,7 +517,7 @@ static void hot_range_update(struct hot_inode_item *he,
> >>                               &hr_nodes[i]->hot_range.hot_freq_data, root);
> >>
> >>                       spin_lock(&hr_nodes[i]->hot_range.lock);
> >> -                     obsolete = hot_is_obsolete(
> >> +                     obsolete = root->hot_func_type->ops.hot_is_obsolete_fn(
> >>                                       &hr_nodes[i]->hot_range.hot_freq_data);
> >>                       spin_unlock(&hr_nodes[i]->hot_range.lock);
> >>
> >> @@ -668,7 +674,7 @@ void hot_update_freqs(struct inode *inode, u64 start,
> >>       }
> >>
> >>       spin_lock(&he->hot_inode.lock);
> >> -     hot_freq_data_update(&he->hot_inode.hot_freq_data, rw);
> >> +     hot_freq_data_update(root, &he->hot_inode.hot_freq_data, rw);
> >>       spin_unlock(&he->hot_inode.lock);
> >>
> >>       /*
> >> @@ -685,7 +691,7 @@ void hot_update_freqs(struct inode *inode, u64 start,
> >>               }
> >>
> >>               spin_lock(&hr->hot_range.lock);
> >> -             hot_freq_data_update(&hr->hot_range.hot_freq_data, rw);
> >> +             hot_freq_data_update(root, &hr->hot_range.hot_freq_data, rw);
> >>               spin_unlock(&hr->hot_range.lock);
> >>
> >>               hot_range_item_put(hr);
> >> @@ -695,6 +701,61 @@ void hot_update_freqs(struct inode *inode, u64 start,
> >>  }
> >>  EXPORT_SYMBOL_GPL(hot_update_freqs);
> >>
> >> +static struct hot_func_type hot_func_def = {
> >> +     .hot_func_name = "hot_type_def",
> >> +     .ops = {
> >> +             .hot_rw_freq_calc_fn = hot_average_update,
> >> +             .hot_temp_calc_fn    = hot_temp_calc,
> >> +             .hot_is_obsolete_fn  = hot_is_obsolete,
> >> +     },
> >> +};
> >
> > If these hot_ops are per-filesystem, why not just embed a struct hot_func_ops
> > inside of struct file_system_type?  That eliminates this _get function,
> this _get function is very small, only some loc, if hot_func_ops is
> embedded in struct file_system_type, i am afraid to introduce some
> regressions....

What kind of regressions are you afraid of, specifically?  I don't think fstype
is performance-critical enough to worry about wreaking havoc in the caches due
to adding three function pointers.

> > collision avoidance, etc.  You can fill in NULL function pointers in
> fill in NULL func pointer? why?
> > hot_track_init (or just code around them).

I guess you could just require that everyone fill out .hot_temp_calc_fn,
even if they just point it to generic_hot_temp_calc.

--D

> >
> > --D
> >
> >> +
> >> +static struct hot_func_type *hot_func_get(const char *name)
> >> +{
> >> +     struct hot_func_type *f, *h = &hot_func_def;
> >> +
> >> +     spin_lock(&hot_func_list_lock);
> >> +     list_for_each_entry(f, &hot_func_list, list) {
> >> +             if (!strcmp(f->hot_func_name, name))
> >> +                     h = f;
> >> +     }
> >> +     spin_unlock(&hot_func_list_lock);
> >> +
> >> +     return h;
> >> +}
> >> +
> >> +int hot_func_register(struct hot_func_type *h)
> >> +{
> >> +     struct hot_func_type *f, *t = NULL;
> >> +
> >> +     /* register, don't allow duplicate names */
> >> +     spin_lock(&hot_func_list_lock);
> >> +     list_for_each_entry(f, &hot_func_list, list) {
> >> +             if (!strcmp(f->hot_func_name, h->hot_func_name))
> >> +                     t = f;
> >> +     }
> >> +
> >> +     if (t) {
> >> +             spin_unlock(&hot_func_list_lock);
> >> +             return -EBUSY;
> >> +     }
> >> +
> >> +     list_add_tail(&h->list, &hot_func_list);
> >> +     spin_unlock(&hot_func_list_lock);
> >> +
> >> +     return 0;
> >> +}
> >> +EXPORT_SYMBOL_GPL(hot_func_register);
> >> +
> >> +void hot_func_unregister(struct hot_func_type *h)
> >> +{
> >> +     /* unregister */
> >> +     spin_lock(&hot_func_list_lock);
> >> +     list_del_init(&h->list);
> >> +     spin_unlock(&hot_func_list_lock);
> >> +}
> >> +EXPORT_SYMBOL_GPL(hot_func_unregister);
> >> +
> >>  /*
> >>   * Initialize the data structures for hot data tracking.
> >>   */
> >> @@ -714,6 +775,9 @@ int hot_track_init(struct super_block *sb)
> >>       hot_inode_tree_init(root);
> >>       hot_map_array_init(root);
> >>
> >> +     /* Get hot func type */
> >> +     root->hot_func_type = hot_func_get(sb->s_type->name);
> >> +
> >>       root->update_wq = alloc_workqueue(
> >>               "hot_update_wq", WQ_NON_REENTRANT, 0);
> >>       if (!root->update_wq) {
> >> diff --git a/include/linux/hot_tracking.h b/include/linux/hot_tracking.h
> >> index 2ee0d02..3941052 100644
> >> --- a/include/linux/hot_tracking.h
> >> +++ b/include/linux/hot_tracking.h
> >> @@ -23,6 +23,8 @@
> >>  #define HEAT_MAP_BITS 8
> >>  #define HEAT_MAP_SIZE (1 << HEAT_MAP_BITS)
> >>
> >> +#define HOT_NAME_MAX 16
> >> +
> >>  /*
> >>   * A frequency data struct holds values that are used to
> >>   * determine temperature of files and file ranges. These structs
> >> @@ -73,6 +75,25 @@ struct hot_range_item {
> >>       u32 len; /* length in bytes */
> >>  };
> >>
> >> +typedef u64 (hot_rw_freq_calc_fn) (struct timespec old_atime,
> >> +                     struct timespec cur_time, u64 old_avg);
> >> +typedef u32 (hot_temp_calc_fn) (struct hot_freq_data *freq_data);
> >> +typedef bool (hot_is_obsolete_fn) (struct hot_freq_data *freq_data);
> >> +
> >> +struct hot_func_ops {
> >> +     hot_rw_freq_calc_fn *hot_rw_freq_calc_fn;
> >> +     hot_temp_calc_fn *hot_temp_calc_fn;
> >> +     hot_is_obsolete_fn *hot_is_obsolete_fn;
> >> +};
> >> +
> >> +/* identifies an hot func type */
> >> +struct hot_func_type {
> >> +     char hot_func_name[HOT_NAME_MAX];
> >> +     /* fields provided by specific FS */
> >> +     struct hot_func_ops ops;
> >> +     struct list_head list;
> >> +};
> >> +
> >>  struct hot_info {
> >>       struct radix_tree_root hot_inode_tree;
> >>       spinlock_t lock; /*protect inode tree */
> >> @@ -85,6 +106,7 @@ struct hot_info {
> >>
> >>       struct workqueue_struct *update_wq;
> >>       struct delayed_work update_work;
> >> +     struct hot_func_type *hot_func_type;
> >>  };
> >>
> >>  extern void __init hot_cache_init(void);
> >> @@ -93,4 +115,7 @@ extern void hot_track_exit(struct super_block *sb);
> >>  extern void hot_update_freqs(struct inode *inode, u64 start,
> >>                               u64 len, int rw);
> >>
> >> +extern int hot_func_register(struct hot_func_type *h);
> >> +extern void hot_func_unregister(struct hot_func_type *h);
> >> +
> >>  #endif  /* _LINUX_HOTTRACK_H */
> >> --
> >> 1.7.6.5
> >>
> >> --
> >> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> >> the body of a message to majordomo@...r.kernel.org
> >> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 
> 
> 
> -- 
> Regards,
> 
> Zhi Yong Wu
> --
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