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Date:	Wed, 7 Nov 2012 16:27:05 +0800
From:	Zhi Yong Wu <zwu.kernel@...il.com>
To:	"Darrick J. Wong" <darrick.wong@...cle.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 03/19] vfs: add I/O frequency update function

On Wed, Nov 7, 2012 at 6:45 AM, Darrick J. Wong <darrick.wong@...cle.com> wrote:
> On Mon, Oct 29, 2012 at 12:30:45PM +0800, zwu.kernel@...il.com wrote:
>> From: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
>>
>>   Add some util helpers to update access frequencies
>> for one file or its range.
>>
>> Signed-off-by: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
>> ---
>>  fs/hot_tracking.c            |  179 ++++++++++++++++++++++++++++++++++++++++++
>>  fs/hot_tracking.h            |    7 ++
>>  include/linux/hot_tracking.h |    2 +
>>  3 files changed, 188 insertions(+), 0 deletions(-)
>>
>> diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
>> index 68591f0..0a7d9a3 100644
>> --- a/fs/hot_tracking.c
>> +++ b/fs/hot_tracking.c
>> @@ -172,6 +172,137 @@ static void hot_inode_tree_exit(struct hot_info *root)
>>       }
>>  }
>>
>> +struct hot_inode_item
>> +*hot_inode_item_find(struct hot_info *root, u64 ino)
>> +{
>> +     struct hot_inode_item *he;
>> +     int ret;
>> +
>> +again:
>> +     spin_lock(&root->lock);
>> +     he = radix_tree_lookup(&root->hot_inode_tree, ino);
>> +     if (he) {
>> +             kref_get(&he->hot_inode.refs);
>> +             spin_unlock(&root->lock);
>> +             return he;
>> +     }
>> +     spin_unlock(&root->lock);
>> +
>> +     he = kmem_cache_zalloc(hot_inode_item_cachep,
>> +                             GFP_KERNEL | GFP_NOFS);
>> +     if (!he)
>> +             return ERR_PTR(-ENOMEM);
>> +
>> +     hot_inode_item_init(he, ino, &root->hot_inode_tree);
>> +
>> +     ret = radix_tree_preload(GFP_NOFS & ~__GFP_HIGHMEM);
>> +     if (ret) {
>> +             kmem_cache_free(hot_inode_item_cachep, he);
>> +             return ERR_PTR(ret);
>> +     }
>> +
>> +     spin_lock(&root->lock);
>> +     ret = radix_tree_insert(&root->hot_inode_tree, ino, he);
>> +     if (ret == -EEXIST) {
>> +             kmem_cache_free(hot_inode_item_cachep, he);
>> +             spin_unlock(&root->lock);
>> +             radix_tree_preload_end();
>> +             goto again;
>> +     }
>> +     spin_unlock(&root->lock);
>> +     radix_tree_preload_end();
>> +
>> +     kref_get(&he->hot_inode.refs);
>> +     return he;
>> +}
>> +EXPORT_SYMBOL_GPL(hot_inode_item_find);
>> +
>> +static struct hot_range_item
>> +*hot_range_item_find(struct hot_inode_item *he,
>> +                     u32 start)
>> +{
>> +     struct hot_range_item *hr;
>> +     int ret;
>> +
>> +again:
>> +     spin_lock(&he->lock);
>> +     hr = radix_tree_lookup(&he->hot_range_tree, start);
>> +     if (hr) {
>> +             kref_get(&hr->hot_range.refs);
>> +             spin_unlock(&he->lock);
>> +             return hr;
>> +     }
>> +     spin_unlock(&he->lock);
>> +
>> +     hr = kmem_cache_zalloc(hot_range_item_cachep,
>> +                             GFP_KERNEL | GFP_NOFS);
>> +     if (!hr)
>> +             return ERR_PTR(-ENOMEM);
>> +
>> +     hot_range_item_init(hr, start, he);
>> +
>> +     ret = radix_tree_preload(GFP_NOFS & ~__GFP_HIGHMEM);
>> +     if (ret) {
>> +             kmem_cache_free(hot_range_item_cachep, hr);
>> +             return ERR_PTR(ret);
>> +     }
>> +
>> +     spin_lock(&he->lock);
>> +     ret = radix_tree_insert(&he->hot_range_tree, start, hr);
>> +     if (ret == -EEXIST) {
>> +             kmem_cache_free(hot_range_item_cachep, hr);
>> +             spin_unlock(&he->lock);
>> +             radix_tree_preload_end();
>> +             goto again;
>> +     }
>> +     spin_unlock(&he->lock);
>> +     radix_tree_preload_end();
>> +
>> +     kref_get(&hr->hot_range.refs);
>> +     return hr;
>> +}
>> +
>> +/*
>> + * This function does the actual work of updating
>> + * the frequency numbers, whatever they turn out to be.
>> + */
>> +static u64 hot_average_update(struct timespec old_atime,
>> +             struct timespec cur_time, u64 old_avg)
>> +{
>> +     struct timespec delta_ts;
>> +     u64 new_avg;
>> +     u64 new_delta;
>> +
>> +     delta_ts = timespec_sub(cur_time, old_atime);
>> +     new_delta = timespec_to_ns(&delta_ts) >> FREQ_POWER;
>> +
>> +     new_avg = (old_avg << FREQ_POWER) - old_avg + new_delta;
>> +     new_avg = new_avg >> FREQ_POWER;
>> +
>> +     return new_avg;
>> +}
>> +
>> +static void hot_freq_data_update(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->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->last_read_time,
>> +                             cur_time,
>> +                             freq_data->avg_delta_reads);
>
> I think you could just pass in a pointer to
> freq_data->avg_delta_{writes,reads} here...
why?
>
>> +             freq_data->last_read_time = cur_time;
>> +     }
>> +}
>> +
>>  /*
>>   * Initialize kmem cache for hot_inode_item and hot_range_item.
>>   */
>> @@ -199,6 +330,54 @@ err:
>>  EXPORT_SYMBOL_GPL(hot_cache_init);
>>
>>  /*
>> + * Main function to update access frequency from read/writepage(s) hooks
>> + */
>> +void hot_update_freqs(struct inode *inode, u64 start,
>> +                     u64 len, int rw)
>> +{
>> +     struct hot_info *root = inode->i_sb->s_hot_root;
>> +     struct hot_inode_item *he;
>> +     struct hot_range_item *hr;
>> +     u32 cur, end;
>> +
>> +     if (!root || (len == 0))
>> +             return;
>> +
>> +     he = hot_inode_item_find(root, inode->i_ino);
>> +     if (IS_ERR(he)) {
>> +             WARN_ON(1);
>> +             return;
>> +     }
>> +
>> +     spin_lock(&he->hot_inode.lock);
>> +     hot_freq_data_update(&he->hot_inode.hot_freq_data, rw);
>> +     spin_unlock(&he->hot_inode.lock);
>> +
>> +     /*
>> +      * Align ranges on RANGE_SIZE boundary
>> +      * to prevent proliferation of range structs
>> +      */
>> +     end = (start + len + RANGE_SIZE - 1) >> RANGE_BITS;
>> +     for (cur = (start >> RANGE_BITS); cur < end; cur++) {
>
> Hm... start is u64, cur is u32, RANGE_BITS is 20.  Doesn't this overflow if,
> say, I have a sparse file with blocks way out at 2^53 bytes?
ah, good catch, thanks.
>
> Also, RANGE_SIZE means that the hot tracking range granularity is 1MiB?  How
yes.
> did you decide on that?  Will we ever want to change that?
It is one assumption, do you think 1 MB is not appropriate? Do you
mean to add one proc file interface for it?
>
>> +             hr = hot_range_item_find(he, cur);
>> +             if (IS_ERR(hr)) {
>> +                     WARN_ON(1);
>
> WARN(1, "hot_range_item_find returns %d\n", PTR_ERR(hr)); ?
OK, done.
>
> --D
>
>> +                     hot_inode_item_put(he);
>> +                     return;
>> +             }
>> +
>> +             spin_lock(&hr->hot_range.lock);
>> +             hot_freq_data_update(&hr->hot_range.hot_freq_data, rw);
>> +             spin_unlock(&hr->hot_range.lock);
>> +
>> +             hot_range_item_put(hr);
>> +     }
>> +
>> +     hot_inode_item_put(he);
>> +}
>> +EXPORT_SYMBOL_GPL(hot_update_freqs);
>> +
>> +/*
>>   * Initialize the data structures for hot data tracking.
>>   */
>>  int hot_track_init(struct super_block *sb)
>> diff --git a/fs/hot_tracking.h b/fs/hot_tracking.h
>> index e7ba121..cc4666e 100644
>> --- a/fs/hot_tracking.h
>> +++ b/fs/hot_tracking.h
>> @@ -20,6 +20,13 @@
>>  #define FREQ_DATA_TYPE_INODE (1 << 0)
>>  #define FREQ_DATA_TYPE_RANGE (1 << 1)
>>
>> +/* size of sub-file ranges */
>> +#define RANGE_BITS 20
>> +#define RANGE_SIZE (1 << RANGE_BITS)
>> +
>> +#define FREQ_POWER 4
>> +
>>  void hot_inode_item_put(struct hot_inode_item *he);
>> +struct hot_inode_item *hot_inode_item_find(struct hot_info *root, u64 ino);
>>
>>  #endif /* __HOT_TRACKING__ */
>> diff --git a/include/linux/hot_tracking.h b/include/linux/hot_tracking.h
>> index 4233207..e2d6028 100644
>> --- a/include/linux/hot_tracking.h
>> +++ b/include/linux/hot_tracking.h
>> @@ -71,5 +71,7 @@ struct hot_info {
>>  extern void __init hot_cache_init(void);
>>  extern int hot_track_init(struct super_block *sb);
>>  extern void hot_track_exit(struct super_block *sb);
>> +extern void hot_update_freqs(struct inode *inode, u64 start,
>> +                             u64 len, int rw);
>>
>>  #endif  /* _LINUX_HOTTRACK_H */
>> --
>> 1.7.6.5
>>
>> --
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-- 
Regards,

Zhi Yong Wu
--
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