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Date: Thu, 8 Nov 2012 10:52:51 +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 Thu, Nov 8, 2012 at 2:49 AM, Darrick J. Wong <darrick.wong@...cle.com> wrote:
> On Wed, Nov 07, 2012 at 04:27:05PM +0800, Zhi Yong Wu wrote:
>> 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->avg_delta_{reads,writes} seems to be an in/out parameter, but by
> specifying it once as an in parameter and again as an lvalue, you're increasing
> the chances that someone will screw it up some time later -- you're not
> preventing me from accidentally writing this:
>
> freq_data->avg_delta_writes = hot_average_update(..., freq_data->avg_delta_reads);
>
> ...which (at least in my head) becomes an easier mistake to make once you start
> mixing in the function pointers a few patches later, and (my) brain has to wrap
> itself around all the punctuation.
>
>> >> + 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.
>
> Actually, I should go further -- why not use loff_t? The rest of the fs/ code
> does.
done, 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?
>
> I don't know about a procfs interface -- debugfs, perhaps?
>
> But actually, I was thinking that the fs might have a better idea of the range
> granularity that it wants to handle. Possibly it might be useful to try to
> align with raid stripes or other topology, too... though that's difficult.
>
> Also, for the fses that use allocation units (clusters), it might be useful
> to collect heat data per-cluster.
>
> On the other hand, it might not make much of a difference since most files tend
> to fit in ~4K anyway, and the extra granularity will increase memory
> consumption for large files. I don't mind having a 1MB default, but having a
> knob would certainly make it easier to tune, or in the future, to test if that
> 1MB default still makes sense.
thanks.
>
> --D
>
>> >
>> >> + 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
>> >>
>> >> --
>> >> 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
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-ext4" 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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