On Thu, Sep 27, 2012 at 02:23:16PM +0800, Zhi Yong Wu wrote: > On Thu, Sep 27, 2012 at 11:43 AM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > On Sun, Sep 23, 2012 at 08:56:30PM +0800, zwu.kernel@xxxxxxxxx wrote: > >> From: Zhi Yong Wu <wuzhy@xxxxxxxxxxxxxxxxxx> > >> > >> 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. > > > > So, let me see if I've got the relationship straight: > > > > - sb->s_hot_info.hot_inode_tree indexes hot_inode_items, one per inode > > > > - hot_inode_item contains access frequency data for that inode > > > > - hot_inode_item holds a heat hash node to index the access > > frequency data for that inode > > > > - hot_inode_item.hot_range_tree indexes hot_range_items for that inode > > > > - hot_range_item contains access frequency data for that range > > > > - hot_range_item holds a heat hash node to index the access > > frequency data for that range > > > > - sb->s_hot_info.heat_inode_hl indexes per-inode heat hash nodes > > > > - sb->s_hot_info.heat_range_hl indexes per-range heat hash nodes > Correct. > > > > How about some ascii art? :) Just looking at the hot inode item case > > (the range item case is the same pattern, though), we have: > > > > > > heat_inode_hl hot_inode_tree > > | | > > | V > > | +-------hot_inode_item-------+ > > +---+ | frequency data | > > | V ^ V > > | ...<--hot_inode_item-->... | ...<--hot_inode_item-->.... > > | frequency data | frequency data > > | ^ | ^ > > | | | | > > | | | | > > +------>hot_hash_node-->hot_hash_node-->hot_hash_node-->.... > Great, can we put them in hot_tracking.txt in Documentation? > > > > > > There's no actual data stored in the hot_hash_node, just pointer > > back to the frequency data, a hlist_node and a pointer to the > > hashlist head. IOWs, I agree with Ram that this does not need to > > exist and just embedding a hlist_node inside the hot_inode_item is > > all that is needed. i.e: > > > > heat_inode_hl hot_inode_tree > > | | > > | V > > | +-------hot_inode_item-------+ > > | | frequency data | > > +---+ | hlist_node | > > | V ^ | V > > | ...<--hot_inode_item-->... | | ...<--hot_inode_item-->.... > > | frequency data | | frequency data > > +------>hlist_node-----------+ +------->hlist_node--->..... > > > > There's no need for separate allocations, initialisations, locks and > > reference counting - all that is already in the hot_inode_item. The > > items have the same lifecycle limitations - a hot_hash_node must be > > torn down before the frequency data it points to is freed. Finally, > > there's no difference in how you move it between lists. > How will you know if one hot_inode_item should be moved between lists > when its freq data is changed? Record the current temperature in the frequency data, and if it changes, change the list it is on. > > Indeed, calling it a hash is wrong - there's not hashing at all > > - it keeping an array of list where each entry corresponds to a > > specific temperature. It is a *heat map*, not a hash list. i.e. > > inode_heat_map, not heat_inode_hl. HEAT_MAP_SIZE, not HASH_SIZE. > OK. > > > > As it is, there aren't any users of the heat maps that are generated > > in this patch set - it's not even exported to userspace or to > > debugfs, so I'm not sure how it will be used yet. How are these heat > > maps going to be used by filesystems, Zhi? > In hot_hash_calc_temperature(), you can see that one hot_inode or > hot_range's freq data will be distilled into one temperature value, > then it will be inserted to the heat map based on its temperature. > When the file corresponding to the inode or range got hotter or cold, > its location will be changed in the heat map based on its new > temperature in hot_hash_update_hash_table(). Yes, but a hot_inode_item or hot_range_item can only have one location in the heat map, right? So it doesn't need external structure to point to the frequency data to track this.... > And the user will retrieve those freq data and temperature info via > debugfs or ioctl interfaces. Right - but that data is only extracted after an initial hot_inode_tree lookup - The heat map itself is never directly used for lookups. If it's not used for lookups based on temperature, why is it needed? Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
