RFR (S) 8213587 - Speed up CDS dump time by using resizable hashtables
Ioi Lam
ioi.lam at oracle.com
Mon Nov 19 03:50:11 UTC 2018
On 11/17/18 10:28 PM, Jiangli Zhou wrote:
> Hi Ioi,
>
> On 11/17/18 6:48 PM, Ioi Lam wrote:
>
>>
>>
>> On 11/17/18 1:54 PM, Jiangli Zhou wrote:
>>> Hi Ioi,
>>>
>>> This looks good. Glad to see the change that utilizes the existing
>>> BasicHashtable. Thanks Coleen for the suggestion!
>>>
>>> To avoid changing the existing assumptions about BasicHashtable and
>>> Hashtable, how about adding a destructor to the new KVHashtable
>>> instead of BasicHashtable? Just did a quick test, which seems to
>>> work properly.
>>>
>> Hi Jiangli,
>>
>> Thanks for the review.
>>
>> Not freeing the entries when a BasicHashtable is destructed is a bug.
>> None of the existing BasicHashtables (and subclasses thereof) are
>> ever destructed, so I don't think my code would impact them. Also, if
>> any code depends on the entries not freed even if the table is
>> destructed, that's clearly a bug in that code, and it should be fixed.
>>
>> If I don't add the destructor to BasicHashtable, the next person who
>> wants to allocate/free BasicHashtables will run in to the same issue.
>
> Dictionary, PackageEntryTable, ModuleEntryTable and G1CodeRootSetTable
> are derived from Hashtable and they call free_buckets() in their
> destructors. So free_buckets() will be called twice when those tables
> are freed although it's harmless. If you want to avoid the duplicated
> call, you could remove the free_buckets() calls from those classes'
> destructors and keep the current BasicHashtables changes. I don't have
> a strong opinion on this, I'll leave it to you to decide.
>
>
Hi Jiangli,
Good catch. I've remove the call to free_buckets() in the destructor of
those 4 classes. Here's the delta from the last webrev:
http://cr.openjdk.java.net/~iklam/jdk12/8213587-resize-cds-hashtables.v04-delta/
Also, I found 2 problems while doing this. Hashtables in HotSpot are
really a mess.
https://bugs.openjdk.java.net/browse/JDK-8214029
https://bugs.openjdk.java.net/browse/JDK-8214030
Thanks
- Ioi
> Thanks,
>
> Jiangli
>>
>> Thanks
>> - Ioi
>>
>>
>>> Thanks,
>>>
>>> Jiangli
>>>
>>>
>>> On 11/16/18 7:55 PM, Ioi Lam wrote:
>>>> Hi Coleen,
>>>>
>>>> I deleted the default value for MEMFLAGS as you suggested. For my
>>>> instantiated templates, I still use mtInternal, though, since I
>>>> can't find anything better for using at CDS dump time.
>>>>
>>>> Also, Jiangli noted that there's a memory leak, because I allocate
>>>> and free the KVHashtable dynamically. So I added a destructor to
>>>> BasicHashtable to free the buckets and the block-allocated entries.
>>>>
>>>> http://cr.openjdk.java.net/~iklam/jdk12/8213587-resize-cds-hashtables.v03/
>>>>
>>>>
>>>> http://cr.openjdk.java.net/~iklam/jdk12/8213587-resize-cds-hashtables.v03-delta/
>>>>
>>>>
>>>> This comment around Hashtable::allocate_new_entry() is wrong now --
>>>> "The allocator in blocks is preferable but doesn't have free
>>>> semantics". Maybe I should change it to this?
>>>>
>>>> "The block allocator in BasicHashtable has less fragmentation, but
>>>> the memory is not freed until the whole table is freed. Use
>>>> allocate_new_entry() if you want to immediately free the memory
>>>> used by each entry".
>>>>
>>>> I am rerunning hs-tiers{1,2,3,4} to catch any issues. I also tested
>>>> the solaris/x64 build since it seems to break every time you do
>>>> something with templates :-(
>>>>
>>>> Thanks!
>>>> - Ioi
>>>>
>>>> On 11/16/18 1:36 PM, coleen.phillimore at oracle.com wrote:
>>>>>
>>>>> Hi Ioi, I really like this new wrapper on the old hashtable to
>>>>> not have to write the boilerplate code!
>>>>>
>>>>> http://cr.openjdk.java.net/~iklam/jdk12/8213587-resize-cds-hashtables.v02/src/hotspot/share/utilities/hashtable.hpp.udiff.html
>>>>>
>>>>>
>>>>> + MEMFLAGS F = mtInternal,
>>>>>
>>>>>
>>>>> I think you should require the mt type though and not make it a
>>>>> default parameter. mtInternal is not very useful to finding memory
>>>>> leaks.
>>>>>
>>>>> Apart from this (which I don't need to see another version), your
>>>>> change looks good and nice to get good performance benefits from
>>>>> this.
>>>>>
>>>>> thanks,
>>>>> Coleen
>>>>>
>>>>> On 11/15/18 12:31 AM, Ioi Lam wrote:
>>>>>> Coleen pointed out to me off-line that the good old (and ugly)
>>>>>> BasicHashtable already supports resizing. I think that might be a
>>>>>> better starting point for this RFE:
>>>>>>
>>>>>> http://cr.openjdk.java.net/~iklam/jdk12/8213587-resize-cds-hashtables.v02/
>>>>>>
>>>>>>
>>>>>> I wrote a new template class called "KVHashtable" (copying the
>>>>>> style from ResourceHashtable). That way, you can instantiate
>>>>>> different (Key -> Value) mappings without writing tons of
>>>>>> boilerplate code. The performance is similar to my previous
>>>>>> version, and the code is much cleaner.
>>>>>>
>>>>>> I also renamed the RFE title, as well as the subject line of this
>>>>>> RFR e-mail.
>>>>>>
>>>>>> Thanks
>>>>>>
>>>>>> - Ioi
>>>>>>
>>>>>>
>>>>>> On 11/14/18 5:14 PM, Jiangli Zhou wrote:
>>>>>>> Hi Ioi,
>>>>>>>
>>>>>>> On 11/14/18 9:09 AM, Ioi Lam wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On 11/13/18 4:05 PM, Jiangli Zhou wrote:
>>>>>>>>> Hi Ioi,
>>>>>>>>>
>>>>>>>>> The change looks reasonable to me in general. It would be
>>>>>>>>> helpful to see the performance difference with the expendable
>>>>>>>>> table. Do you have any data when large number of classes are
>>>>>>>>> loaded (>20000)? How much saving does it provide?
>>>>>>>>>
>>>>>>>>
>>>>>>>> Hi Jiangli, thanks for the review. For dumping 30292 classes:
>>>>>>>>
>>>>>>>> BEFORE: 93.971 sec
>>>>>>>> AFTER: 34.761 sec
>>>>>>>
>>>>>>> Thanks for the data! That's about 2.6x improvement with large
>>>>>>> set of classes.
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Jiangli
>>>>>>>>
>>>>>>>> Thanks
>>>>>>>> - Ioi
>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>>
>>>>>>>>> Jiangli
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 11/8/18 10:35 PM, Ioi Lam wrote:
>>>>>>>>>> https://bugs.openjdk.java.net/browse/JDK-8213587
>>>>>>>>>> http://cr.openjdk.java.net/~iklam/jdk12/8213587-configurable-resource-hash.v01/
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> TL;DR: -- add a subclass to ResourceHashtable to allow the
>>>>>>>>>> table size to be
>>>>>>>>>> dynamically specified when the table is constructed.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> *** C++ template guru alert ***
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> I don't know much about C++ templates, so my attempt on doing
>>>>>>>>>> this may be
>>>>>>>>>> ill-advised.
>>>>>>>>>>
>>>>>>>>>> I *think* that with my patch, the performance of existing
>>>>>>>>>> code, which uses
>>>>>>>>>> a statically-defined SIZE, should not be affected, as the
>>>>>>>>>> C++ compiler
>>>>>>>>>> should be able to constant-propagate and reduce the new code:
>>>>>>>>>>
>>>>>>>>>> ALWAYSINLINE unsigned size() const {
>>>>>>>>>> if (SIZE != CONFIGURABLE_SIZE) {
>>>>>>>>>> return SIZE;
>>>>>>>>>> } else {
>>>>>>>>>> return _configured_table_size;
>>>>>>>>>> }
>>>>>>>>>> }
>>>>>>>>>>
>>>>>>>>>> ALWAYSINLINE Node** get_table() const {
>>>>>>>>>> if (SIZE != CONFIGURABLE_SIZE) {
>>>>>>>>>> return (Node**)(&_static_table[0]);
>>>>>>>>>> } else {
>>>>>>>>>> return _configured_table;
>>>>>>>>>> }
>>>>>>>>>> }
>>>>>>>>>>
>>>>>>>>>> Node** lookup_node(unsigned hash, K const& key) {
>>>>>>>>>> unsigned index = hash % size(); <-----
>>>>>>>>>> Node** table = get_table();
>>>>>>>>>> Node** ptr = &table[index]; <-----
>>>>>>>>>>
>>>>>>>>>> back to the old code:
>>>>>>>>>>
>>>>>>>>>> Node** lookup_node(unsigned hash, K const& key) {
>>>>>>>>>> unsigned index = hash % SIZE; <-----
>>>>>>>>>> Node** ptr = &_table[index]; <-----
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> If anyone has a better way of doing this, I'd love to hear it!
>>>>>>>>>>
>>>>>>>>>> Thanks!
>>>>>>>>>> - Ioi
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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