RFR(L): 8064457: Introduce compressed oops mode "disjoint base" and improve compressed heap handling.
Coleen Phillimore
coleen.phillimore at oracle.com
Wed Dec 10 19:25:10 UTC 2014
Goetz,
Also, our 32 bit platforms don't like:
1 * SIZE_64K * SIZE_32G,
2 * SIZE_64K * SIZE_32G,
3 * SIZE_64K * SIZE_32G,
4 * SIZE_64K * SIZE_32G,
16 * SIZE_64K * SIZE_32G,
32 * SIZE_64K * SIZE_32G,
34 * SIZE_64K * SIZE_32G,
0
I think it's probably fine to ifdef them.
Coleen
On 12/10/14, 2:22 PM, Coleen Phillimore wrote:
>
> Hi Goetz,
>
> I have some initial comments, which are much less detailed than
> Vladimir's comments. I haven't actually processed all the
> implementation details yet.
>
> I think get_attach_addresses_for_disjoint_mode function belongs in
> virtualspace.cpp and not in universe. I like that the compressed oop
> reservation logic is moved to virtualspace.cpp. I think this is an
> improvement over the Universe::preferred_heap_base() logic which was
> also difficult.
>
> The Hotspot coding style doesn't dictate 80 columns anymore (there is
> debate whether it should have or not, which we try not to have this
> debate), but I found the very long lines in this code inconsistent
> with other Hotspot code. I had to expand my window to cover my whole
> screen. Can you reduce some to at least 100?
>
> For example, I aligned these parameters to see better since there are
> so many (the indentation isn't right in email).
>
> void ReservedHeapSpace::try_reserve_range(char *const highest_start,
> char *lowest_start,
> size_t attach_point_alignment,
> char *aligned_HBMA, //
> HeapBaseMinAddress
> char *upper_bound,
> size_t size,
> size_t alignment,
> bool large) {
>
> Why is highest_start not const char* ? Doesn't char* const
> highest_start just restrict you from changing the pointer and not what
> it points to? This seems odd to do.
>
> The control flow in initialize_compressed_heap makes no sense to me.
> It seems like there should be an exit when the best allocation for
> compression is achieved. But it falls through after
> try_reserve_range(). I can't figure out why it should fall through....
>
> I was expecting something like:
>
> if (PrintCompressedOopsMode && Verbose) {
> tty->print(" == H E A P B A S E M I N A D D R E S S ==\n");
> }
> get the heap at aligned HeapBaseMinAddress, return if success...
>
> if (PrintCompressedOopsMode && Verbose) {
> tty->print(" == U N S C A L E D ==\n");
> }
> try to get heap base for unscaled access, return if successful
>
> etc.
>
>
> You should make this into a little function for each return and for
> the end of the initialize function, or move it to the
> ReservedHeapSpace constructor (caller).
>
> assert(_base == NULL ||
> markOopDesc::encode_pointer_as_mark(_base)->decode_pointer() == _base,
> "area must be distinguishable from marks for mark-sweep");
> assert(_base == NULL ||
> markOopDesc::encode_pointer_as_mark(&_base[size])->decode_pointer() ==
> &_base[size],
> "area must be distinguishable from marks for mark-sweep");
> }
>
> I ran this through JPRT and this line didn't compile on macos:
>
> const uint64_t num_attempts_to_try = MIN2(HeapSearchSteps,
> num_attempts_possible);
>
> I'm retrying now as:
>
> const uint64_t num_attempts_to_try =
> MIN2((uint64_t)HeapSearchSteps, num_attempts_possible);
>
> Sorry for the delay looking at this. This is a big change that I
> needed to make more time to read. I am pleased that it's a
> performance improvement.
>
> Thanks,
> Coleen
>
> On 12/8/14, 10:54 AM, Lindenmaier, Goetz wrote:
>> Hi,
>>
>> This is just a ping to gc/rt mailing lists to reach appropriate
>> people.
>>
>> I please need a reviewer from gc or rt, could somebody have a
>> look at this?
>>
>> Short summary:
>> - new cOops mode disjointbase that allows optimizations on PPC
>> improving over heapbased
>> - search for heaps: finds zerobased on sparc Solaris 11 and Aix
>> - concentrate cOops heap allocation code in one function
>> http://cr.openjdk.java.net/~goetz/webrevs/8064457-disjoint/webrev.02/
>>
>> Please reply only to the original thread in hotspot-dev to keep this
>> local.
>>
>> Thanks and best regards,
>> Goetz.
>>
>> -----Original Message-----
>> From: Vladimir Kozlov [mailto:vladimir.kozlov at oracle.com]
>> Sent: Donnerstag, 4. Dezember 2014 19:44
>> To: Lindenmaier, Goetz
>> Cc: 'hotspot-dev developers'
>> Subject: Re: RFR(L): 8064457: Introduce compressed oops mode
>> "disjoint base" and improve compressed heap handling.
>>
>> This looks good to me.
>>
>> Now we need second review since changes are significant. Preferable from
>> GC group since you changed ReservedHeapSpace. They will be affected
>> most. Review from Runtime is also welcome.
>>
>> Thanks,
>> Vladimir
>>
>> On 12/4/14 10:27 AM, Lindenmaier, Goetz wrote:
>>> Hi Vladimir.
>>>
>>> Sorry. I updated the webrev once more. Hope it's fine now.
>>> At least I can write comments :)
>>>
>>> Best regards,
>>> Goetz
>>>
>>> -----Original Message-----
>>> From: Vladimir Kozlov [mailto:vladimir.kozlov at oracle.com]
>>> Sent: Thursday, December 04, 2014 5:54 PM
>>> To: Lindenmaier, Goetz
>>> Cc: 'hotspot-dev developers'
>>> Subject: Re: RFR(L): 8064457: Introduce compressed oops mode
>>> "disjoint base" and improve compressed heap handling.
>>>
>>> I spotted an other bug.
>>> You replaced !_base with _base != NULL when moved code to
>>> try_reserve_range() - it should be _base == NULL.
>>> The same problem in asserts:
>>>
>>> + assert(_base != NULL ||
>>> markOopDesc::encode_pointer_as_mark(_base)->decode_pointer() == _base,
>>> + "area must be distinguishable from marks for mark-sweep");
>>> + assert(_base != NULL ||
>>> markOopDesc::encode_pointer_as_mark(&_base[size])->decode_pointer()
>>> == &_base[size],
>>> + "area must be distinguishable from marks for mark-sweep");
>>>
>>>
>>> Also you did not remove _base && in next place:
>>>
>>> + (_base && _base + size > zerobased_max))) { // Unscaled
>>> delivered an arbitrary address.
>>>
>>> New comment is good.
>>>
>>> Thanks,
>>> Vladimri
>>>
>>> On 12/4/14 1:45 AM, Lindenmaier, Goetz wrote:
>>>> Hi Vladimir,
>>>>
>>>>> Add more extending comment explaining that.
>>>> The comment for try_reserve_heap was meant to explain that.
>>>> I further added a comment in initialize_compressed_heap().
>>>>
>>>>> You need another parameter to pass UnscaledOopHeapMax or
>>>>> zerobased_max.
>>>> Oh, thanks a lot! That's important. Fixed.
>>>>
>>>>> I mean that you already checked _base == NULL so on other side of
>>>>> || _base != NULL - why you need (_base &&) check?
>>>> Sorry, now I got it. Removed.
>>>>
>>>> I updated the webrev:
>>>> http://cr.openjdk.java.net/~goetz/webrevs/8064457-disjoint/webrev.02/
>>>> Increment on top of the increment :)
>>>> http://cr.openjdk.java.net/~goetz/webrevs/8064457-disjoint/webrev.02/incremental_diffs2.patch
>>>>
>>>>
>>>> Thanks,
>>>> Goetz.
>>>>
>>>>
>>>> -----Original Message-----
>>>> From: Vladimir Kozlov [mailto:vladimir.kozlov at oracle.com]
>>>> Sent: Mittwoch, 3. Dezember 2014 18:32
>>>> To: Lindenmaier, Goetz; 'hotspot-dev at openjdk.java.net'
>>>> Subject: Re: RFR(L): 8064457: Introduce compressed oops mode
>>>> "disjoint base" and improve compressed heap handling.
>>>>
>>>> Comments are below.
>>>>
>>>> On 12/3/14 5:49 AM, Lindenmaier, Goetz wrote:
>>>>> Hi Vladimir,
>>>>>
>>>>> thanks for looking at the change! See my comments inline below.
>>>>>
>>>>> I made a new webrev:
>>>>> http://cr.openjdk.java.net/~goetz/webrevs/8064457-disjoint/webrev.02/
>>>>> Incremental changes:
>>>>> http://cr.openjdk.java.net/~goetz/webrevs/8064457-disjoint/webrev.02/incremental_diffs.patch
>>>>>
>>>>>
>>>>> Best regards,
>>>>> Goetz.
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Vladimir Kozlov [mailto:vladimir.kozlov at oracle.com]
>>>>>> Sent: Mittwoch, 3. Dezember 2014 00:46
>>>>>> To: Lindenmaier, Goetz; 'hotspot-dev at openjdk.java.net'
>>>>>> Subject: Re: RFR(L): 8064457: Introduce compressed oops mode
>>>>>> "disjoint base" and improve compressed heap handling.
>>>>>>
>>>>>> This looks good to me. Someone in runtime/gc have to look on it too.
>>>>>>
>>>>>> universe.cpp about
>>>>>> SystemProperty("com.sap.vm.test.compressedOopsMode"
>>>>>> we have:
>>>>>> java.vm.info=mixed mode, sharing
>>>>>> so we can have:
>>>>>> java.vm.compressedOopsMode=...
>>>>> Yes, that's good for me. Fixed.
>>>>>
>>>>>> I am not expert in properties names but I don't want to have
>>>>>> 'com.sap'
>>>>>> in VM's property name.
>>>>>> virtualspace.cpp:
>>>>>> Could you fix release() - it does not reset _alignment?
>>>>> Fixed.
>>>>>
>>>>>> In try_reserve_heap(), please, use (base == NULL) instead of
>>>>>> (!base).
>>>>>> And you don't need 'return;' in alignment check at the end of
>>>>>> method.
>>>>> Fixed.
>>>>>
>>>>>> In initialize_compressed_heap() again (!_base).
>>>>> Fixed.
>>>>>
>>>>>> You don't stop (check
>>>>>> (base == NULL)) after successful unscaled, zerobased, disjointbase
>>>>>> allocations. You need to separate them with the check:
>>>>>>
>>>>>> +
>>>>>> + }
>>>>>> + }
>>>>>> + if (_base == NULL) {
>>>>>> +
>>>>>> + if (PrintCompressedOopsMode && Verbose) {
>>>>>> + tty->print(" == Z E R O B A S E D ==\n");
>>>>>> + }
>>>>>> and so on.
>>>>> No, I can't and don't want to check for _base != NULL.
>>>>> I always keep the result of the last try, also if it didn't fulfil
>>>>> the required properties.
>>>>> So I take that result and go into the next check. That check
>>>>> might succeed
>>>>> with the heap allocated before.
>>>>> This allows me to separate allocation and placement criteria, and
>>>>> to have the
>>>>> placement criteria checked in only one place (per mode).
>>>>> Only for HeapBaseMinAddress I don't do it that way, I explicitly
>>>>> call release().
>>>>> This way I can enforce mode heapbased.
>>>> I see what you are saying. It was not clear from comments what is
>>>> going on.
>>>> Add more extending comment explaining that.
>>>>
>>>>>> num_attempts calculation and while() loop are similar in unscaled
>>>>>> and
>>>>>> zerobased cases. Could you move it into a separate method?
>>>>> I can do that, but I don't like it as I have to pass in 7 parameters.
>>>> You need an other parameter to pass UnscaledOopHeapMax or
>>>> zerobased_max.
>>>>
>>>>> That makes the code not much more readable. The function will
>>>>> look like this:
>>>> I think initialize_compressed_heap() is more readable now.
>>>>
>>>>> void ReserveHeapSpace::try_reserve_range(char *const
>>>>> highest_start, char *lowest_start, size_t attach_point_alignment,
>>>>> char *aligned_HBMA,
>>>>> size_t size, size_t alignment, bool large) {
>>>>> guarantee(HeapSearchSteps > 0, "Don't set HeapSearchSteps to
>>>>> 0");
>>>>>
>>>>> const size_t attach_range = highest_start - lowest_start;
>>>>> // Cap num_attempts at possible number.
>>>>> // At least one is possible even for 0 sized attach range.
>>>>> const uint64_t num_attempts_possible = (attach_range /
>>>>> attach_point_alignment) + 1;
>>>>> const uint64_t num_attempts_to_try = MIN2(HeapSearchSteps,
>>>>> num_attempts_possible);
>>>>>
>>>>> const size_t stepsize = align_size_up(attach_range /
>>>>> num_attempts_to_try, attach_point_alignment);
>>>>>
>>>>> // Try attach points from top to bottom.
>>>>> char* attach_point = highest_start;
>>>>> while (attach_point >= lowest_start &&
>>>>> attach_point <= highest_start && // Avoid wrap around.
>>>>> (!_base || _base < aligned_HBMA || _base + size >
>>>>> (char *)UnscaledOopHeapMax)) {
>>>>> try_reserve_heap(size, alignment, large, attach_point);
>>>>> attach_point -= stepsize;
>>>>> }
>>>>> }
>>>>>
>>>>>
>>>>>> In disjointbase while() condition no need for _base second check:
>>>>>> + (_base == NULL ||
>>>>>> + ((_base + size > (char *)OopEncodingHeapMax) &&
>>>>> I need this for the same reason as above: This is the check for
>>>>> successful allocation.
>>>> I mean that you already checked _base == NULL so on other side of
>>>> || _base != NULL - why you need (_base &&) check?
>>>>
>>>> Thanks,
>>>> Vladimir
>>>>
>>>>>
>>>>>
>>>>> Thanks,
>>>>> Vladimir
>>>>>
>>>>> On 11/21/14 5:31 AM, Lindenmaier, Goetz wrote:
>>>>>> Hi,
>>>>>>
>>>>>> I prepared a new webrev trying to cover all the issues mentioned
>>>>>> below.
>>>>>> http://cr.openjdk.java.net/~goetz/webrevs/8064457-disjoint/webrev.01/
>>>>>>
>>>>>>
>>>>>> I moved functionality from os.cpp and universe.cpp into
>>>>>> ReservedHeapSpace::initialize_compressed_heap().
>>>>>> This class offers to save _base and _special, which I would have
>>>>>> to reimplement
>>>>>> if I had improved the methods I had added to os.cpp to also
>>>>>> allocate large page
>>>>>> heaps.
>>>>>> Anyways, I think this class is the right place to gather code
>>>>>> trying to reserve
>>>>>> the heap.
>>>>>> Also, I get along without setting the shift, base,
>>>>>> implicit_null_check etc. fields
>>>>>> of Universe, so there is no unnecessary calling back and forth
>>>>>> between the two
>>>>>> classes.
>>>>>> Universe gets the heap back, and then sets the properties it
>>>>>> needs to configure
>>>>>> the compressed oops.
>>>>>> All code handling the noaccess prefix is in a single method, too.
>>>>>>
>>>>>> Best regards,
>>>>>> Goetz.
>>>>>>
>>>>>> Btw, I had to workaround a SS12u1 problem: it wouldn't compile
>>>>>> char * x = (char*)UnscaledOopHeapMax - size in 32-bit mode.
>>>>>>
>>>>>>
>>>>>> -----Original Message-----
>>>>>> From: hotspot-dev [mailto:hotspot-dev-bounces at openjdk.java.net]
>>>>>> On Behalf Of Lindenmaier, Goetz
>>>>>> Sent: Montag, 17. November 2014 09:33
>>>>>> To: 'Vladimir Kozlov'; 'hotspot-dev at openjdk.java.net'
>>>>>> Subject: RE: RFR(L): 8064457: Introduce compressed oops mode
>>>>>> "disjoint base" and improve compressed heap handling.
>>>>>>
>>>>>> Hi Vladimir,
>>>>>>
>>>>>>> It is very significant rewriting and it takes time to evaluate it.
>>>>>> Yes, I know ... and I don't want to push, but nevertheless a ping
>>>>>> can be useful sometimes. Thanks a lot for looking at it.
>>>>>>
>>>>>>> And I would not say it is simpler then before :)
>>>>>> If I fix what you propose it's gonna get even more simple ;)
>>>>>>> These is what I found so far.
>>>>>>> The idea to try to allocate in a range instead of just below
>>>>>>> UnscaledOopHeapMax or OopEncodingHeapMax is good. So I would ask
>>>>>>> to do
>>>>>>> several attempts (3?) on non_PPC64 platforms too.
>>>>>> Set to 3.
>>>>>>
>>>>>>> It is matter of preference but I am not comfortable with switch
>>>>>>> in loop.
>>>>>>> For me sequential 'if (addr == 0)' checks is simpler.
>>>>>> I'll fix this.
>>>>>>
>>>>>>> One thing worries me that you release found space and try to get it
>>>>>>> again with ReservedHeapSpace. Is it possible to add new
>>>>>>> ReservedHeapSpace ctor which simple use already allocated space?
>>>>>> This was to keep diff's small, but I also think a new constructor
>>>>>> is good.
>>>>>> I'll fix this.
>>>>>>
>>>>>>> The next code in ReservedHeapSpace() is hard to understand ():
>>>>>>> (UseCompressedOops && (requested_address == NULL ||
>>>>>> requested_address+size > (char*)OopEncodingHeapMax) ?
>>>>>>> may be move all this into noaccess_prefix_size() and add comments.
>>>>>> I have to redo this anyways if I make new constructors.
>>>>>>
>>>>>>> Why you need prefix when requested_address == NULL?
>>>>>> If we allocate with NULL, we most probably will get a heap where
>>>>>> base != NULL and thus need a noaccess prefix.
>>>>>>
>>>>>>> Remove next comment in universe.cpp:
>>>>>>> // SAPJVM GL 2014-09-22
>>>>>> Removed.
>>>>>>
>>>>>>> Again you will release space so why bother to include space for
>>>>>>> classes?:
>>>>>>> + // For small heaps, save some space for compressed
>>>>>>> class pointer
>>>>>>> + // space so it can be decoded with no base.
>>>>>> This was done like this before. We must assure the upper bound
>>>>>> of the
>>>>>> heap is low enough that the compressed class space still fits in
>>>>>> there.
>>>>>>
>>>>>> virtualspace.cpp
>>>>>>
>>>>>>> With new code size+noaccess_prefix could be requested. But later
>>>>>>> it is
>>>>>>> not used if WIN64_ONLY(&& UseLargePages) and you will have empty
>>>>>>> non-protected page below heap.
>>>>>> There's several points to this:
>>>>>> * Also if not protectable, the heap base has to be below
>>>>>> the real start of the
>>>>>> heap. Else the first object in the heap will be
>>>>>> compressed to 'null'
>>>>>> and decompression will fail.
>>>>>> * If we don't reserve the memory other stuff can end up in
>>>>>> this space. On
>>>>>> errors, if would be quite unexpected to find memory there.
>>>>>> * To get a heap for the new disjoint mode I must control
>>>>>> the size of this.
>>>>>> Requesting a heap starting at (aligned base + prefix)
>>>>>> is more likely to fail.
>>>>>> * The size for the prefix must anyways be considered when
>>>>>> deciding whether the
>>>>>> heap is small enough to run with compressed oops.
>>>>>> So distinguishing the case where we really can omit this would
>>>>>> require
>>>>>> quite some additional checks everywhere, and I thought it's not
>>>>>> worth it.
>>>>>>
>>>>>> matcher.hpp
>>>>>>
>>>>>>> Universe::narrow_oop_use_implicit_null_checks() should be true
>>>>>>> for such
>>>>>>> case too. So you can add new condition with || to existing ones.
>>>>>>> The
>>>>>>> only condition you relax is base != NULL. Right?
>>>>>> Yes, that's how it's intended.
>>>>>>
>>>>>> arguments.* files
>>>>>>
>>>>>>> Why you need PropertyList_add changes.
>>>>>> Oh, the code using it got lost. I commented on this in the
>>>>>> description in the webrev.
>>>>>> "To more efficiently run expensive tests in various compressed
>>>>>> oop modes, we set a property with the mode the VM is running in.
>>>>>> So far it's called "com.sap.vm.test.compressedOopsMode" better
>>>>>> suggestions are welcome (and necessary I guess). Our long running
>>>>>> tests that are supposed to run in a dedicated compressed oop mode
>>>>>> check this property and abort themselves if it's not the expected
>>>>>> mode."
>>>>>> When I know about the heap I do
>>>>>> Arguments::PropertyList_add(new
>>>>>> SystemProperty("com.sap.vm.test.compressedOopsMode",
>>>>>> narrow_oop_mode_to_string(narrow_oop_mode()),
>>>>>> false));
>>>>>> in universe.cpp.
>>>>>> On some OSes it's deterministic which modes work, there we don't
>>>>>> start such tests.
>>>>>> Others, as you mentioned OSX, are very indeterministic. Here we
>>>>>> save testruntime with this.
>>>>>> But it's not that important.
>>>>>> We can still parse the PrintCompresseOopsMode output after the
>>>>>> test and discard the
>>>>>> run.
>>>>>>
>>>>>>> Do you have platform specific changes?
>>>>>> Yes, for ppc and aix. I'll submit them once this is in.
>>>>>>
>>>>>> From your other mail:
>>>>>>> One more thing. You should allow an allocation in the range when
>>>>>>> returned from OS allocated address does not match
>>>>>>> requested address. We had such cases on OSX, for example, when
>>>>>>> OS allocates at different address but still inside range.
>>>>>> Good point. I'll fix that in os::attempt_reserve_memory_in_range.
>>>>>>
>>>>>> I'll ping again once a new webrev is done!
>>>>>>
>>>>>> Best regards,
>>>>>> Goetz.
>>>>>>
>>>>>>
>>>>>> On 11/10/14 6:57 AM, Lindenmaier, Goetz wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> I need to improve a row of things around compressed oops heap
>>>>>>> handling
>>>>>>> to achieve good performance on ppc.
>>>>>>> I prepared a first webrev for review:
>>>>>>> http://cr.openjdk.java.net/~goetz/webrevs/8064457-disjoint/webrev.00/
>>>>>>>
>>>>>>>
>>>>>>> A detailed technical description of the change is in the webrev
>>>>>>> and according bug.
>>>>>>>
>>>>>>> If requested, I will split the change into parts with more
>>>>>>> respective less impact on
>>>>>>> non-ppc platforms.
>>>>>>>
>>>>>>> The change is derived from well-tested code in our VM.
>>>>>>> Originally it was
>>>>>>> crafted to require the least changes of VM coding, I changed it
>>>>>>> to be better
>>>>>>> streamlined with the VM.
>>>>>>> I tested this change to deliver heaps at about the same
>>>>>>> addresses as before.
>>>>>>> Heap addresses mostly differ in lower bits. In some cases
>>>>>>> (Solaris 5.11) a heap
>>>>>>> in a better compressed oops mode is found, though.
>>>>>>> I ran (and adapted) test/runtime/CompressedOops and
>>>>>>> gc/arguments/TestUseCompressedOops*.
>>>>>>>
>>>>>>> Best regards,
>>>>>>> Goetz.
>>>>>>>
>>>>>>>
>
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