RFR(S): 7069863: G1: SIGSEGV running SPECjbb2011 and -UseBiasedLocking
vladimir.kozlov at oracle.com
Wed Jul 27 19:06:27 UTC 2011
// When compressed oops are used the preferred heap base is calculated
// by subtracting the requested size from the 32Gb boundary and using
// the result as the base address for heap reservation. If the size is
// not aligned to HeapRegion::GrainBytes passed into the ReservedHeapSpace
// constructor then the base of the actual reserved heap may end up
// differing from the requested base address. If this happens then we
// could end up using a non-optimal compressed oops mode.
213 // prefix_align == suffix_align).
^ prefix_align < suffix_align
ReservedSpace::ReservedSpace() also misses the call to
failed_to_reserve_as_requested() after the code which handle wrong alignment.
Add assert into ReservedSpace::initialize()
// Assert that if noaccess_prefix is used, it is the same as alignment.
assert(noaccess_prefix == 0 ||
noaccess_prefix == alignment, "noaccess prefix wrong");
Why we have next code? Should we do this alignment adjustment at the beginning
of the method?
355 _alignment = MAX2(alignment, (size_t) os::vm_page_size());
John Cuthbertson wrote:
> Hi Everyone,
> Can I have a couple of volunteers look over these changes - the webrev
> can be found at: http://cr.openjdk.java.net/~johnc/7069863/webrev.0/
> The issue was caused by an implicit null check in generated code not
> firing. The implicit null check did not trap as a result of a mismatch
> between the compressed oops mode and the calculated heap base. Also the
> page below heap base was not being protected. The mismatch between the
> compressed oops mode and heap base was the result of the G1 heap
> initialization code passing in a total heap size (G1 heap and perm) that
> was not a multiple of the alignment passed into the ReservedSpace
> constructor. Hence the preferred heap base address was not correctly
> aligned causing the ReservedSpace to be allocated at an address other
> than the preferred heap base. The page below the heap base was not
> protected because the G1 heap initialization code was calling the wrong
> ReservedSpace constructor.
> Testing: the failing test case; various small tests with various
> collectors, large heaps, and +PrintCompressedOopsMode.
> Many thanks to Vladimir and Igor for helping to diagnose the issue.
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