[scudo] Change region size from 1 MB to 2 MB in tests

[Chia-hungDuan]

Summary

In SizeClassAllocator64, the RegionBeg is determined by RegionBase +
random offset. The offset is n pages, where n is a random number less or
equal to 16. However, on certain platforms which have large page size,
it may end up immediately OOM without mapping any block pages. For
example,

PageSize = 64 KB, RegionSize = 1 MB

Suppose the random number n is 16, then the random offset will be
64 * 16 = 1024 KB which is equal to the RegionSize.

On most platforms we don't have such large page size and we have
different PRNG(pseudo random number generator) behaviors, thus we didn't
hit any failures before. Given that this now only affects the tests,
only increase the region size is enough.

Will revisit the logic of calculating the random offset.

[Chia-hungDuan]

Add more contexts to this. After landing D133897, the BatchClass started bumping into the problem on PPC and BatchClass is the most important size class so that it's allocation failure will result in a different test failure. Given that D133897 doesn't change the logic of calculating the random offset, I can only guess that the impact comes from the implementation of pseudo random number generator. Somehow D133897 was reverted. To get it back, we need to ensure the BatchClass won't OOM in these tests.

compiler-rt/lib/scudo/standalone/tests/combined_test.cpp

struct DeathSizeClassConfig {
   static const scudo::uptr MinSizeLog = 10;
   static const scudo::uptr MidSizeLog = 10;
   static const scudo::uptr MaxSizeLog = 13;
   static const scudo::u16 MaxNumCachedHint = 4;
   static const scudo::uptr MaxBytesCachedLog = 12;
   static const scudo::uptr SizeDelta = 0;
 };
 
-static const scudo::uptr DeathRegionSizeLog = 20U;
+static const scudo::uptr DeathRegionSizeLog = 21U;
 struct DeathConfig {
   static const bool MaySupportMemoryTagging = false;
 
   // Tiny allocator, its Primary only serves chunks of four sizes.
   using SizeClassMap = scudo::FixedSizeClassMap<DeathSizeClassConfig>;
   typedef scudo::SizeClassAllocator64<DeathConfig> Primary;
   static const scudo::uptr PrimaryRegionSizeLog = DeathRegionSizeLog;
   static const scudo::s32 PrimaryMinReleaseToOsIntervalMs = INT32_MIN;

compiler-rt/lib/scudo/standalone/tests/primary_test.cpp

SCUDO_TYPED_TEST(ScudoPrimaryTest, BasicPrimary) {
   Allocator->releaseToOS();
   scudo::ScopedString Str;
   Allocator->getStats(&Str);
   Str.output();
 }
 
 struct SmallRegionsConfig {
   using SizeClassMap = scudo::DefaultSizeClassMap;
-  static const scudo::uptr PrimaryRegionSizeLog = 20U;
+  static const scudo::uptr PrimaryRegionSizeLog = 21U;
   static const scudo::s32 PrimaryMinReleaseToOsIntervalMs = INT32_MIN;
   static const scudo::s32 PrimaryMaxReleaseToOsIntervalMs = INT32_MAX;
   static const bool MaySupportMemoryTagging = false;
   typedef scudo::uptr PrimaryCompactPtrT;
   static const scudo::uptr PrimaryCompactPtrScale = 0;
   static const bool PrimaryEnableRandomOffset = true;
   static const scudo::uptr PrimaryMapSizeIncrement = 1UL << 18;
 };