The buffer pool's device tier (detiler scratch buffers and the staging
shadows of written guest buffers) retained at most 512 MiB by default.
A title whose working set of these buffers is larger allocates and
frees device memory continually: PPSA14632 (LEGO Horizon Adventures)
had 70761 misses and 69828 evictions per 10 s with 485 of 512 MiB
retained, each a vkAllocateMemory or vkFreeMemory.
The default budget is now an eighth of the largest device-local heap,
and at least the old 512 MiB, so a 16 GiB card retains up to 2 GiB and
an 8 GiB card 1 GiB. APS5_STAGING_POOL_MIB still sets it.
Only the constructor knows the device, so only the budget comes from the
heap. Whether the tier is in use at all (APS5_STAGING_POOL_MIB unset or
not 0) stays a static check, DeviceTierEnabled, which Capacity, Usage and
tierFor share, so the size classes and the tier stay consistent.
On PPSA14632 with 2 GiB the device tier has 1312 misses and 99
evictions per 10 s (1628 MiB retained), and presents rise from about 34
to about 39 per 10 s.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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