Architectural Support for Optimizing Huge Page Selection Within the OS

Irregular, memory-intensive applications often incur high translation lookaside bu!er (TLB) miss rates that result in signi"cant address translation overheads. Employing huge pages is an e!ective way to reduce these overheads, however in real systems the number of available huge pages can be limited when system memory is nearly full and/or fragmented. Thus, huge pages must be used selectively to back application memory. This work demonstrates that choosing memory regions that incur the most TLB misses for huge page promotion best reduces address translation overheads. We call these regions High reUse TLB-sensitive data (HUBs). Unlike prior work which relies on expensive per-page software counters to identify promotion regions, we propose new architectural support to identify these regions dynamically at application runtime.

We propose a promotion candidate cache (PCC) that identi"es HUB candidates based on hardware page table walks after a lastlevel TLB miss. This small, "xed-size structure tracks huge pagealigned regions (consisting of 𝐿 base pages), ranks them based on observed page table walk frequency, and only keeps the most frequently accessed ones. Evaluated on applications of various memory intensity, our approach successfully identi"es application pages incurring the highest address translation overheads. Our approach demonstrates that with the help of a PCC, the OS only needs to promote 4% of the application footprint to achieve more than 75% of the peak achievable performance, yielding 1.19-1.33→ speedups over 4KB base pages alone. In real systems where memory is typically fragmented, the PCC outperforms Linux's page promotion policy by 14% (when 50% of total memory is fragmented) and 16% (when 90% of total memory is fragmented) respectively.