MGLRU-FG Delivering Up To 10~40% Higher Performance For Linux In Some Tests
Linux's Multi-Gen LRU "MGLRU" has already achieved nice performance gains for Linux in recent years by optimizing page reclaims and improves performance under memory pressure. The new MGLRU-FG patches aim to take things further...
Memory Grouped Least Recently Used (MGLRU) is an eviction policy that has been enhanced to potentially deliver up to 10-40% higher performance for Linux in certain tests. The update introduces a tier-PID protection mechanism for eviction time, while also utilizing access-time frequency to promote pages.
A unified set of helpers, based on the referenced count of a folio, has been introduced. Each access increments the folio's referenced count, stored in folio flags. A logarithmic tier is used to map the reference count, with specific thresholds defined: LRU_REFS_REFERENCED (1), LRU_REFS_WORKINGSET (2), LRU_REFS_PROTECTED (3), and LRU_REFS_MAX (7).
When the referenced count reaches a certain threshold, the folio is promoted proactively, bypassing the need to wait for the PID controller. Additionally, the usage of PG_workingset and PG_referenced has been simplified, with these values now comprising the low two bits of the refs count. This change reduces the bit usage of MGLRU's refs count by one, and improves the accuracy of MGLRU's reference accounting.
The enhancements result in a 10% - 40% higher performance, or lower refault rates, in various tests. Certain workloads exhibit a significantly reduced runtime. The improvement is primarily due to MGLRU's increased ability to distinguish hotter working sets. Tests across multiple servers with different architectures, desktops, and Android have shown promising results.
Compared to the previous version (V2), V3 is more affected by anonymous over-reclaim, but overall, it provides better results. However, this problem should be addressed separately. Despite being a major change to LRU, including modifications to Active/Inactive reading, the new policy is already performing well and is considered usable.
Michael Larabel, the principal author of Phoronix.com, has authored over 20,000 articles about Linux hardware support, performance, graphics drivers, and other topics. He is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org.
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