consistent_coloring

Description

Starting with the Solaris 2.6 release, the ability to use different page placement policies on the UltraSPARC (sun4u) platform was introduced. A page placement policy attempts to allocate physical page addresses to maximize the use of the L2 cache. Whatever algorithm is chosen as the default algorithm, that algorithm can potentially provide less optimal results than another algorithm for a particular application set. This variable changes the placement algorithm selected for all processes on the system.

Based on the size of the L2 cache, memory is divided into bins. The page placement code allocates a page from a bin when a page fault first occurs on an unmapped page. The page chosen depends on which of the three possible algorithms are used:

• Page coloring - Various bits of the virtual address are used to determine the bin from which the page is selected. This is the default algorithm in the Solaris 8 release. consistent_coloring is set to zero to use this algorithm. No per-process history exists for this algorithm.

• Virtual addr=physical address - Consecutive pages in the program selects pages from consecutive bins. consistent_coloring is set to 1 to use this algorithm. No per-process history exists for this algorithm.

• Bin-hopping - Consecutive pages in the program generally allocate pages from every other bin, but the algorithm occasionally skips more bins. consistent_coloring is set to 2 to use this algorithm. Each process starts at a randomly selected bin and a per-process memory of the last bin allocated is kept.

Dynamic?

Yes

Validation

None. Values larger than 2 cause a number of WARNING: AS_2_BIN: bad consistent coloring value messages to appear on the console and the system hangs immediately thereafter. A power-cycle is required to recover.

When to Change

When the primary workload of the system is a set of long-running high-performance computing (HPC) application(s). Changing this value might provide better performance. File servers, database servers, and systems with a number of active processes (for example, compile or time-sharing servers) will not benefit from changes.

Commitment Level

Unstable