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Transparent Page Sharing is not utilized under normal workloads on Nehalem based Xeon 5500 series CPUs (1020524)

Symptoms

Within the ESX or ESXi 4.x host the values for SHRD and SHRDSVD that are an indication of Transparent Page Sharing (TPS) usage are very low or shows as not being utilized under normal workloads on Nehalem based Xeon 5500 series CPUs or other platforms that support hwMMU (EPT / RVI).

This can incorrectly indicate that Nehalem hardware running ESX/ESXi 4.x is not fully utilizing this feature.

Resolution

On Nehalem based systems with Hardware assisted Memory Management Unit (MMU), performance improves from 10 - 20% by using large pages.

Since TPS is done per small page, the VMkernel delays page sharing until host memory becomes over-committed. In the background, the ESX host gathers information about TPS, then uses it when it needs more memory.

TPS is only used when the host is over-committed on Nehalem based systems.

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