Re: [PATCH/RFC] Shared page tables

From: Brian Twichell
Date: Tue Jan 24 2006 - 23:19:18 EST


Brian Twichell wrote:


We evaluated page table sharing on x86_64 and ppc64 setups, using a database
OLTP workload. In both cases, 4-way systems with 64 GB of memory were used.

On the x86_64 setup, page table sharing provided a 25% increase in performance,
when the database buffers were in small (4 KB) pages. In this case, over 14 GB
of memory was freed, that had previously been taken up by page tables. In the
case that the database buffers were in huge (2 MB) pages, page table sharing
provided a 4% increase in performance.

Our ppc64 experiments used an earlier version of Dave's patch, along with
ppc64-specific code for sharing of ppc64 segments. On this setup, page
table sharing provided a 49% increase in performance, when the database
buffers were in small (4 KB) pages. Over 10 GB of memory was freed, that
had previously been taken up by page tables. In the case that the database
buffers were in huge (16 MB) pages, page table sharing provided a 3% increase
in performance.

Hi,

Just wanted to dispel any notion that may be out there that
the improvements we've seen are peculiar to an IBM product
stack.

The 49% improvement observed using small pages on ppc64 used
Oracle as the DBMS. The other results used DB2 as the DBMS.

So, the improvements not peculiar to an IBM product stack,
and moreover the largest improvement was seen with a non-IBM
DBMS.

Note, the relative improvement observed on each platform/pagesize
combination cannot be used to infer relative performance between
DBMS's or platforms.

Cheers,
Brian

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