Re: Posix Shared Mem patch

On Fri, Jun 29, 2012 at 2:52 PM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> Hi All,
>
> In a *very* quick patch I tested using huge pages/MAP_HUGETLB for the mmap'ed
> memory.
> That gives around 9.5% performance benefit in a read-only pgbench run (-n -S -
> j 64 -c 64 -T 10 -M prepared, scale 200, 6GB s_b, 8 cores, 24GB mem).
>
> It also saves a bunch of memory per process due to the smaller page table
> (shared_buffers 6GB):
> cat /proc/$pid_of_pg_backend/status |grep VmPTE
> VmPTE:      6252 kB
> vs
> VmPTE:        60 kB
>
> Additionally it has the advantage that top/ps/... output under linux now looks
> like:
>  PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+  COMMAND
> 10603 andres    20   0 6381m 4924 1952 R    21  0.0   0:28.04 postgres
>
> i.e. RES now actually shows something usable... Which is rather nice imo.
>
> I don't have the time atm into making this something useable, maybe somebody
> else want to pick it up? Looks pretty worthwile investing some time.
>
> Because of the required setup we sure cannot make this the default but...

... those results are just spectacular (IMO). nice!

merlin