superpages not solving "PV entries" limit warning
Charles Owens
cowens at greatbaysoftware.com
Thu May 10 18:33:18 UTC 2012
On 5/10/12 12:37 PM, Alan Cox wrote:
> On Thu, May 10, 2012 at 10:52 AM, Charles Owens
> <cowens at greatbaysoftware.com <mailto:cowens at greatbaysoftware.com>> wrote:
>
> That's very helpful! I had read about that and wondered if it
> applied to i386.
>
> Should I have expected "superpages" to completely cure the
> condition... or does it just help? Should I now be looking at
> tuning the related pmap sysctls to give further relief?
>
>
> Superpages won't cure the problem due to the nature of your workload.
> After a fork, writes to portions of the address space that are both
> superpages and copy-on-write will trigger demotion, or
> re-instantiation of the 4KB page granularity PV entries. Ultimately,
> repromotion to superpages may occur, but in the meantime, your peak
> usage of PV entries is only slightly reduced.
>
> The bottom line is that you'll need to resort to tuning.
>
> Alan
Ok. Very good.
Lastly, since we're talking about this (for the future) -- is enabling
of superpages generally recommended for amd64?
Thanks,
Charles
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