Re: Kernel SCM saga..

H. Peter Anvin
2005-04-08T07:50:26Z

Daniel Phillips wrote:
> On Friday 08 April 2005 03:05, Rogan Dawes wrote:
>
>>Take a look at
>>http://www.linuxshowcase.org/2001/full_papers/ezolt/ezolt_html/
>>
>>Abstract
>>
>>GNU libc's default setting for malloc can cause a significant
>>performance penalty for applications that use it extensively, such as
>>Compaq's high performance extended math library, CXML. The default
>>malloc tuning can cause a significant number of minor page faults, and
>>result in application performance of only half of the true potential.
>
>
> This does not smell like an n*2 suckage, more like n^something suckage.
> Finding the elephant under the rug should not be hard. Profile?
>

Lack of hysteresis can do that, with large swats of memory constantly
being claimed and returned to the system. One way to implement
hysteresis would be based on a decaying peak-based threshold;
unfortunately for optimal performance that requires the C runtime to
have a notion of time, and in extreme cases even be able to do
asynchronous deallocation, but in reality one can probably assume that
the rate of malloc/free is roughly constant over time.

-hpa