Re: [RFC PATCH ] mm/slub: Reducing slub memory wastage

[Hyeonggon Yoo <42.hyeyoo@gmail.com>]

On Tue, Jun 13, 2023 at 06:25:48PM +0530, Jay Patel wrote:
> > <...snip...> 
> > > I conducted tests on systems with 160 CPUs and 16 CPUs, using  4K
> > > and
> > > 64K page sizes. Through these tests, it was observed that the patch
> > > successfully reduces the wastage of slab memory without any
> > > noticeable
> > > performance degradation in the hackbench test report. However, it
> > > should
> > > be noted that the patch also increases the total number of objects,
> > > leading to an overall increase in total slab memory usage.
> > 
> > <...snip...>
> > 
> > Then my question is that, why is this a useful change if total memory
> > usage is increased?
> > 
> This patch aimed in reducing memory wastage can potentially lead to an
> increase in the slab order for a slab cache. Consequently, this
> increase in page order can result in a higher number of objects per
> slab, reducing wastage and leading to a more efficient utilization of
> memory.


if you define utilization as percentage of memory that is
being used out of total memory, utilization becomes worse... (based
on data you provided)

I think 'less memory wastage' is a useful feature only if the total
memory usage is reduced so that it could be used for other purposes.

I mean, if it consumes more memory on a same workload (in most cases),
who would like it?

> This enhancement is advantageous since the presence of unused
> objects can be leveraged in the future, depending on varying
> workloads. 

At least we need to know when it is leveraged and what kinds of workloads
would benefit...

Thanks,

-- 
Hyeonggon Yoo
Undergraduate | Chungnam National University