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

[Jay Patel <jaypatel@linux.ibm.com>]

On Mon, 2023-06-19 at 12:25 +0900, Hyeonggon Yoo wrote:
> 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?
Hi Hyeonggon,

Thank you for your response. I acknowledge your feedback,
and I have made the necessary modifications to the patch. I am pleased
to inform you that I have sent the updated version [1], which addresses
the issues we discussed.

[1] 
https://lore.kernel.org/linux-mm/20230628095740.589893-1-jaypatel@linux.ibm.com/T/#u

Thanks,
Jay Patel
> 
> > 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,
>