Re: [RFC PATCH 0/4] Enable >0 order folio memory compaction

[Luis Chamberlain <mcgrof@kernel.org>]

On Wed, Sep 20, 2023 at 07:05:25PM -0700, John Hubbard wrote:
> On 9/20/23 18:16, Luis Chamberlain wrote:
> > On Wed, Sep 20, 2023 at 05:55:51PM -0700, Luis Chamberlain wrote:
> > > Are there other known recipes test help test this stuff?
> > 
> > You know, it got me wondering... since how memory fragmented a system
> > might be by just running fstests, because, well, we already have
> > that automated in kdevops and it also has LBS support for all the
> > different large block sizes on 4k sector size. So if we just had a
> > way to "measure" or "quantify" memory fragmentation with a score,
> > we could just tally up how we did after 4 hours of testing for each
> > block size with a set of memory on the guest / target node / cloud
> > system.
> > 
> >    Luis
> 
> I thought about it, and here is one possible way to quantify
> fragmentation with just a single number. Take this with some
> skepticism because it is a first draft sort of thing:
> 
> a) Let BLOCKS be the number of 4KB pages (or more generally, then number
> of smallest sized objects allowed) in the area.
> 
> b) Let FRAGS be the number of free *or* allocated chunks (no need to
> consider the size of each, as that is automatically taken into
> consideration).
> 
> Then:
>       fragmentation percentage = (FRAGS / BLOCKS) * 100%
> 
> This has some nice properties. For one thing, it's easy to calculate.
> For another, it can discern between these cases:
> 
> Assume a 12-page area:
> 
> Case 1) 6 pages allocated allocated unevenly:
> 
> 1 page allocated | 1 page free | 1 page allocated | 5 pages free | 4 pages allocated
> 
> fragmentation = (5 FRAGS / 12 BLOCKS) * 100% = 41.7%
> 
> Case 2) 6 pages allocated evenly: every other page is allocated:
> 
> fragmentation = (12 FRAGS / 12 BLOCKS) * 100% = 100%

Thanks! Will try this!

BTW stress-ng might also be a nice way to do other pathalogical things here.

  Luis