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,
--
John Hubbard
NVIDIA
