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Date:   Wed, 20 Sep 2023 20:14:26 -0700
From:   Luis Chamberlain <mcgrof@kernel.org>
To:     John Hubbard <jhubbard@nvidia.com>
Cc:     Zi Yan <ziy@nvidia.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Ryan Roberts <ryan.roberts@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        David Hildenbrand <david@redhat.com>,
        "Yin, Fengwei" <fengwei.yin@intel.com>,
        Yu Zhao <yuzhao@google.com>, Vlastimil Babka <vbabka@suse.cz>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Kemeng Shi <shikemeng@huaweicloud.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Rohan Puri <rohan.puri15@gmail.com>,
        Adam Manzanares <a.manzanares@samsung.com>
Subject: Re: [RFC PATCH 0/4] Enable >0 order folio memory compaction
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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