Re: [LSF/MM/BPF TOPIC] Memory fragmentation with large block sizes

[Christoph Hellwig <hch@infradead.org>]

Hannes,

can you share your results on the mailing list?

On Thu, Feb 19, 2026 at 10:54:48AM +0100, Hannes Reinecke wrote:
> Hi all,
> 
> I (together with the Czech Technical University) did some experiments trying
> to measure memory fragmentation with large block sizes.
> Testbed used was an nvme setup talking to a nvmet storage over
> the network.
> 
> Doing so raised some challenges:
> 
> - How do you _generate_ memory fragmentation? The MM subsystem is
>   precisely geared up to avoid it, so you would need to come up
>   with some idea how to defeat it. With the help from Willy I managed
>   to come up with something, but I really would like to discuss
>   what would be the best option here.
> - What is acceptable memory fragmentation? Are we good enough if the
>   measured fragmentation does not grow during the test runs?
> - Do we have better visibility into memory fragmentation other than
>   just reading /proc/buddyinfo?
> 
> And, of course, I would like to present (and discuss) the results
> of the testruns done on 4k, 8k, and 16k blocksizes.
> 
> Not sure if this should be a storage or MM topic; I'll let the
> lsf-pc decide.
> 
> Cheers,
> 
> Hannes
> -- 
> Dr. Hannes Reinecke                  Kernel Storage Architect
> hare@suse.de                                +49 911 74053 688
> SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
> HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich
> 
> 
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