The New Costs of Physical Memory Fragmentation

DIMES Workshop Best Paper Award
The New Costs of Physical Memory Fragmentation

Alexander Halbuer, Illia Ostapyshyn, Lukas Steiner, Lars Wrenger, Matthias Jung, Christian Dietrich, Daniel LohmannProceedings of the 2nd Workshop on Disruptive Memory SystemsAssociation for Computing Machinery2024Best Paper Award.
PDF Details 10.1145/3698783.3699378 [BibTex]

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BibTex Entry

@inproceedings{halbuer:24:dimes,
author = {Alexander Halbuer and Illia Ostapyshyn and Lukas Steiner and Lars Wrenger and Matthias Jung and Christian Dietrich and Daniel Lohmann},
booktitle = {Proceedings of the 2nd Workshop on Disruptive Memory Systems},
doi = {10.1145/3698783.3699378},
entrysubtype = {Workshop},
location = {Austin, Texas, USA},
publisher = {Association for Computing Machinery},
title = {The New Costs of Physical Memory Fragmentation},
year = {2024},
}

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Abstract

External fragmentation is becoming a serious problem again after paging temporarily solved it with its one-size-fits-all 4 KiB approach. The increasing adoption of mixed base, huge, and giant page sizes, DRAM energy-saving techniques, and memory disaggregation, necessitates a memory management system capable of handling larger entities in the range of multiple megabytes up to several gigabytes.

A case study in Linux reveals that the operating system reasonably minimizes fragmentation up to huge page size, but falls short when it comes to larger granularities. Therefore, it requires much effort to entirely free a memory block for powering down or returning it to the memory provider; in some cases, this may be entirely impossible due to immovable kernel memory.

Additionally, our analysis highlights that the page cache is responsible for a large share of memory usage, as it keeps all cached pages until memory pressure rises. This behavior originates from the outdated assumption that utilizing memory comes at no cost and, therefore, requires further investigation.