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Hugetlbfs pages are dynamically allocate-able

Hugetlbfs pages are dynamically allocate-able

Posted Jan 20, 2011 17:12 UTC (Thu) by emunson (subscriber, #44357)
Parent article: Transparent huge pages in 2.6.38

Your description of using huge pages via hugetlbfs is not quite correct. Most modern kernels and architectures support dynamically allocating huge pages after boot.


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Hugetlbfs pages are dynamically allocate-able

Posted Jan 21, 2011 6:38 UTC (Fri) by Tuna-Fish (guest, #61751) [Link]

Only if there is contiguous real memory available. Under real-world situations, there rarely is.

Just try allocating space on hugetlbfs after running an active web server for a few hours.

Hugetlbfs pages are dynamically allocate-able

Posted Jan 21, 2011 9:31 UTC (Fri) by jthill (subscriber, #56558) [Link]

I think the memory compaction patch is intended to fix that:

Mel ran some simple tests showing that, with compaction enabled, he was able to allocate over 90% of the system's memory as huge pages while simultaneously decreasing the amount of reclaim activity needed.

Hugetlbfs pages are dynamically allocate-able

Posted Jan 21, 2011 15:35 UTC (Fri) by emunson (subscriber, #44357) [Link]

The presence of contiguous memory will be entirely dependant on the system and work load. You are correct that allocating huge pages becomes more difficult as memory is fragmented. My reply was to the section of the article that said hugetlbfs based huge pages must be set aside at boot time which is not correct for all page sizes. On systems that support them, 1GB and 16GB pages must be reserved at boot, but 2MB, 4MB, and 16MB pages can be allocated any time there is contiguous space.


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