[jared_hulbert]

The original blog post title is intentionally clickbaity. You know, to bait people into clicking. Also I do want to challenge people to really think here.

Seeing if the cached file data can be accessed quickly is the point of the experiment. I can't get mmap() to open a file with huge pages.

void* buffer = mmap(NULL, size_bytes, PROT_READ, (MAP_HUGETLB | MAP_HUGE_1GB), fd, 0); doesn't work.

You can can see my code here https://github.com/bitflux-ai/blog_notes. Any ideas?

[mastax]

MAP_HUGETLB can't be used for mmaping files on disk, it can only be used with MAP_ANONYMOUS, with a memfd, or with a file on a hugetlbfs pseudo-filesystem (which is also in memory).

[mananaysiempre]

It looks like there is in theory support for that[1]? But the patches for ext4[2] did not go through.

[1] https://lwn.net/Articles/686690/

[2] https://lwn.net/Articles/718102/

[inetknght]

> MAP_HUGETLB can't be used for mmaping files on disk

False. I've successfully used it to memory-map networked files.

[jandrewrogers]

Read the man pages, there are restrictions on using the huge page option with mmap() that mean it won’t do what you might intuit it will in many cases. Getting reliable huge page mappings is a bit fussy on Linux. It is easier to control in a direct I/O context.