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Comment by pca006132 | Hacker News Reader

Just wondering, how useful is it to get code and stack memory into hugepages? I thought you usually access them sequentially so it doesn't matter that much to put them in hugepages.

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Code is not really accessed sequentially. Just imagine a function calling another function which sits in another translation unit. Depending what the linker is going to do but there's a good chance that these won't sit near to each other unless you explicitly optimized for that case. This is why source-code level locality is also important - to minimize the instruction cache misses. And also why you don't want to go mad about making everything dynamically dispatched in the code unless you really need to (e.g. virtual functions).

EDIT: Putting the code segment into hugepages will relief some of the pressure of VADDR translation which is otherwise larger with 4K segments. Whether this will impact the runtime execution time positively or stay neutral I think it greatly depends on the workload and cannot be said upfront.

Wrt code, look at the bench in the article. Even with sequential access, you can get a decent speedup using huge pages. But unless you have a good profile and using PGO, it'll likely not be that sequential for code. Like everything else you'll need to measure it to know exactly what benefit you might get. As a starting point, you can start at looking at the itlb load misses with perf stat -d

Stack access is another story as it's usually local and sequential so it might not be that useful.

The most benefit comes from the fact that you end up with a lot less TLB misses, since single mapping covers a large chunk of memory. Predictable memory access pattern helps with caches misses thanks to hardware prefetch, but as far as I know hardware prefetch won't work if it would cause TLB miss on most CPUs.

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