[Nix-dev] Transparent Hugepage Support & Redis

[Tobias Geerinckx-Rice]

Hullo,

On 12/06/16 12:00, 4levels wrote:
> when starting Redis I keep getting warnings about Transparent Hugepage
> Support being enabled in the kernel and how this may negatively impact
> Redis' performance.
> [snip]
>  3. Or is there a better way to only disable this for Redis only?
>     My guess would be something like "always [madvise redis] never"

The whole point of HUGEPAGE_MADVISE as I understand it, is that
hugepages are not allocated until an application explicitly requests
them using MADV_HUGEPAGE. In other words: the *Transparent* Hugepage
Support that Redis warns about is in fact disabled by default.

So unless Redis explicitly requests hugepages only to then complain
about them, or there's some other weird interaction, my first guess
would be that their check is a bit too strict and assumes that !never ==
always.

If the warning really bothers you, you can always override your kernel
configuration with something like:

      // Copy-pasted from my config, sort of:
      nixpkgs.config.packageOverrides = {
        stdenv = stdenv // {
          platform = stdenv.platform // {
            kernelExtraConfig = ''
              TRANSPARENT_HUGEPAGE? n
            '';
          };
        };
      };

but my suspicion that it's entirely unneeded still stands.

Kind regards,

T G-R