Re: [PATCH] SLUB: Do not fallback to mininum order if __GFP_NORETRY is set

[Christopher Lameter]

On Sat, 21 Apr 2018, Vlastimil Babka wrote:

> > The problem is that SLUB does not honor GFP_NORETRY. The semantics of
> > GFP_NORETRY are not followed.
>
> The caller might want SLUB to try hard to get that high-order page that
> will minimize memory waste (e.g. 2MB page for 3 640k objects), and
> __GFP_NORETRY will kill the effort on allocating that high-order page.

Well yes since *_NORETRY says that fallbacks are acceptable.

> Thus, using __GPF_NORETRY for "please give me a space-optimized object,
> or nothing (because I have a fallback that's better than wasting memory,
> e.g. by using 1MB page for 640kb object)" is not ideal.
>
> Maybe __GFP_RETRY_MAYFAIL is a better fit? Or perhaps indicate this
> situation to SLUB with e.g. __GFP_COMP, although that's rather ugly?

Yuck. None of that sounds like an intuitive approach.