Re: remap the .text segment into huge pages at run time

Hi,

On 2023-06-14 12:40:18 +0700, John Naylor wrote:
> On Sat, Nov 5, 2022 at 3:27 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> > /*
> > * Make huge pages out of it. Requires at least linux 6.1. We
> could
> > * fall back to MADV_HUGEPAGE if it fails, but it doesn't do all
> that
> > * much in older kernels.
> > */
> > #define MADV_COLLAPSE 25
> > r = madvise(addr, advlen, MADV_COLLAPSE);
> > if (r != 0)
> > fprintf(stderr, "MADV_COLLAPSE failed: %m\n");
> >
> >
> > A real version would have to open /proc/self/maps and do this for at least
> > postgres' r-xp mapping. We could do it for libraries too, if they're
> suitably
> > aligned (both in memory and on-disk).
>
> Hi Andres, my kernel has been new enough for a while now, and since TLBs
> and context switches came up in the thread on... threads, I'm swapping this
> back in my head.

Cool - I think we have some real potential for substantial wins around this.

> For the postmaster, it should be simple to have a function that just takes
> the address of itself, then parses /proc/self/maps to find the boundaries
> within which it lies. I haven't thought about libraries much. Though with
> just the postmaster it seems that would give us the biggest bang for the
> buck?

I think that is the main bit, yes. We could just try to do this for the
libraries, but accept failure to do so?

Greetings,

Andres Freund