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

On Sat, Nov 5, 2022 at 3:27 PM Andres Freund <andres@anarazel.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.

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?

--
John Naylor
EDB: http://www.enterprisedb.com