Bump default maximum stack size

[xavierleroy]

Now that stack allocation is entirely under the control of the OCaml runtime system, it's time to use more generous stack limits than those provided by operating systems.

This commit sets the default maximum stack size to 128 Miwords, i.e. 1 Gib for 64-bit platforms and 512 Mib for 32-bit platforms.

See #10736 and #10954 for context.

[shindere]

Xavier Leroy (2022/05/04 06:40 -0700):

Now that stack allocation is entirely under the control of the OCaml runtime system, it's time to use more generous stack limits than those provided by operating systems. This commit sets the default maximum stack size to 128 Miwords, i.e. 1 Gib for 64-bit platforms and 512 Mib for 32-bit platforms. See #10736 and #10954 for context. You can view, comment on, or merge this pull request online at: #11238 -- Commit Summary -- * Bump default maximum stack size -- File Changes -- M runtime/caml/config.h (3) -- Patch Links -- https://github.com/ocaml/ocaml/pull/11238.patch https://github.com/ocaml/ocaml/pull/11238.diff

How about documenting in which unit the stack size is expressed? I assume it's in words but it could be helpful to write it explicitly in the comment to make it easier to grasp why a constant size yields different sizes on different platforms. Also, I'm sorry, I didn't understand what you did in the test. You sem to specify a constant size, still you say that it's to make the test robust to increases of the stack size. Would you mind clarifying?

[xavierleroy]

How about documenting in which unit the stack size is expressed? I assume it's in words

The unit is indeed words, and it's documented in the reference manual where the OCAMLRUNPARAM variable is documented, as well as in the runtime/caml/config.h source file. What extra documentation is needed?

Also, I'm sorry, I didn't understand what you did in the test. You sem
to specify a constant size, still you say that it's to make the test
robust to increases of the stack size. Would you mind clarifying?

The test wants to trigger a stack overflow. After increasing the default max stack size, it would no longer trigger it. Hence the test must be run with a fixed max stack size that is known to trigger the stack overflow.

[shindere]

Xavier Leroy (2022/05/10 05:37 -0700):

> How about documenting in which unit the stack size is expressed? I assume it's in words The unit is indeed words, and it's documented in the reference manual where the OCAMLRUNPARAM variable is documented, as well as in the `runtime/caml/config.h` source file. What extra documentation is needed?

My bad, I missed the "(words)" bit. Sorry.

> Also, I'm sorry, I didn't understand what you did in the test. You sem > to specify a constant size, still you say that it's to make the test > robust to increases of the stack size. Would you mind clarifying? The test wants to trigger a stack overflow.

Yes.

After increasing the default max stack size, it would no longer trigger it. Hence the test must be run with a fixed max stack size that is known to trigger the stack overflow.

Yes yes. I misunderstood that you were emphasizing the fact that it's *fixed* wihch matters, but of course what matters is that it's larger than the max size.

[shindere]

@xavierleroy don't you want to add a Changes entry?

To please check-typo but also because that may be interesting to users.

[xavierleroy]

Changes entry added, now merging !