httpd: add notes about arenas and object heaps

We don't users being confused if an innocuous-looking
line of code allocates unnexpectedly large values.

1 files changed, 6 insertions, 1 deletions

diff --git a/ext/mwrap/httpd.h b/ext/mwrap/httpd.h
index 17fb187..fe4fe2f 100644
--- a/ext/mwrap/httpd.h
+++ b/ext/mwrap/httpd.h
@@ -600,7 +600,12 @@ static enum mw_qev each_at(struct mw_h1 *h1, struct mw_h1req *h1r)
                                 size, h->as.live.gen, h->real);
         }
         rcu_read_unlock();
-        FPUTS("</table></body></html>", fp);
+        FPUTS("</table><pre>\nNotes:\n"
+"* 16344-byte (64-bit) or 16344-byte (32-bit) allocations in\n"
+"  Ruby &lt;= 3.0 aligned to 0x4000 are likely for object heap slots.\n"
+"* 4080-byte allocations in Perl 5 are likely for arenas\n"
+"  (set via the PERL_ARENA_SIZE compile-time macro)"
+"</pre></body></html>", fp);
         return h1_200(h1, &html, TYPE_HTML);
 }