> From: Christopher Schultz [mailto:ch...@christopherschultz.net] > Subject: Re: Problem with CATALINA_OPTS in setenv.sh > > "With the -XX:+AlwaysPreTouch option the JVM touches every single > > byte of the max heap size with a '0', resulting in the memory being > > allocated in the physical memory in addition to being reserved in > > the internal data structure (virtual memory). Pretouching is single > > threaded, so it is expected behavior that it causes JVM startup to > > be delayed. The trade off is that it will reduce page access time > > later, as the pages will already be loaded into memory."
> Sounds like garbage to me. The OS isn't going to keep pages in RAM > just because they are zeroed. Also, unless the JVM does it exactly > correctly (which it probably *is* doing), the zeroing-operation might > actually be a no-op. Definitely not a no-op - it will cause the guest OS to allocate what it thinks are real pages, create VMAs, and do all sorts of other bookkeeping that is pointless in a VM environment. The hypervisor has the last word here, and it will happily swap pages that the guest OS thinks are in pseudo-real memory. That's why the pre-touch option is useless in anything other than a dedicated bare-metal system. > > The fact that Tomcat is crashing during the pre-touch would > > indicate that you can't actually use a 2 GiB heap on a supposed 4 > > GiB VM - something other than the heap is eating up a lot of space. > > You should probably remove the option and reduce the heap size. > But the process isn't failing on pre-touch. It's failing when it's > trying to bind a socket to a port. Doing the bind requires additional non-heap process and kernel memory; I suspect this puts it over the limit imposed by either the guest OS or hypervisor. - Chuck THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY MATERIAL and is thus for use only by the intended recipient. If you received this in error, please contact the sender and delete the e-mail and its attachments from all computers. -----Original Message----- The most likely result from using AlwaysPreTouch is that you get more memory pressure and therefore more swapping to virtual memory. I can't really see a use-case for this option. I'm guessing your dev requested this because #security or #sawitonstackoverflow. Given that it crashes your JVM, I'd say you have a decent argument for NOT using this option even if it fails the sniff test for other reasons. - -chris -----BEGIN PGP SIGNATURE----- Comment: GPGTools - http://gpgtools.org Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQIzBAEBCAAdFiEEMmKgYcQvxMe7tcJcHPApP6U8pFgFAltjWTQACgkQHPApP6U8 pFgRlBAAl6yo/nyrV7NnaCXMz34b+6OLqpPjTiR5Rm06YoGuoZD5CDpiDgwMR59O qJmKn6545gtF/CjbjOLdtJCeHH+hMzEKy2JcEfBIkc0pen5jK+AQmFVMl7xpfx+/ qjD08IWALpqAuKTPEZQNUVCAOIVPjOdLuk9wsOXtyTa8TBAoy50nVk9h+O72+Zpr z25ynggKA/wDzs49NoHaN0x8o8+Y40IJr02dQ9O4QGh+Jt3OT7QxJMDuu7OvFNko E/Y8PsUeiENSGxVtprw7HbBYhLYQJ8aD3fCk9munDlnyzWhf5ASy5nnRncQfhMsP XyI8pJKvV+qZNveBIj4jBwO81vjRzUGyUeYwmSPmZq6dFU4ZhNktFEi/iCTy2seb S36rvGQg16/ekBZtNhqJDdIbeImbjggVK8dwPTqv5FoMx1w8XQB57vh1ROhPo7u2 9esbImd262rdQuE9feAfrY6hi0t9iU40rrCzFntvFm+TpcNyouOgXX7fFIXnVWz8 oGRRYOGFOreSLHjHLn4Nptl220o0Ux8n1iZ7mZDMJSPueidov95YExrYFKawUxwc kZJi/gEfZfcd3YpxLcH3O6I2vTJmvGPYgIIBIfBR0gSqgGhN9ad87rVoEqM+AE8D TCsdOSDS7A+PqU50Efwqspp1Xae9z2SXSg5e66kGjKQiJ0oua6A= =Nn19 -----END PGP SIGNATURE----- --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
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