On 04/09/13 07:52, Rob Landley wrote: > On 04/05/2013 02:53:12 PM, Byron Stanoszek wrote: >> Rob, >> >> FWIW I have a patch to do something like this. It even gives you a rdsize=xxx >> tunable kernel parameter that lets you specify the size of the tmpfs, which >> acts like the -osize= mount flag (so phrases like 100M or 20% works). So >> doing >> things like 'cat /dev/zero > filename' will not run you out of all available >> memory. (Note: If you don't specify rdsize= on the kernel command line, it >> will >> not convert rootfs to tmpfs). > > In init/do_mounts.c the boot infrastructure already has kernel command line > options "rootflags=" and "rootfstype=", so the logical thing to do is > probably to hook those up to rootfs. (That way instead of special casing a > new option we use the existing tmpfs option parsing.) > > The default tmpfs size is 50%, which solves the "trivial to exhaust memory > and panic a kernel running under rootfs" problem. Having one tmpfs also fixes > the case that multiple tmpfs mounts (for /home and /var, for example,) have > separate memory limits that don't coordinate with each other, so if /home can > use 30% and /var can use 30%, that's 60% plus whatever rootfs is already > using, so you can easily squeeze the kernel against the wall without meaning > to. (Yes, you can make one tmpfs mount and --bind mount from there to > elsewhere, I've seen that done. Having rootfs just _be_ tmpfs makes this much > easier to track.) > >> See attached. > > You're not actually changing the type of rootfs, you're overmounting it with > a second filesystem instance. (Mine hasn't got a "change", it just mounts it > correctly the first time, and there's just one rootfs instance.) > > What _is_ wrong with my version is that if you select tmpfs as a module bad > things happen; it tries to use code that's not there. I dunno of an #ifdef > that distinguishes between module and builtin, so I think I have to add > another kconfig symbol...
See include/linux/kconfig.h: IS_MODULE() and IS_BUILTIN(). > > I'll poke at it. -- ~Randy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
