On Sat, Apr 11, 2015 at 01:09:06AM +0300, Alexey Dobriyan wrote: > On Fri, Apr 10, 2015 at 02:01:32PM -0400, Jarod Wilson wrote: > > On Fri, Apr 10, 2015 at 05:13:29PM +0300, Alexey Dobriyan wrote: > > > /proc/$PID/cmdline truncates output at PAGE_SIZE. It is easy to see with > > > > > > $ cat /proc/self/cmdline $(seq 1037) 2>/dev/null > > > > > > However, command line size was never limited to PAGE_SIZE but to 128 KB > > > and > > > relatively recently limitation was removed altogether. > > > > > > People noticed and are asking questions: > > > http://stackoverflow.com/questions/199130/how-do-i-increase-the-proc-pid-cmdline-4096-byte-limit > > > > > > seq file interface is not OK, because it kmalloc's for whole output and > > > open + read(, 1) + sleep will pin arbitrary amounts of kernel memory. > > > To not do that, limit must be imposed which is incompatible with > > > arbitrary sized command lines. > > > > > > I apologize for hairy code, but this it direct consequence of command line > > > layout in memory and hacks to support things like "init [3]". > > > > > > The loops are "unrolled" otherwise it is either macros which hide > > > control flow or functions with 7-8 arguments with equal line count. > > > > That definitely qualifies as hairy. How big of a problem is it really in > > practice if we continued using seq_file though? This only happens when > > someone actually accesses /proc/$PID/cmdline, no? And if they're doing > > that, they probably want that info, so is it so terrible if memory is held > > on to for a bit? We're only talking about a few kB. That said, properly > > walking the entire cmdline without having to specify an arbitrary limit > > ahead of time does sound slightly more end-user-friendly. I'll give this > > patch a spin here. > > Well, it's 8 MB at least because of kmalloc and more when it starts > to vmalloc, so either you increase but keep the limit, or allow > to pin semi-arbitrary amount of kernel memory IF you want to stay > with seqfile. My patch requires just 1 page plus whatever g_u_p > requires.
Okay, I've tested this out some. Its definitely more user-friendly than having to require a boot param, and as a bonus, its even more memory-efficient. Yes, its a bit fugly, but such is life sometimes... Though I do wonder if this should perhaps be a helper in mm/util.c like get_cmdline, maybe replacing get_cmdline or adding an alternative that gives you everything, rather than an arbitrarily limited length. I only see one other place actually using get_cmdline so far. Tested-by: Jarod Wilson <ja...@redhat.com> Acked-by: Jarod Wilson <ja...@redhat.com> -- Jarod Wilson ja...@redhat.com -- 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/
