On Thu, 31 Mar 2011 10:57:19 +0800 Shaohua Li <shaohua.li@xxxxxxxxx> wrote: > On Thu, 2011-03-31 at 10:34 +0800, Andrew Morton wrote: > > On Thu, 31 Mar 2011 08:56:43 +0800 Shaohua Li <shaohua.li@xxxxxxxxx> wrote: > > > > > > This is a big change, and it wasn't even changelogged. It's > > > > potentially a tremendous increase in the expense of a read from > > > > /proc/meminfo, which is a file that lots of tools will be polling. > > > > Many of those tools we don't even know about or have access to. > > > Assume we don't read /proc/meminfo too often. > > > > That's a poor assumption. top(1) and vmstat(8) read it, for a start. > > There will be zillions of locally-developed monitoring tools which read > > meminfo. > > > > Now, it could be that something under meminfo reads _already_ does a > > massive walk across all CPUs. If so then we'll have already trained > > people to avoid reading /proc/meminfo and this change might be > > acceptable. > > > > But if this isn't the case then it's quite likely that this change will > > hurt some people quite a lot. And, unfortunately, the sort of people > > who we will hurt tend to be people who don't run our stuff until a long > > time (years) after we wrote it. By which time it's going to be quite > > expensive to get a fix down the chain and into their hands. > Just looked at the code. nr_blockdev_pages() of si_meminfo iterate all > block devices. For people who care about the time, their system must > have more block devices than CPUs. How can we be sure of that? > so this isn't a big issue? Well it might be. Experience tells us that some people are likely to get bitten by this. It's far safer and saner to find a solution which doesn't have big fat failure modes! Also, we don't (yet) know what we're *gaining* for this big fat failure mode. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>