On Sun, Aug 4, 2013 at 4:07 AM, Michal Hocko <mhocko@xxxxxxx> wrote: > On Sat 03-08-13 16:16:58, KOSAKI Motohiro wrote: >> >>> You missed the "!". I'm proposing that setting the new bit 2 will >> >>> permit people to prevent the new printk if it is causing them problems. >> >> >> >> No I don't. I'm sure almost all abuse users think our usage is correct. Then, >> >> I can imagine all crazy applications start to use this flag eventually. >> > >> > I guess we do not care about those. If somebody wants to shoot his feet >> > then we cannot do much about it. The primary motivation was to find out >> > those that think this is right and they are willing to change the setup >> > once they know this is not the right way to do things. >> > >> > I think that giving a way to suppress the warning is a good step. Log >> > level might be to coarse and sysctl would be an overkill. >> >> When Dave Hansen reported this issue originally, he explained a lot of userland >> developer misuse /proc/drop_caches because they don't understand what >> drop_caches do. >> So, if they never understand the fact, why can we trust them? I have no >> idea. > > Well, most of that usage I have come across was legacy scripts which > happened to work at a certain point in time because we sucked. > Thinks have changed but such scripts happen to survive a long time. > We are primarily interested in those. Well, if the main target is shell script, task_comm and pid don't help us a lot. I suggest to add ppid too. > >> Or, if you have different motivation w/ Dave, please let me know it. > > We have seen reports where users complained about performance drop down > when in fact the real culprit turned out to be such a clever script > which dropped caches on the background thinking it will help to free > some memory. Such cases are tedious to reveal. Imagine such script have bit-2 and no logging output. Because the script author think "we are doing the right thing". Why distro guys want such suppress messages? >> While the purpose is to shoot misuse, I don't think we can trust >> userland app. If "If somebody wants to shoot his feet then we cannot >> do much about it." is true, this patch is useless. OK, we still catch >> the right user. > > I do not think it is useless. It will print a message for all those > users initially. It is a matter of user how to deal with it. If it is userland matter, we don't need additional logging at all. userland can write their own log. Again, if a crazy guys write blog "Hey! we should use echo 7 > /proc/sys/vm/drop_caches" always, we will come back the original problem. You and Dave wrote we need to care wrong, rumor and crazy drop_caches usage. And if so, you need to think new additional crazy rumor. >> But we never want to know who is the right users, right? > > Well, those that are curious about a new message in the lock and come > back to us asking what is going on are those we are primarily interested > in. I didn't say the message is useless. I did say hidden drop-cache user is useless. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>