(2012/10/12 21:57), Michal Hocko wrote:
Hi, I would like to resurrect the following Dave's patch. The last time it has been posted was here https://lkml.org/lkml/2010/9/16/250 and there didn't seem to be any strong opposition. Kosaki was worried about possible excessive logging when somebody drops caches too often (but then he claimed he didn't have a strong opinion on that) but I would say opposite. If somebody does that then I would really like to know that from the log when supporting a system because it almost for sure means that there is something fishy going on. It is also worth mentioning that only root can write drop caches so this is not an flooding attack vector. I am bringing that up again because this can be really helpful when chasing strange performance issues which (surprise surprise) turn out to be related to artificially dropped caches done because the admin thinks this would help... I have just refreshed the original patch on top of the current mm tree but I could live with KERN_INFO as well if people think that KERN_NOTICE is too hysterical. --- From 1f4058be9b089bc9d43d71bc63989335d7637d8d Mon Sep 17 00:00:00 2001 From: Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> Date: Fri, 12 Oct 2012 14:30:54 +0200 Subject: [PATCH] add some drop_caches documentation and info messsge There is plenty of anecdotal evidence and a load of blog posts suggesting that using "drop_caches" periodically keeps your system running in "tip top shape". Perhaps adding some kernel documentation will increase the amount of accurate data on its use. If we are not shrinking caches effectively, then we have real bugs. Using drop_caches will simply mask the bugs and make them harder to find, but certainly does not fix them, nor is it an appropriate "workaround" to limit the size of the caches. It's a great debugging tool, and is really handy for doing things like repeatable benchmark runs. So, add a bit more documentation about it, and add a little KERN_NOTICE. It should help developers who are chasing down reclaim-related bugs. [mhocko@xxxxxxx: refreshed to current -mm tree] Signed-off-by: Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxx>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> -- 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>