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    SubjectRe: [PATCH] add some drop_caches documentation and info messsge
    On Fri, Oct 12, 2012 at 8:57 AM, Michal Hocko <mhocko@suse.cz> 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@linux.vnet.ibm.com>
    > 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@suse.cz: refreshed to current -mm tree]
    > Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>
    > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > Acked-by: Michal Hocko <mhocko@suse.cz>

    Looks fine.

    Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>


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