Messages in this thread | | | Date | Thu, 10 Dec 2009 08:54:13 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH 2/9] ksm: let shared pages be swappable |
| |
On Wed, 9 Dec 2009 17:12:19 +0100 Andrea Arcangeli <aarcange@redhat.com> wrote:
> On Wed, Dec 09, 2009 at 09:43:31AM +0900, KAMEZAWA Hiroyuki wrote: > > cache-line ping-pong at fork beacause of page->mapcount. And KSM introduces > > zero-pages which have mapcount again. If no problems in realitsitc usage of > > KVM, ignore me. > > The whole memory marked MADV_MERGEABLE by KVM is also marked > MADV_DONTFORK, so if KVM was to fork (and if it did, if it wasn't for > MADV_DONTFORK, it would also trigger all O_DIRECT vs fork race > conditions too, as KVM is one of the many apps that uses threads and > O_DIRECT - we try not to fork though but we sure did in the past), no > slowdown could ever happen in mapcount because of KSM, all KSM pages > aren't visibile by child. > > It's still something to keep in mind for other KSM users, but I don't > think mapcount is big deal if compared to the risk of triggering COWs > later on those pages, in general KSM is all about saving tons of > memory at the expense of some CPU cycle (kksmd, cows, mapcount with > parallel forks etc...). > Okay, thank you for kindlt explanation.
and sorry for noise.
Thanks, -Kame
| |