Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [RFC][PATCH -mm] hibernation: freeze swap at hibernation (Was Re: Memory corruption during hibernation since 2.6.31 | Date | Mon, 2 Aug 2010 16:27:37 +0200 |
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On Monday, August 02, 2010, KAMEZAWA Hiroyuki wrote: > On Fri, 30 Jul 2010 13:14:32 +0900 > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > > > On Thu, 29 Jul 2010 21:10:10 -0700 > > Hugh Dickins <hughd@google.com> wrote: > > > > > On Thu, Jul 29, 2010 at 5:01 PM, KAMEZAWA Hiroyuki > > > <kamezawa.hiroyu@jp.fujitsu.com> wrote: > > > > > > > I think the best way is kexec(). But maybe rollback from hibernation failure > > > > will be difficult. Considering how crash-dump works well and under maintainance > > > > by many enterprise guys, hibernation-by-kexec is a choice. I think. It can make > > > > reuse of kdump code, ...or, hibernation-resume code can eat kdump image > > > > directly. Maybe the problem will be the speed of dump. > > > > > > I've no appetite for a total rework of hibernation, and I don't see > > > how that would > > > address the issue: I'm just looking for some protection against swap > > > reuse danger. > > > > > Okay ;) (And I forget that kexec has to prepare memory at boot time for 2nd kernel. > > It will be harmful for small device guys.) > > > > I'll prepare a routine not-quick-fix. > > Ok, here. Passed easy tests as > # echo disk > /sys/power/state > > > Looks like a big hammer ? But I think following kind of patch is required. > About swap-reuse, it's only possible when a page is added to swap cache > but try_to_unmap() fails and the page remains in memory. IIUC, most of this > kind of pages will be backed to swap by shrink_all_memory(). So, reuse-swap > happens only when the user unlucky. This patch ignores reuse-swap but freeze > swap_map[] for saving swap_map[] to the disk in consistent way. > > == > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > > swap_map[] is a one of objects which can be update while hibernation. I.E, > usage counter in swap_map[] is updated while hibernation is making a copy > of memory image to the disk. > > At resume, hibenation code doesn't call swap_free() against the swaps they > used...So, the swap_map[] will turns to be an initial state. > > With small consideration, the question is how swap_map[] updated before > dumping to the disk is treated. In swap-system view, there are no guarantee > that swap_map[] are properly reloaded and there is no leak in swap count. > > This patch tries to freeze swap_map[] during hibernation. > By this, no updates will be happen to swap_map[] among save_image(). > At load_image(), the swap_map[] has no record for swap entries used by > save_image(), we can simply forget it. > > Note: I'm not a specialist of hibernation...so, I'm not sure the hooks > to kernel/power/user.c is appropriate or not. > And this disables swap-out once hibernation starts saving. > Should we afraid of OOM ?
OOM shoiuld not happen at that time, so no worry.
I'll have a deeper look into the patch later today.
Thanks, Rafael
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