On Mon, Nov 03, 2008 at 02:34:25PM -0800, Dave Hansen wrote: > On Mon, 2008-11-03 at 23:24 +0100, Rafael J. Wysocki wrote: > > On Monday, 3 of November 2008, Dave Hansen wrote: > > > On Mon, 2008-11-03 at 12:51 -0800, Andrew Morton wrote: > > > > On Wed, 29 Oct 2008 13:25:00 +0100 > > > > "Rafael J. Wysocki" <rjw@xxxxxxx> wrote: > > > > > On Wednesday, 29 of October 2008, Pavel Machek wrote: > > > > > > > > > > > > hibernation + memory hotplug was disabled in kconfig because we could > > > > > > not handle hibernation + sparse mem at some point. It seems to work > > > > > > now, so I guess we can enable it. > > > > > > > > > > OK, if "it seems to work now" means that it has been tested and confirmed to > > > > > work, no objection from me. > > > > > > > > yes, that was not a terribly confidence-inspiring commit message. > > > > > > > > 3947be1969a9ce455ec30f60ef51efb10e4323d1 said "For now, disable memory > > > > hotplug when swsusp is enabled. There's a lot of churn there right > > > > now. We'll fix it up properly once it calms down." which is also > > > > rather rubbery. > > > > > > > > Cough up, guys: what was the issue with memory hotplug and swsusp, and > > > > is it indeed now fixed? > > > > > > I suck. That commit message was horrid and I'm racking my brain now to > > > remember what I meant. Don't end up like me, kids. > > > > > > I've attached the message that I sent to the swsusp folks. I never got > > > a reply from that as far as I can tell. > > > > > > http://sourceforge.net/mailarchive/forum.php?thread_name=1118682535.22631.22.camel%40localhost&forum_name=lhms-devel > > > > > > As I look at it now, it hasn't improved much since 2005. Take a look at > > > kernel/power/snapshot.c::copy_data_pages(). It still assumes that the > > > list of zones that a system has is static. Memory hotplug needs to be > > > excluded while that operation is going on. > > > > This operation is carried out on one CPU with interrupts disabled. Is that > > not enough? > > If that's true then you don't need any locking for anything at all, > right? > > All of the changes I was talking about occur inside the kernel and code > has to run for it to happen. So, if you are saying that absolutely no > other code on the system can possibly run, then it should be OK. > > > > page_is_saveable() checks for pfn_valid(). But, with memory hotplug, > > > things can become invalid at any time since no references are held or > > > taken on the page. Or, a page that *was* invalid may become valid and > > > get missed. > > > > Can that really happen given the conditions above? > > Nope. > > But, as I think about it, there is another issue that we need to > address, CONFIG_NODES_SPAN_OTHER_NODES. > > A node might have a node_start_pfn=0 and a node_end_pfn=100 (and it may > have only one zone). But, there may be another node with > node_start_pfn=10 and a node_end_pfn=20. This loop: > > for_each_zone(zone) { > ... > for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) > if (page_is_saveable(zone, pfn)) > memory_bm_set_bit(orig_bm, pfn); > } > > will walk over the smaller node's pfn range multiple times. Is this OK? > > I think all you have to do to fix it is check page_zone(page) == zone > and skip out if they don't match. > > Andy, does anything else stick out to you? I agree that there needs to be a check for being in the zone there to avoid the overlapping nodes issue. Also need to make sure when constructing that check we check for pfn_valid before looking at the page to avoid holes in the memmap. -apw _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
