Messages in this thread | | | Date | Thu, 15 Jun 2017 10:24:10 +0200 | From | Michal Hocko <> | Subject | Re: [PATCH] mm, memory_hotplug: support movable_node for hotplugable nodes |
| |
On Thu 15-06-17 11:29:27, Wei Yang wrote: [...] > >+static inline bool movable_pfn_range(int nid, struct zone *default_zone, > >+ unsigned long start_pfn, unsigned long nr_pages) > >+{ > >+ if (!allow_online_pfn_range(nid, start_pfn, nr_pages, > >+ MMOP_ONLINE_KERNEL)) > >+ return true; > >+ > >+ if (!movable_node_is_enabled()) > >+ return false; > >+ > >+ return !zone_intersects(default_zone, start_pfn, nr_pages); > >+} > >+ > > To be honest, I don't understand this clearly. > > move_pfn_range() will choose and move the range to a zone based on the > online_type, where we have two cases: > 1. ONLINE_MOVABLE -> ZONE_MOVABLE will be chosen > 2. ONLINE_KEEP -> ZONE_NORMAL is the default while ZONE_MOVABLE will be > chosen in case movable_pfn_range() returns true. > > There are three conditions in movable_pfn_range(): > 1. Not allowed in kernel_zone, returns true > 2. Movable_node not enabled, return false > 3. Range [start_pfn, start_pfn + nr_pages) doesn't intersect with > default_zone, return true > > The first one is inherited from original code, so lets look at the other two. > > Number 3 is easy to understand, if the hot-added range is already part of > ZONE_NORMAL, use it. > > Number 2 makes me confused. If movable_node is not enabled, ZONE_NORMAL will > be chosen. If movable_node is enabled, it still depends on other two > condition. So how a memory_block is onlined to ZONE_MOVABLE because > movable_node is enabled?
This is simple. If the movable_node is set then ONLINE_KEEP defaults to the movable zone unless the range is already covered by a kernel zone (read Normal zone most of the time).
> What I see is you would forbid a memory_block to be > onlined to ZONE_MOVABLE when movable_node is not enabled.
Please note that this is ONLINE_KEEP not ONLINE_MOVABLE and as such the movable zone is used only if we are withing the movable zone range already (test 1).
> Instead of you would > online a memory_block to ZONE_MOVABLE when movable_node is enabled, which is > implied in your change log. > > BTW, would you mind giving me these two information? > 1. Which branch your code is based on? I have cloned your > git(//git.kernel.org/pub/scm/linux/kernel/git/mhocko/mm.git), while still see > some difference.
yes this is based on the mmotm tree (use since-4.11 or auto-latest branch)
> 2. Any example or test case I could try your patch and see the difference? It > would be better if it could run in qemu+kvm.
See http://lkml.kernel.org/r/20170421120512.23960-1-mhocko@kernel.org -- Michal Hocko SUSE Labs
| |