Messages in this thread | | | Date | Fri, 21 Oct 2005 14:59:14 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH 0/4] Swap migration V3: Overview |
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Andrew Morton wrote: > Christoph Lameter <clameter@sgi.com> wrote: > >>Page migration is also useful for other purposes: >> >> 1. Memory hotplug. Migrating processes off a memory node that is going >> to be disconnected. >> >> 2. Remapping of bad pages. These could be detected through soft ECC errors >> and other mechanisms. > > > It's only useful for these things if it works with close-to-100% reliability. > > And there are are all sorts of things which will prevent that - mlock, > ongoing direct-io, hugepages, whatever. > In lhms tree, current status is below: (If I'm wrong, plz fix) == For mlock, direct page migration will work fine. try_to_unmap_one() in -mhp tree has an argument *force* and ignore VM_LOCKED, it's for this.
For direct-io, we have to wait for completion. The end of I/O is not notified and memory_migrate() is just polling pages.
For hugepages, we'll need hugepage demand paging and more work, I think. ==
When a process migrates to other nodes by hand, it can cooperate with migration subsystem. So we don't have to be afraid of some special using of memory, in many case. I think Christoph's approach will work fine.
When it comes to memory-hotplug, arbitrary processes are affected. It's more difficult.
We should focus on 'process migraion on demand', in this thread.
-- Kame
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