Andrew Morton wrote:
Christoph Lameter <[email protected]> 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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