[v2 0/1] Allow deferred page initialization for xen pv domains

[Pavel Tatashin <pasha.tatashin@oracle.com>]

Changelog
v1 - v2
- Addressed coomment from Juergen Gross: fixed a comment, and moved
  after_bootmem from PV framework to x86_init.hyper.

>From this discussion:
https://www.spinics.net/lists/linux-mm/msg145604.html

I investigated whether it is feasible to re-enable deferred page
initialization on xen's para-vitalized domains. After studying the
code, I found non-intrusive way to do just that.

All we need to do is to assume that page-table's pages are pinned early in
boot, which is always true, and add a new x86_init.hyper OP call to notify
guests that boot allocator is finished, so we can set all the necessary
fields in already initialized struct pages.

I have tested this on my laptop with 64-bit kernel, but I would appreciate
if someone could provide more xen testing.

Apply against: linux-next. Enable the following configs:

CONFIG_XEN_PV=y
CONFIG_DEFERRED_STRUCT_PAGE_INIT=y
The above two are needed to test deferred page initialization on PV Xen
domains. If fix is applied correctly, dmesg should output line(s) like this
during boot:
[    0.266180] node 0 initialised, 717570 pages in 36ms

CONFIG_DEBUG_VM=y
This is needed to poison struct page's memory, otherwise it would be all
zero.

CONFIG_DEBUG_VM_PGFLAGS=y
Verifies that we do not access struct pages flags while memory is still
poisoned (struct pages are not initialized yet).

Pavel Tatashin (1):
  xen, mm: Allow deferred page initialization for xen pv domains

 arch/x86/include/asm/x86_init.h |  2 ++
 arch/x86/kernel/x86_init.c      |  1 +
 arch/x86/mm/init_32.c           |  1 +
 arch/x86/mm/init_64.c           |  1 +
 arch/x86/xen/mmu_pv.c           | 38 ++++++++++++++++++++++++++------------
 mm/page_alloc.c                 |  4 ----
 6 files changed, 31 insertions(+), 16 deletions(-)

-- 
2.16.2

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