[v1 0/1] Allow deferred page initialization for xen pv

From: Pavel Tatashin
Date: Fri Feb 23 2018 - 18:26:40 EST


>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 PV 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 initalization for xen pv domains

arch/x86/include/asm/paravirt.h | 9 +++++++++
arch/x86/include/asm/paravirt_types.h | 3 +++
arch/x86/kernel/paravirt.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 ----
7 files changed, 41 insertions(+), 16 deletions(-)

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2.16.2