[RFC PATCH 0/4] mm: Add PG_zero support

[liliangleo]

Zero out the page content usually happens when allocating pages,
this is a time consuming operation, it makes pin and mlock
operation very slowly, especially for a large batch of memory.

This patch introduce a new feature for zero out pages before page
allocation, it can help to speed up page allocation.

The idea is very simple, zero out free pages when the system is
not busy and mark the page with PG_zero, when allocating a page,
if the page need to be filled with zero, check the flag in the
struct page, if it's marked as PG_zero, zero out can be skipped,
it can save cpu time and speed up page allocation.

This serial is based on the feature 'free page reporting' which
introduced by Alexander Duyck 

We can benefit from this feature in the flowing case:
    1. User space mlock a large chunk of memory
    2. VFIO pin pages for DMA
    3. Allocating transparent huge page
    4. Speed up page fault process

My original intention for adding this feature is to shorten
VM creation time when VFIO device is attached, it works good 
and the VM creation time is reduced obviously. 

Creating a VM [64G RAM, 32 CPUs] with GPU passthrough
=====================================================
QEMU use 4K pages, THP is off
                  round1      round2      round3
w/o this patch:    23.5s       24.7s       24.6s 
w/ this patch:     10.2s       10.3s       11.2s

QEMU use 4K pages, THP is on
                  round1      round2      round3
w/o this patch:    17.9s       14.8s       14.9s 
w/ this patch:     1.9s        1.8s        1.9s
=====================================================

Look forward to your feedbacks.

Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>  
Cc: Michal Hocko <mhocko@xxxxxxxxxx> 
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
Signed-off-by: liliangleo <liliangleo@xxxxxxxxxxxxxx>

liliangleo (4):
  mm: reduce the impaction of page reporing worker
  mm: Add batch size for free page reporting
  mm: add sys fs configuration for page reporting
  mm: Add PG_zero support

 include/linux/highmem.h        |  31 ++++++-
 include/linux/page-flags.h     |  18 +++-
 include/trace/events/mmflags.h |   7 ++
 mm/Kconfig                     |  10 +++
 mm/Makefile                    |   1 +
 mm/huge_memory.c               |   3 +-
 mm/page_alloc.c                |   2 +
 mm/page_reporting.c            | 181 +++++++++++++++++++++++++++++++++++++++--
 mm/page_reporting.h            |  16 +++-
 mm/zero_page.c                 | 151 ++++++++++++++++++++++++++++++++++
 mm/zero_page.h                 |  13 +++
 11 files changed, 416 insertions(+), 17 deletions(-)
 create mode 100644 mm/zero_page.c
 create mode 100644 mm/zero_page.h

-- 
2.14.1