linux-kernel - [PATCH][0/2]page_fault retry with NOPAGE

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Date:	Wed, 8 Apr 2009 13:02:23 -0700
From:	Ying Han <yinghan@...gle.com>
To:	linux-mm@...ck.org, linux-kernel <linux-kernel@...r.kernel.org>,
	akpm <akpm@...ux-foundation.org>, torvalds@...ux-foundation.org,
	Ingo Molnar <mingo@...e.hu>, Mike Waychison <mikew@...gle.com>,
	Rohit Seth <rohitseth@...gle.com>,
	Hugh Dickins <hugh@...itas.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"H. Peter Anvin" <hpa@...or.com>,
	Török Edwin <edwintorok@...il.com>,
	Lee Schermerhorn <lee.schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>,
	Wu Fengguang <fengguang.wu@...el.com>
Subject: [PATCH][0/2]page_fault retry with NOPAGE_RETRY

changelog[v3]:
- applied fixes and cleanups from Wu Fengguang.
filemap VM_FAULT_RETRY fixes
[PATCH 01/14] mm: fix find_lock_page_retry() return value parsing
[PATCH 02/14] mm: fix major/minor fault accounting on retried fault
[PATCH 04/14] mm: reduce duplicate page fault code
[PATCH 05/14] readahead: account mmap_miss for VM_FAULT_RETRY

- split the patch into two parts. first part includes FAULT_FLAG_RETRY
  support with no current user change. second part includes individual
  per-architecture cleanups that enable FAULT_FLAG_RETRY.
  currently there are mainly two users for handle_mm_fault, we enable
  FAULT_FLAG_RETRY for actual fault handler and leave get_user_pages
  unchanged.

Benchmarks:
posted on [V1]:
case 1. one application has a high count of threads each faulting in
different pages of a hugefile. Benchmark indicate that this double data
structure walking in case of major fault results in << 1% performance hit.

case 2. add another thread in the above application which in a tight loop
of
mmap()/munmap(). Here we measure loop count in the new thread while other
threads doing the same amount of work as case one. we got << 3% performance
hit on the Complete Time(benchmark value for case one) and 10% performance
improvement on the mmap()/munmap() counter.

This patch helps a lot in cases we have writer which is waitting behind all
readers, so it could execute much faster.

some new test results from Wufengguang:
Just tested the sparse-random-read-on-sparse-file case, and found the
performance impact to be 0.4% (8.706s vs 8.744s). Kind of acceptable.

without FAULT_FLAG_RETRY:
iotrace.rb --load stride-100 --mplay /mnt/btrfs-ram/sparse  3.28s user
5.39s system 99% cpu 8.692 total
iotrace.rb --load stride-100 --mplay /mnt/btrfs-ram/sparse  3.17s user
5.54s system 99% cpu 8.742 total
iotrace.rb --load stride-100 --mplay /mnt/btrfs-ram/sparse  3.18s user
5.48s system 99% cpu 8.684 total

FAULT_FLAG_RETRY:
iotrace.rb --load stride-100 --mplay /mnt/btrfs-ram/sparse  3.18s user
5.63s system 99% cpu 8.825 total
iotrace.rb --load stride-100 --mplay /mnt/btrfs-ram/sparse  3.22s user
5.47s system 99% cpu 8.718 total
iotrace.rb --load stride-100 --mplay /mnt/btrfs-ram/sparse  3.13s user
5.55s system 99% cpu 8.690 total

In the above faked workload, the mmap read page offsets are loaded from
stride-100 and performed on /mnt/btrfs-ram/sparse, which are created by:

	seq 0 100 1000000 > stride-100
	dd if=/dev/zero of=/mnt/btrfs-ram/sparse bs=1M count=1 seek=1024000

Signed-off-by: Ying Han <yinghan@...gle.com>
	       Mike Waychison <mikew@...gle.com>

 arch/x86/mm/fault.c |   20 ++++++++++++++
 include/linux/fs.h  |    2 +-
 include/linux/mm.h  |    2 +
 mm/filemap.c        |   72 ++++++++++++++++++++++++++++++++++++++++++++++++--
 mm/memory.c         |   33 +++++++++++++++++------
 5 files changed, 116 insertions(+), 13 deletions(-)
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