[PATCH v4 0/8] kdump, vmcore: support mmap() on /proc/vmcore

HATAYAMA Daisuke d.hatayama at jp.fujitsu.com
Fri Apr 12 20:21:05 EDT 2013

Currently, read to /proc/vmcore is done by read_oldmem() that uses
ioremap/iounmap per a single page. For example, if memory is 1GB,
ioremap/iounmap is called (1GB / 4KB)-times, that is, 262144
times. This causes big performance degradation.

In particular, the current main user of this mmap() is makedumpfile,
which not only reads memory from /proc/vmcore but also does other
processing like filtering, compression and IO work.

To address the issue, this patch implements mmap() on /proc/vmcore to
improve read performance.


You can see two benchmarks on terabyte memory system. Both show about
40 seconds on 2TB system. This is almost equal to performance by
experimtanal kernel-side memory filtering.

- makedumpfile mmap() benchmark, by Jingbai Ma

- makedumpfile: benchmark on mmap() with /proc/vmcore on 2TB memory system


v3 => v4)

- Rebase 3.9-rc7.
- Drop clean-up patches orthogonal to the main topic of this patch set.
- Copy ELF note segments in the 1st kernel just as in v1. Allocate
  vmcore objects per pages. => See [PATCH 5/8]
- Map memory referenced by PT_LOAD entry directly even if the start or
  end of the region doesn't fit inside page boundary, no longer copy
  them as the previous v3. Then, holes, outside OS memory, are visible
  from /proc/vmcore. => See [PATCH 7/8]

v2 => v3)

- Rebase 3.9-rc3.
- Copy program headers seprately from e_phoff in ELF note segment
  buffer. Now there's no risk to allocate huge memory if program
  header table positions after memory segment.
- Add cleanup patch that removes unnecessary variable.
- Fix wrongly using the variable that is buffer size configurable at
  runtime. Instead, use the varibale that has original buffer size.

v1 => v2)

- Clean up the existing codes: use e_phoff, and remove the assumption
  on PT_NOTE entries.
- Fix potencial bug that ELF haeader size is not included in exported
  vmcoreinfo size.
- Divide patch modifying read_vmcore() into two: clean-up and primary
  code change.
- Put ELF note segments in page-size boundary on the 1st kernel
  instead of copying them into the buffer on the 2nd kernel.


This patch set is composed based on v3.9-rc7.

Done on x86-64, x86-32 both with 1GB and over 4GB memory environments.


HATAYAMA Daisuke (8):
      vmcore: support mmap() on /proc/vmcore
      vmcore: treat memory chunks referenced by PT_LOAD program header entries in page-size boundary in vmcore_list
      vmcore: count holes generated by round-up operation for page boudary for size of /proc/vmcore
      vmcore: copy ELF note segments in the 2nd kernel per page vmcore objects
      vmcore: Add helper function vmcore_add()
      vmcore, procfs: introduce MEM_TYPE_CURRENT_KERNEL flag to distinguish objects copied in 2nd kernel
      vmcore: clean up read_vmcore()
      vmcore: allocate buffer for ELF headers on page-size alignment

 fs/proc/vmcore.c        |  349 ++++++++++++++++++++++++++++++++---------------
 include/linux/proc_fs.h |    8 +
 2 files changed, 245 insertions(+), 112 deletions(-)



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