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Subject[PATCH v2 00/20] kdump, vmcore: support mmap() on /proc/vmcore
Date
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. Update of page
table and the following TLB flush makes such processing much slow;
though I have yet to make patch for makedumpfile and yet to confirm
how it's improved.

To address the issue, this patch implements mmap() on /proc/vmcore to
improve read performance. My simple benchmark shows the improvement
from 200 [MiB/sec] to over 50.0 [GiB/sec].

ChangeLog
=========

v1 => v2)

- Clean up the existing codes: use e_phoff, and remove the assumption
on PT_NOTE entries.
=> See PATCH 01, 02.

- Fix potencial bug that ELF haeader size is not included in exported
vmcoreinfo size.
=> See Patch 03.

- Divide patch modifying read_vmcore() into two: clean-up and primary
code change.
=> See Patch 9, 10.

- Put ELF note segments in page-size boundary on the 1st kernel
instead of copying them into the buffer on the 2nd kernel.
=> See Patch 11, 12, 13, 14, 16.

Benchmark
=========

No change is seen from the previous patch series. See the previous
one from here:

https://lkml.org/lkml/2013/2/14/89

TODO
====

- fix makedumpfile to use mmap() on /proc/vmcore and benchmark it to
confirm whether we can see enough performance improvement. The idea
is described here:
http://lists.infradead.org/pipermail/kexec/2013-February/007982.html

- fix crash utility and makedumpfile to support NT_VMCORE_PAD note
type. Both tools don't distinguish the same note types from
different note names, which is not conform to ELF specification; now
both reads NT_VMCORE_PAD note type as NT_VMCORE_DEBUGINFO.

Test
====

This patch set is composed based on v3.9-rc1.

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

---

HATAYAMA Daisuke (20):
vmcore: introduce mmap_vmcore()
vmcore: count holes generated by round-up operation for vmcore size
vmcore: round-up offset of vmcore object in page-size boundary
vmcore: check if vmcore objects satify mmap()'s page-size boundary requirement
vmcore: check NT_VMCORE_PAD as a mark indicating the end of ELF note buffer
kexec: fill note buffers by NT_VMCORE_PAD notes in page-size boundary
elf: introduce NT_VMCORE_PAD type
kexec, elf: introduce NT_VMCORE_DEBUGINFO note type
kexec: allocate vmcoreinfo note buffer on page-size boundary
vmcore: allocate per-cpu crash_notes objects on page-size boundary
vmcore: read buffers for vmcore objects copied from old memory
vmcore: clean up read_vmcore()
vmcore: modify vmcore clean-up function to free buffer on 2nd kernel
vmcore: copy non page-size aligned head and tail pages in 2nd kernel
vmcore, procfs: introduce a flag to distinguish objects copied in 2nd kernel
vmcore: round up buffer size of ELF headers by PAGE_SIZE
vmcore: allocate buffer for ELF headers on page-size alignment
vmcore, sysfs: export ELF note segment size instead of vmcoreinfo data size
vmcore: rearrange program headers without assuming consequtive PT_NOTE entries
vmcore: refer to e_phoff member explicitly


arch/s390/include/asm/kexec.h | 7
fs/proc/vmcore.c | 577 ++++++++++++++++++++++++++++++++---------
include/linux/kexec.h | 16 +
include/linux/proc_fs.h | 8 -
include/uapi/linux/elf.h | 5
kernel/kexec.c | 47 ++-
kernel/ksysfs.c | 2
7 files changed, 505 insertions(+), 157 deletions(-)

--
Thanks.
HATAYAMA, Daisuke


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