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
