Messages in this thread | | | From | Matthew Von Maszewski <> | Subject | huge mem mmap eats all CPU when multiple processes | Date | Mon, 8 Jun 2009 10:27:49 -0400 |
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[note: not on kernel mailing list, please cc author]
Symptom: 9 processes mmap same 2 Gig memory section for a shared C heap (lots of random access). All process begin extreme CPU load in top.
- Same code works well when only single process access huge mem. - Code works well with standard vm based mmap file and 9 processes.
Environment:
- Intel x86_64: Dual core Xeon with hyperthreading (4 logical processors) - 6 Gig ram, 2.5G allocated to huge mem - tried with kernels 2.6.29.4 and 2.6.30-rc8 - following mmap() call has base address as NULL on first process, then returned address passed to subsequent processes (not threads, processes)
m_MemSize=((m_MemSize/(2048*1024))+1)*2048*1024; m_BaseAddr=mmap(m_File->GetFixedBase(), m_MemSize, (PROT_READ | PROT_WRITE), MAP_SHARED, m_File->GetFileId(), m_Offset);
I am not a kernel hacker so I have not attempted to debug. Will be able to spend time on a sample program for sharing later today or tomorrow. Sending this note now in case this is already known.
Don't suppose this is as simple as a Copy-On-Write flag being set wrong?
Please send notes as to things I need to capture to better describe this bug. Happy to do the work.
Thanks, Matthew
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