1. 04 Dec, 2019 1 commit
  2. 12 Dec, 2017 1 commit
    • Kirill Smelkov's avatar
      virtmem: Benchmarks for pagefault handling · 3cfc2728
      Kirill Smelkov authored
      Benchmark the time it takes for virtmem to handle pagefault with noop
      loadblk for loadblk both implemented in C and in Python.
      
      On my computer it is:
      
      	name          µs/op
      	PagefaultC    269 ± 0%
      	pagefault_py  291 ± 0%
      
      Quite a big time in other words.
      
      It turned out to be mostly spent in fallocate'ing pages on tmpfs from
      /dev/shm. Part of the above 269 µs/op is taken by freeing (reclaiming)
      pages back when benchmarking work size exceed /dev/shm size, and part to
      allocating.
      
      If I limit the work size (via npage in benchmem.c) to be less than whole
      /dev/shm it starts to be ~ 170 µs/op and with additional tracing it
      shows as something like this:
      
          	.. on_pagefault_start   0.954 µs
          	.. vma_on_pagefault_pre 0.954 µs
          	.. ramh_alloc_page_pre  0.954 µs
          	.. ramh_alloc_page      169.992 µs
          	.. vma_on_pagefault     172.853 µs
          	.. vma_on_pagefault_pre 172.853 µs
          	.. vma_on_pagefault     174.046 µs
          	.. on_pagefault_end     174.046 µs
          	.. whole:               171.900 µs
      
      so almost all time is spent in ramh_alloc_page which is doing the fallocate:
      
      	https://lab.nexedi.com/nexedi/wendelin.core/blob/f11386a4/bigfile/ram_shmfs.c#L125
      
      Simple benchmark[1] confirmed it is indeed the case for fallocate(tmpfs) to be
      relatively slow[2] (and that for recent kernels it regressed somewhat
      compared to Linux 3.16). Profile flamegraph for that benchmark[3] shows
      internal loading of shmem_fallocate which for 1 hardware page is not
      that too slow (e.g. <1µs) but when a request comes for a region
      internally performs it page by page and so accumulates that ~ 170µs for 2M.
      
      I've tried to briefly rerun the benchmark with huge pages activated on /dev/shm via
      
      	mount /dev/shm -o huge=always,remount
      
      as both regular user and as root but it was executing several times
      slower. Probably something to investigate more later.
      
      [1] https://lab.nexedi.com/kirr/misc/blob/4f84a06e/tmpfs/t_fallocate.c
      [2] https://lab.nexedi.com/kirr/misc/blob/4f84a06e/tmpfs/1.txt
      [3] https://lab.nexedi.com/kirr/misc/raw/4f84a06e/tmpfs/fallocate-2M-nohuge.svg
      3cfc2728
  3. 24 Oct, 2017 1 commit
    • Kirill Smelkov's avatar
      Relicense to GPLv3+ with wide exception for all Free Software / Open Source... · f11386a4
      Kirill Smelkov authored
      Relicense to GPLv3+ with wide exception for all Free Software / Open Source projects + Business options.
      
      Nexedi stack is licensed under Free Software licenses with various exceptions
      that cover three business cases:
      
      - Free Software
      - Proprietary Software
      - Rebranding
      
      As long as one intends to develop Free Software based on Nexedi stack, no
      license cost is involved. Developing proprietary software based on Nexedi stack
      may require a proprietary exception license. Rebranding Nexedi stack is
      prohibited unless rebranding license is acquired.
      
      Through this licensing approach, Nexedi expects to encourage Free Software
      development without restrictions and at the same time create a framework for
      proprietary software to contribute to the long term sustainability of the
      Nexedi stack.
      
      Please see https://www.nexedi.com/licensing for details, rationale and options.
      f11386a4
  4. 03 Apr, 2015 2 commits
    • Kirill Smelkov's avatar
      bigfile/virtmem: Userspace Virtual Memory Manager · 9a293c2d
      Kirill Smelkov authored
      Does similar things to what kernel does - users can mmap file parts into
      address space and access them read/write. The manager will be getting
      invoked by hardware/OS kernel for cases when there is no page loaded for
      read, or when a previousle read-only page is being written to.
      
      Additionally to features provided in kernel, it support to be used to
      store back changes in transactional way (see fileh_dirty_writeout()) and
      potentially use huge pages for mappings (though this is currently TODO)
      9a293c2d
    • Kirill Smelkov's avatar
      bigfile/types.h: Type's we'll use · 8114ad6c
      Kirill Smelkov authored
      8114ad6c