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Re: [PATCH v2 0/5] Allocate cache entries from memory pool

From
Stefan Beller <sbeller@google.com>
Date
May 3, 2018, 20:58 UTC
Message-ID
<CAGZ79kb1K9iysibzmn2SUfyTayXOn97wTsoL4s557j+_ievkBA@mail.gmail.com>
In-Reply-To
<CACsJy8DF40o3gesuNbHACK+NiE=iZuXxLacyEQjECYewDy_icw@mail.gmail.com>
On Thu, May 3, 2018 at 12:17 PM, Duy Nguyen <pclouds@gmail.com> wrote:
Show 5 quoted lines
>
>> To me it is also a clear yes when it comes to combining these
>> two memory pools.
>
> I also did not notice that jm/mem-pool already landed in master.
Oh, thanks for telling! Now that I look at it, I am doubting it;

The reason for my doubt is the potential quadratic behavior for new allocations, in mem_pool_alloc() we walk all mp_blocks to see if we can fit the requested allocation in one of the later blocks. So if we call mem_pool_alloc a million times, we get a O(n) mp_blocks which we'd have to walk in each call.

However in alloc.c we do know that a slab is full as soon as we look take the next slab. That is the beauty of knowing 'len' at construction time of the allocator.

So I guess I'll just re-use the mp_block and introduce another struct fixed_sized_mem_pool, which will not look into other mp_blocks but the current.

> Have
> you tried measure (both memory usage and allocation speed) of it and
> alloc.c?

No, I was about to, but then started reading the code in an attempt to replace alloc.c by a mempool and saw the quadratic behavior.

Show 10 quoted lines
> Just take some big repo as an example and do count-objects -v
> to see how many blobs/trees/commits it has, then allocate the same
> amount with both alloc.c and mem-pool.c and measure both speed/mem.
> I'm pretty sure you're right that mem-pool.c is a clear yes. I was
> just being more conservative because we do (slightly) change
> allocator's behavior when we make the switch. But it's also very
> likely that any performance difference will be insignificant.
>
> I'm asking this because if mem-pool.c is a clear winner, you can start
> to update you series to use it now and kill alloc.c in the process.
I'll implement the fixed_sized_mem_pool and take some measurements.
>
> PS. Is Jeff back yet?

His last email on the public list is Apr 10th, stating that he'll be offline for "a few weeks", in <20180406175349.GB32228@sigill.intra.peff.net> he said the vacation part is 3 weeks. So I think he is done with vacation and is just hiding to figure out a nice comeback. ;-)

> I'm sure Junio is listening and all but I'm
> afraid he's too busy being a maintainer so Jeff's opinion in this area
> is really valuable. He has all the fun and weird use cases to play
> with at github.
ok. I'll cc him for these patches.

Thanks, Stefan

Previous: Duy NguyenNext: Jameson Miller
Message 36 of 100 in “Allocate cache entries from memory pool”
  1. 0/5 Allocate cache entries from memory poolJameson Miller, Apr 17, 2018
  2. 0/5 Allocate cache entries from memory poolJameson Miller, Apr 17, 2018
  3. 2/5 Add an API creating / discarding cache_entry structsJameson Miller, Apr 17, 2018
  4. Ben PeartApr 17, 2018
  5. 1/5 read-cache: teach refresh_cache_entry to take istateJameson Miller, Apr 17, 2018
  6. Ben PeartApr 17, 2018
  7. 3/5 mem-pool: fill out functionalityJameson Miller, Apr 17, 2018
  8. Jonathan TanApr 20, 2018
  9. Jameson MillerApr 23, 2018
  10. Jonathan TanApr 23, 2018
  11. Jameson MillerApr 23, 2018
  12. 5/5 Add optional memory validations around cache_entry lifecyleJameson Miller, Apr 17, 2018
  13. 4/5 Allocate cache entries from memory poolsJameson Miller, Apr 17, 2018
  14. Ben PeartApr 17, 2018
  15. Jameson MillerApr 23, 2018
  16. Junio C HamanoApr 18, 2018
  17. Stefan BellerApr 20, 2018
  18. Jameson MillerApr 23, 2018
  19. Stefan BellerApr 23, 2018
  20. Jameson MillerApr 23, 2018
  21. Jonathan TanApr 20, 2018
  22. Jameson MillerApr 23, 2018
  23. 0/5 Allocate cache entries from memory poolJameson Miller, Apr 30, 2018
  24. 1/5 read-cache: teach refresh_cache_entry() to take istateJameson Miller, Apr 30, 2018
  25. 3/5 mem-pool: fill out functionalityJameson Miller, Apr 30, 2018
  26. Stefan BellerApr 30, 2018
  27. Jameson MillerMay 1, 2018
  28. Duy NguyenMay 3, 2018
  29. 5/5 block alloc: add validations around cache_entry lifecyleJameson Miller, Apr 30, 2018
  30. Duy NguyenMay 3, 2018
  31. 2/5 block alloc: add lifecycle APIs for cache_entry structsJameson Miller, Apr 30, 2018
  32. 4/5 block alloc: allocate cache entries from mem_poolJameson Miller, Apr 30, 2018
  33. Duy NguyenMay 3, 2018
  34. Stefan BellerMay 3, 2018
  35. Duy NguyenMay 3, 2018
  36. Stefan BellerMay 3, 2018
  37. Jameson MillerMay 3, 2018
  38. alloc.c: replace alloc by mempoolStefan Beller, May 3, 2018
  39. Duy NguyenMay 4, 2018
  40. Junio C HamanoMay 8, 2018
  41. Stefan BellerMay 8, 2018
  42. Junio C HamanoMay 8, 2018
  43. 0/7 allocate cache entries from memory poolJameson Miller, May 23, 2018
  44. 1/7 read-cache: teach refresh_cache_entry() to take istateJameson Miller, May 23, 2018
  45. Stefan BellerMay 25, 2018
  46. 3/7 mem-pool: only search head block for available spaceJameson Miller, May 23, 2018
  47. 2/7 block alloc: add lifecycle APIs for cache_entry structsJameson Miller, May 23, 2018
  48. Junio C HamanoMay 24, 2018
  49. Jameson MillerMay 24, 2018
  50. 4/7 mem-pool: add lifecycle management functionsJameson Miller, May 23, 2018
  51. 5/7 mem-pool: fill out functionalityJameson Miller, May 23, 2018
  52. Stefan BellerJun 1, 2018
  53. 6/7 block alloc: allocate cache entries from mem_poolJameson Miller, May 23, 2018
  54. 7/7 block alloc: add validations around cache_entry lifecyleJameson Miller, May 23, 2018
  55. Junio C HamanoMay 24, 2018
  56. Jameson MillerMay 24, 2018
  57. Stefan BellerMay 25, 2018
  58. Jameson MillerJun 20, 2018
  59. Stefan BellerMay 25, 2018
  60. 0/8 Allocate cache entries from mem_poolJameson Miller, Jun 20, 2018
  61. 1/8 read-cache: teach refresh_cache_entry() to take istateJameson Miller, Jun 20, 2018
  62. 3/8 mem-pool: only search head block for available spaceJameson Miller, Jun 20, 2018
  63. Stefan BellerJun 21, 2018
  64. Jameson MillerJun 28, 2018
  65. 5/8 mem-pool: add lifecycle management functionsJameson Miller, Jun 20, 2018
  66. 8/8 block alloc: add validations around cache_entry lifecyleJameson Miller, Jun 20, 2018
  67. 7/8 block alloc: allocate cache entries from mem_poolJameson Miller, Jun 20, 2018
  68. 4/8 mem-pool: tweak math on mp_block allocation sizeJameson Miller, Jun 20, 2018
  69. 2/8 block alloc: add lifecycle APIs for cache_entry structsJameson Miller, Jun 20, 2018
  70. Stefan BellerJun 21, 2018
  71. Jameson MillerJun 28, 2018
  72. 6/8 mem-pool: fill out functionalityJameson Miller, Jun 20, 2018
  73. 0/8 Allocate cache entries from mem_poolJameson Miller, Jun 28, 2018
  74. 2/8 read-cache: make_cache_entry should take object_id structJameson Miller, Jun 28, 2018
  75. Junio C HamanoJun 28, 2018
  76. SZEDER GáborJun 28, 2018
  77. 3/8 block alloc: add lifecycle APIs for cache_entry structsJameson Miller, Jun 28, 2018
  78. Junio C HamanoJun 28, 2018
  79. SZEDER GáborJun 28, 2018
  80. 5/8 mem-pool: add life cycle management functionsJameson Miller, Jun 28, 2018
  81. Junio C HamanoJun 28, 2018
  82. 4/8 mem-pool: only search head block for available spaceJameson Miller, Jun 28, 2018
  83. 6/8 mem-pool: fill out functionalityJameson Miller, Jun 28, 2018
  84. Junio C HamanoJun 28, 2018
  85. Jameson MillerJul 2, 2018
  86. 8/8 block alloc: add validations around cache_entry lifecyleJameson Miller, Jun 28, 2018
  87. 1/8 read-cache: teach refresh_cache_entry() to take istateJameson Miller, Jun 28, 2018
  88. 7/8 block alloc: allocate cache entries from mem-poolJameson Miller, Jun 28, 2018
  89. 0/8 Allocate cache entries from mem_poolJameson Miller, Jul 2, 2018
  90. 2/8 read-cache: teach make_cache_entry to take object_idJameson Miller, Jul 2, 2018
  91. Stefan BellerJul 2, 2018
  92. Jameson MillerJul 5, 2018
  93. 3/8 block alloc: add lifecycle APIs for cache_entry structsJameson Miller, Jul 2, 2018
  94. Duy NguyenJul 22, 2018
  95. 4/8 mem-pool: only search head block for available spaceJameson Miller, Jul 2, 2018
  96. 5/8 mem-pool: add life cycle management functionsJameson Miller, Jul 2, 2018
  97. 7/8 block alloc: allocate cache entries from mem_poolJameson Miller, Jul 2, 2018
  98. 8/8 block alloc: add validations around cache_entry lifecyleJameson Miller, Jul 2, 2018
  99. 6/8 mem-pool: fill out functionalityJameson Miller, Jul 2, 2018
  100. 1/8 read-cache: teach refresh_cache_entry to take istateJameson Miller, Jul 2, 2018

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