hphp/runtime/base/purger.h

   1 /*
   2    +----------------------------------------------------------------------+
   3    | HipHop for PHP                                                       |
   4    +----------------------------------------------------------------------+
   5    | Copyright (c) 2010-present Facebook, Inc. (http://www.facebook.com)  |
   6    +----------------------------------------------------------------------+
   7    | This source file is subject to version 3.01 of the PHP license,      |
   8    | that is bundled with this package in the file LICENSE, and is        |
   9    | available through the world-wide-web at the following url:           |
  10    | http://www.php.net/license/3_01.txt                                  |
  11    | If you did not receive a copy of the PHP license and are unable to   |
  12    | obtain it through the world-wide-web, please send a note to          |
  13    | license@php.net so we can mail you a copy immediately.               |
  14    +----------------------------------------------------------------------+
  15 */
  16
  17 #ifndef incl_HPHP_PURGER_H_
  18 #define incl_HPHP_PURGER_H_
  19
  20 #include <array>
  21 #include <cstddef>
  22 #include <cstdint>
  23
  24 namespace HPHP {
  25
  26 /*
  27  * Purger implements decay-based purging of unused dirty pages using a similar
  28  * algorithm to jemalloc. we maintain a number of buckets, representing time
  29  * slices over the decay time window. Each bucket tracks the max heap size
  30  * observed in that time slice.
  31  *
  32  * Each time purge() is called, we apply the decay function to the heap size for
  33  * each slice, to arrive at the number of unused dirty pages we would like to
  34  * retain, then purge the rest by calling madvise(MADV_DONTNEED).
  35  *
  36  * There are a few tuning parameters in Purger:
  37  * kNumBuckets: 16,     the number of time slices over the decay time window
  38  * RuntimeOption::HeapPurgeThreshold: (bytes) max retained dirty memory
  39  *   anything over this is eagerly purged. default 128MB.
  40  * RuntimeOption::HeapPurgeWindowSize: (ns) decay time window. default 5s.
  41  */
  42
  43 struct Purger {
  44   Purger();
  45
  46   /*
  47    * Purge the memory from base to front, according to the decay curve
  48    */
  49   void purge(char* base, char* front);
  50
  51   /*
  52    * Purge all the dirty pages starting from base
  53    */
  54   void flush(char* base);
  55
  56 private:
  57   static const int64_t kNumBuckets = 16;
  58   struct Bucket {
  59     int64_t time; // most recent timestamp for this bucket
  60     size_t max;   // max heap size in this bucket time slice
  61   };
  62
  63   // Time window size for purge size calculation. The amount of memory that
  64   // is allowed to be alive will be set to the maximum memory amount of the
  65   // latest time window according to the decay curve.
  66   int64_t const window_;
  67
  68   // the dirty_ memory threshold
  69   size_t const threshold_;
  70   int64_t const bucket_slice_;
  71   size_t dirty_; // bytes of dirty memory
  72   std::array<Bucket,kNumBuckets> buckets_; // buckets array for time window
  73   int const id_;
  74 };
  75
  76 }
  77
  78 #endif