Use fixed point integer math instead of floating point math when
calculating run sizes. Use of the floating point unit was a potential pessimization to context switching for applications that do not otherwise use floating point math. [1] Reformat cpp macro-related comments to improve consistency. Submitted by: das
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jasone
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@ -101,7 +101,14 @@
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/* #define MALLOC_PRODUCTION */
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#ifndef MALLOC_PRODUCTION
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/*
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* MALLOC_DEBUG enables assertions and other sanity checks, and disables
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* inline functions.
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*/
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# define MALLOC_DEBUG
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/* MALLOC_STATS enables statistics calculation. */
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# define MALLOC_STATS
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#endif
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/*
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@ -156,11 +163,6 @@ __FBSDID("$FreeBSD$");
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#include "un-namespace.h"
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/* MALLOC_STATS enables statistics calculation. */
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#ifndef MALLOC_PRODUCTION
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# define MALLOC_STATS
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#endif
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#ifdef MALLOC_DEBUG
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# ifdef NDEBUG
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# undef NDEBUG
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@ -267,35 +269,40 @@ __FBSDID("$FreeBSD$");
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#define SMALL_MAX_DEFAULT (1U << SMALL_MAX_2POW_DEFAULT)
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/*
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* Maximum desired run header overhead. Runs are sized as small as possible
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* such that this setting is still honored, without violating other constraints.
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* The goal is to make runs as small as possible without exceeding a per run
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* external fragmentation threshold.
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* RUN_MAX_OVRHD indicates maximum desired run header overhead. Runs are sized
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* as small as possible such that this setting is still honored, without
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* violating other constraints. The goal is to make runs as small as possible
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* without exceeding a per run external fragmentation threshold.
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*
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* Note that it is possible to set this low enough that it cannot be honored
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* for some/all object sizes, since there is one bit of header overhead per
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* object (plus a constant). In such cases, this constraint is relaxed.
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* We use binary fixed point math for overhead computations, where the binary
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* point is implicitly RUN_BFP bits to the left.
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*
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* RUN_MAX_OVRHD_RELAX specifies the maximum number of bits per region of
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* overhead for which RUN_MAX_OVRHD is relaxed.
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* Note that it is possible to set RUN_MAX_OVRHD low enough that it cannot be
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* honored for some/all object sizes, since there is one bit of header overhead
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* per object (plus a constant). This constraint is relaxed (ignored) for runs
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* that are so small that the per-region overhead is greater than:
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*
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* (RUN_MAX_OVRHD / (reg_size << (3+RUN_BFP))
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*/
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#define RUN_MAX_OVRHD 0.015
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#define RUN_MAX_OVRHD_RELAX 1.5
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#define RUN_BFP 12
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/* \/ Implicit binary fixed point. */
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#define RUN_MAX_OVRHD 0x0000003dU
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#define RUN_MAX_OVRHD_RELAX 0x00001800U
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/* Put a cap on small object run size. This overrides RUN_MAX_OVRHD. */
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#define RUN_MAX_SMALL_2POW 15
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#define RUN_MAX_SMALL (1U << RUN_MAX_SMALL_2POW)
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#ifdef MALLOC_LAZY_FREE
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/* Default size of each arena's lazy free cache. */
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# define LAZY_FREE_2POW_DEFAULT 8
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/*
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* Number of pseudo-random probes to conduct before considering the cache to be
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* overly full. It takes on average n probes to detect fullness of (n-1)/n.
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* However, we are effectively doing multiple non-independent trials (each
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* deallocation is a trial), so the actual average threshold for clearing the
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* cache is somewhat lower.
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*/
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/* Default size of each arena's lazy free cache. */
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# define LAZY_FREE_2POW_DEFAULT 8
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/*
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* Number of pseudo-random probes to conduct before considering the cache to
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* be overly full. It takes on average n probes to detect fullness of
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* (n-1)/n. However, we are effectively doing multiple non-independent
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* trials (each deallocation is a trial), so the actual average threshold
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* for clearing the cache is somewhat lower.
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*/
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# define LAZY_FREE_NPROBES 5
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#endif
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@ -323,20 +330,20 @@ __FBSDID("$FreeBSD$");
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#define BLOCK_COST_2POW 4
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#ifdef MALLOC_BALANCE
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/*
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* We use an exponential moving average to track recent lock contention, where
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* the size of the history window is N, and alpha=2/(N+1).
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*
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* Due to integer math rounding, very small values here can cause substantial
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* degradation in accuracy, thus making the moving average decay faster than it
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* would with precise calculation.
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*/
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/*
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* We use an exponential moving average to track recent lock contention,
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* where the size of the history window is N, and alpha=2/(N+1).
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*
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* Due to integer math rounding, very small values here can cause
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* substantial degradation in accuracy, thus making the moving average decay
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* faster than it would with precise calculation.
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*/
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# define BALANCE_ALPHA_INV_2POW 9
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/*
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* Threshold value for the exponential moving contention average at which to
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* re-assign a thread.
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*/
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/*
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* Threshold value for the exponential moving contention average at which to
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* re-assign a thread.
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*/
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# define BALANCE_THRESHOLD_DEFAULT (1U << (SPIN_LIMIT_2POW-4))
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#endif
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@ -2468,7 +2475,6 @@ arena_bin_run_size_calc(arena_bin_t *bin, size_t min_run_size)
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size_t try_run_size, good_run_size;
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unsigned good_nregs, good_mask_nelms, good_reg0_offset;
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unsigned try_nregs, try_mask_nelms, try_reg0_offset;
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float max_ovrhd = RUN_MAX_OVRHD;
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assert(min_run_size >= pagesize);
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assert(min_run_size <= arena_maxclass);
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@ -2486,7 +2492,7 @@ arena_bin_run_size_calc(arena_bin_t *bin, size_t min_run_size)
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*/
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try_run_size = min_run_size;
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try_nregs = ((try_run_size - sizeof(arena_run_t)) / bin->reg_size)
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+ 1; /* Counter-act the first line of the loop. */
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+ 1; /* Counter-act try_nregs-- in loop. */
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do {
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try_nregs--;
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try_mask_nelms = (try_nregs >> (SIZEOF_INT_2POW + 3)) +
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@ -2519,9 +2525,8 @@ arena_bin_run_size_calc(arena_bin_t *bin, size_t min_run_size)
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} while (sizeof(arena_run_t) + (sizeof(unsigned) *
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(try_mask_nelms - 1)) > try_reg0_offset);
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} while (try_run_size <= arena_maxclass && try_run_size <= RUN_MAX_SMALL
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&& max_ovrhd > RUN_MAX_OVRHD_RELAX / ((float)(bin->reg_size << 3))
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&& ((float)(try_reg0_offset)) / ((float)(try_run_size)) >
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max_ovrhd);
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&& RUN_MAX_OVRHD * (bin->reg_size << 3) > RUN_MAX_OVRHD_RELAX
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&& (try_reg0_offset << RUN_BFP) > RUN_MAX_OVRHD * try_run_size);
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assert(sizeof(arena_run_t) + (sizeof(unsigned) * (good_mask_nelms - 1))
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<= good_reg0_offset);
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