#ifndef JEMALLOC_INTERNAL_SC_H
#define JEMALLOC_INTERNAL_SC_H
#include "jemalloc/internal/jemalloc_internal_types.h"
/*
* Size class computations:
*
* These are a little tricky; we'll first start by describing how things
* generally work, and then describe some of the details.
*
* Ignore the first few size classes for a moment. We can then split all the
* remaining size classes into groups. The size classes in a group are spaced
* such that they cover allocation request sizes in a power-of-2 range. The
* power of two is called the base of the group, and the size classes in it
* satisfy allocations in the half-open range (base, base * 2]. There are
* SC_NGROUP size classes in each group, equally spaced in the range, so that
* each one covers allocations for base / SC_NGROUP possible allocation sizes.
* We call that value (base / SC_NGROUP) the delta of the group. Each size class
* is delta larger than the one before it (including the initial size class in a
* group, which is delta larger than base, the largest size class in the
* previous group).
* To make the math all work out nicely, we require that SC_NGROUP is a power of
* two, and define it in terms of SC_LG_NGROUP. We'll often talk in terms of
* lg_base and lg_delta. For each of these groups then, we have that
* lg_delta == lg_base - SC_LG_NGROUP.
* The size classes in a group with a given lg_base and lg_delta (which, recall,
* can be computed from lg_base for these groups) are therefore:
* base + 1 * delta
* which covers allocations in (base, base + 1 * delta]
* base + 2 * delta
* which covers allocations in (base + 1 * delta, base + 2 * delta].
* base + 3 * delta
* which covers allocations in (base + 2 * delta, base + 3 * delta].
* ...
* base + SC_NGROUP * delta ( == 2 * base)
* which covers allocations in (base + (SC_NGROUP - 1) * delta, 2 * base].
* (Note that currently SC_NGROUP is always 4, so the "..." is empty in
* practice.)
* Note that the last size class in the group is the next power of two (after
* base), so that we've set up the induction correctly for the next group's
* selection of delta.
*
* Now, let's start considering the first few size classes. Two extra constants
* come into play here: LG_QUANTUM and SC_LG_TINY_MIN. LG_QUANTUM ensures
* correct platform alignment; all objects of size (1 << LG_QUANTUM) or larger
* are at least (1 << LG_QUANTUM) aligned; this can be used to ensure that we
* never return improperly aligned memory, by making (1 << LG_QUANTUM) equal the
* highest required alignment of a platform. For allocation sizes smaller than
* (1 << LG_QUANTUM) though, we can be more relaxed (since we don't support
* platforms with types with alignment larger than their size). To allow such
* allocations (without wasting space unnecessarily), we introduce tiny size
* classes; one per power of two, up until we hit the quantum size. There are
* therefore LG_QUANTUM - SC_LG_TINY_MIN such size classes.
*
* Next, we have a size class of size (1 << LG_QUANTUM). This can't be the
* start of a group in the sense we described above (covering a power of two
* range) since, if we divided into it to pick a value of delta, we'd get a
* delta smaller than (1 << LG_QUANTUM) for sizes >= (1 << LG_QUANTUM), which
* is against the rules.
*
* The first base we can divide by SC_NGROUP while still being at least
* (1 << LG_QUANTUM) is SC_NGROUP * (1 << LG_QUANTUM). We can get there by
* having SC_NGROUP size classes, spaced (1 << LG_QUANTUM) apart. These size
* classes are:
* 1 * (1 << LG_QUANTUM)
* 2 * (1 << LG_QUANTUM)
* 3 * (1 << LG_QUANTUM)
* ... (although, as above, this "..." is empty in practice)
* SC_NGROUP * (1 << LG_QUANTUM).
*
* There are SC_NGROUP of these size classes, so we can regard it as a sort of
* pseudo-group, even though it spans multiple powers of 2, is divided
* differently, and both starts and ends on a power of 2 (as opposed to just
* ending). SC_NGROUP is itself a power of two, so the first group after the
* pseudo-group has the power-of-two base SC_NGROUP * (1 << LG_QUANTUM), for a
* lg_base of LG_QUANTUM + SC_LG_NGROUP. We can divide this base into SC_NGROUP
* sizes without violating our LG_QUANTUM requirements, so we can safely set
* lg_delta = lg_base - SC_LG_GROUP (== LG_QUANTUM).
*
* So, in order, the size classes are:
*
* Tiny size classes:
* - Count: LG_QUANTUM - SC_LG_TINY_MIN.
* - Sizes:
* 1 << SC_LG_TINY_MIN
* 1 << (SC_LG_TINY_MIN + 1)
* 1 << (SC_LG_TINY_MIN + 2)
* ...
* 1 << (LG_QUANTUM - 1)
*
* Initial pseudo-group:
* - Count: SC_NGROUP
* - Sizes:
* 1 * (1 << LG_QUANTUM)
* 2 * (1 << LG_QUANTUM)
* 3 * (1 << LG_QUANTUM)
* ...
* SC_NGROUP * (1 << LG_QUANTUM)
*
* Regular group 0:
* - Count: SC_NGROUP
* - Sizes:
* (relative to lg_base of LG_QUANTUM + SC_LG_NGROUP and lg_delta of
* lg_base - SC_LG_NGROUP)
* (1 << lg_base) + 1 * (1 << lg_delta)
* (1 << lg_base) + 2 * (1 << lg_delta)
* (1 << lg_base) + 3 * (1 << lg_delta)
* ...
* (1 << lg_base) + SC_NGROUP * (1 << lg_delta) [ == (1 << (lg_base + 1)) ]
*
* Regular group 1:
* - Count: SC_NGROUP
* - Sizes:
* (relative to lg_base of LG_QUANTUM + SC_LG_NGROUP + 1 and lg_delta of
* lg_base - SC_LG_NGROUP)
* (1 << lg_base) + 1 * (1 << lg_delta)
* (1 << lg_base) + 2 * (1 << lg_delta)
* (1 << lg_base) + 3 * (1 << lg_delta)
* ...
* (1 << lg_base) + SC_NGROUP * (1 << lg_delta) [ == (1 << (lg_base + 1)) ]
*
* ...
*
* Regular group N:
* - Count: SC_NGROUP
* - Sizes:
* (relative to lg_base of LG_QUANTUM + SC_LG_NGROUP + N and lg_delta of
* lg_base - SC_LG_NGROUP)
* (1 << lg_base) + 1 * (1 << lg_delta)
* (1 << lg_base) + 2 * (1 << lg_delta)
* (1 << lg_base) + 3 * (1 << lg_delta)
* ...
* (1 << lg_base) + SC_NGROUP * (1 << lg_delta) [ == (1 << (lg_base + 1)) ]
*
*
* Representation of metadata:
* To make the math easy, we'll mostly work in lg quantities. We record lg_base,
* lg_delta, and ndelta (i.e. number of deltas above the base) on a
* per-size-class basis, and maintain the invariant that, across all size
* classes, size == (1 << lg_base) + ndelta * (1 << lg_delta).
*
* For regular groups (i.e. those with lg_base >= LG_QUANTUM + SC_LG_NGROUP),
* lg_delta is lg_base - SC_LG_NGROUP, and ndelta goes from 1 to SC_NGROUP.
*
* For the initial tiny size classes (if any), lg_base is lg(size class size).
* lg_delta is lg_base for the first size class, and lg_base - 1 for all
* subsequent ones. ndelta is always 0.
*
* For the pseudo-group, if there are no tiny size classes, then we set
* lg_base == LG_QUANTUM, lg_delta == LG_QUANTUM, and have ndelta range from 0
* to SC_NGROUP - 1. (Note that delta == base, so base + (SC_NGROUP - 1) * delta
* is just SC_NGROUP * base, or (1 << (SC_LG_NGROUP + LG_QUANTUM)), so we do
* indeed get a power of two that way). If there *are* tiny size classes, then
* the first size class needs to have lg_delta relative to the largest tiny size
* class. We therefore set lg_base == LG_QUANTUM - 1,
* lg_delta == LG_QUANTUM - 1, and ndelta == 1, keeping the rest of the
* pseudo-group the same.
*
*
* Other terminology:
* "Small" size classes mean those that are allocated out of bins, which is the
* same as those that are slab allocated.
* "Large" size classes are those that are not small. The cutoff for counting as
* large is page size * group size.
*/
/*
* Size class N + (1 << SC_LG_NGROUP) twice the size of size class N.
*/
#define SC_LG_NGROUP 2
#define SC_LG_TINY_MIN 3
#if SC_LG_TINY_MIN == 0
/* The div module doesn't support division by 1, which this would require. */
#error "Unsupported LG_TINY_MIN"
#endif
/*
* The definitions below are all determined by the above settings and system
* characteristics.
*/
#define SC_NGROUP (1ULL << SC_LG_NGROUP)
#define SC_PTR_BITS ((1ULL << LG_SIZEOF_PTR) * 8)
#define SC_NTINY (LG_QUANTUM - SC_LG_TINY_MIN)
#define SC_LG_TINY_MAXCLASS (LG_QUANTUM > SC_LG_TINY_MIN ? LG_QUANTUM - 1 : -1)
#define SC_NPSEUDO SC_NGROUP
#define SC_LG_FIRST_REGULAR_BASE (LG_QUANTUM + SC_LG_NGROUP)
/*
* We cap allocations to be less than 2 ** (ptr_bits - 1), so the highest base
* we need is 2 ** (ptr_bits - 2). (This also means that the last group is 1
* size class shorter than the others).
* We could probably save some space in arenas by capping this at LG_VADDR size.
*/
#define SC_LG_BASE_MAX (SC_PTR_BITS - 2)
#define SC_NREGULAR (SC_NGROUP * \
(SC_LG_BASE_MAX - SC_LG_FIRST_REGULAR_BASE + 1) - 1)
#define SC_NSIZES (SC_NTINY + SC_NPSEUDO + SC_NREGULAR)
/* The number of size classes that are a multiple of the page size. */
#define SC_NPSIZES ( \
/* Start with all the size classes. */ \
SC_NSIZES \
/* Subtract out those groups with too small a base. */ \
- (LG_PAGE - 1 - SC_LG_FIRST_REGULAR_BASE) * SC_NGROUP \
/* And the pseudo-group. */ \
- SC_NPSEUDO \
/* And the tiny group. */ \
- SC_NTINY \
/* Sizes where ndelta*delta is not a multiple of the page size. */ \
- (SC_LG_NGROUP * SC_NGROUP))
/*
* Note that the last line is computed as the sum of the second column in the
* following table:
* lg(base) | count of sizes to exclude
* ------------------------------|-----------------------------
* LG_PAGE - 1 | SC_NGROUP - 1
* LG_PAGE | SC_NGROUP - 1
* LG_PAGE + 1 | SC_NGROUP - 2
* LG_PAGE + 2 | SC_NGROUP - 4
* ... | ...
* LG_PAGE + (SC_LG_NGROUP - 1) | SC_NGROUP - (SC_NGROUP / 2)
*/
/*
* We declare a size class is binnable if size < page size * group. Or, in other
* words, lg(size) < lg(page size) + lg(group size).
*/
#define SC_NBINS ( \
/* Sub-regular size classes. */ \
SC_NTINY + SC_NPSEUDO \
/* Groups with lg_regular_min_base <= lg_base <= lg_base_max */ \
+ SC_NGROUP * (LG_PAGE + SC_LG_NGROUP - SC_LG_FIRST_REGULAR_BASE) \
/* Last SC of the last group hits the bound exactly; exclude it. */ \
- 1)
/*
* The size2index_tab lookup table uses uint8_t to encode each bin index, so we
* cannot support more than 256 small size classes.
*/
#if (SC_NBINS > 256)
# error "Too many small size classes"
#endif
/* The largest size class in the lookup table. */
#define SC_LOOKUP_MAXCLASS ((size_t)1 << 12)
/* Internal, only used for the definition of SC_SMALL_MAXCLASS. */
#define SC_SMALL_MAX_BASE ((size_t)1 << (LG_PAGE + SC_LG_NGROUP - 1))
#define SC_SMALL_MAX_DELTA ((size_t)1 << (LG_PAGE - 1))
/* The largest size class allocated out of a slab. */
#define SC_SMALL_MAXCLASS (SC_SMALL_MAX_BASE \
+ (SC_NGROUP - 1) * SC_SMALL_MAX_DELTA)
/* The smallest size class not allocated out of a slab. */
#define SC_LARGE_MINCLASS ((size_t)1ULL << (LG_PAGE + SC_LG_NGROUP))
#define SC_LG_LARGE_MINCLASS (LG_PAGE + SC_LG_NGROUP)
/* Internal; only used for the definition of SC_LARGE_MAXCLASS. */
#define SC_MAX_BASE ((size_t)1 << (SC_PTR_BITS - 2))
#define SC_MAX_DELTA ((size_t)1 << (SC_PTR_BITS - 2 - SC_LG_NGROUP))
/* The largest size class supported. */
#define SC_LARGE_MAXCLASS (SC_MAX_BASE + (SC_NGROUP - 1) * SC_MAX_DELTA)
typedef struct sc_s sc_t;
struct sc_s {
/* Size class index, or -1 if not a valid size class. */
int index;
/* Lg group base size (no deltas added). */
int lg_base;
/* Lg delta to previous size class. */
int lg_delta;
/* Delta multiplier. size == 1<