server-skynet-source-3rd-je.../src/sc.c
Dave Watson d1a861fa80 add a check for SC_LARGE_MAXCLASS
If we assume SC_LARGE_MAXCLASS will always fit in a SSIZE_T, then we can
optimize some checks by unconditional subtraction, and then checking flags
only, without a compare statement in x86.
2018-10-15 08:24:12 -07:00

314 lines
8.2 KiB
C

#include "jemalloc/internal/jemalloc_preamble.h"
#include "jemalloc/internal/assert.h"
#include "jemalloc/internal/bit_util.h"
#include "jemalloc/internal/bitmap.h"
#include "jemalloc/internal/pages.h"
#include "jemalloc/internal/sc.h"
/*
* This module computes the size classes used to satisfy allocations. The logic
* here was ported more or less line-by-line from a shell script, and because of
* that is not the most idiomatic C. Eventually we should fix this, but for now
* at least the damage is compartmentalized to this file.
*/
sc_data_t sc_data_global;
static size_t
reg_size_compute(int lg_base, int lg_delta, int ndelta) {
return (ZU(1) << lg_base) + (ZU(ndelta) << lg_delta);
}
/* Returns the number of pages in the slab. */
static int
slab_size(int lg_page, int lg_base, int lg_delta, int ndelta) {
size_t page = (ZU(1) << lg_page);
size_t reg_size = reg_size_compute(lg_base, lg_delta, ndelta);
size_t try_slab_size = page;
size_t try_nregs = try_slab_size / reg_size;
size_t perfect_slab_size = 0;
bool perfect = false;
/*
* This loop continues until we find the least common multiple of the
* page size and size class size. Size classes are all of the form
* base + ndelta * delta == (ndelta + base/ndelta) * delta, which is
* (ndelta + ngroup) * delta. The way we choose slabbing strategies
* means that delta is at most the page size and ndelta < ngroup. So
* the loop executes for at most 2 * ngroup - 1 iterations, which is
* also the bound on the number of pages in a slab chosen by default.
* With the current default settings, this is at most 7.
*/
while (!perfect) {
perfect_slab_size = try_slab_size;
size_t perfect_nregs = try_nregs;
try_slab_size += page;
try_nregs = try_slab_size / reg_size;
if (perfect_slab_size == perfect_nregs * reg_size) {
perfect = true;
}
}
return (int)(perfect_slab_size / page);
}
static void
size_class(
/* Output. */
sc_t *sc,
/* Configuration decisions. */
int lg_max_lookup, int lg_page, int lg_ngroup,
/* Inputs specific to the size class. */
int index, int lg_base, int lg_delta, int ndelta) {
sc->index = index;
sc->lg_base = lg_base;
sc->lg_delta = lg_delta;
sc->ndelta = ndelta;
sc->psz = (reg_size_compute(lg_base, lg_delta, ndelta)
% (ZU(1) << lg_page) == 0);
size_t size = (ZU(1) << lg_base) + (ZU(ndelta) << lg_delta);
if (index == 0) {
assert(!sc->psz);
}
if (size < (ZU(1) << (lg_page + lg_ngroup))) {
sc->bin = true;
sc->pgs = slab_size(lg_page, lg_base, lg_delta, ndelta);
} else {
sc->bin = false;
sc->pgs = 0;
}
if (size <= (ZU(1) << lg_max_lookup)) {
sc->lg_delta_lookup = lg_delta;
} else {
sc->lg_delta_lookup = 0;
}
}
static void
size_classes(
/* Output. */
sc_data_t *sc_data,
/* Determined by the system. */
size_t lg_ptr_size, int lg_quantum,
/* Configuration decisions. */
int lg_tiny_min, int lg_max_lookup, int lg_page, int lg_ngroup) {
int ptr_bits = (1 << lg_ptr_size) * 8;
int ngroup = (1 << lg_ngroup);
int ntiny = 0;
int nlbins = 0;
int lg_tiny_maxclass = (unsigned)-1;
int nbins = 0;
int npsizes = 0;
int index = 0;
int ndelta = 0;
int lg_base = lg_tiny_min;
int lg_delta = lg_base;
/* Outputs that we update as we go. */
size_t lookup_maxclass = 0;
size_t small_maxclass = 0;
int lg_large_minclass = 0;
size_t large_maxclass = 0;
/* Tiny size classes. */
while (lg_base < lg_quantum) {
sc_t *sc = &sc_data->sc[index];
size_class(sc, lg_max_lookup, lg_page, lg_ngroup, index,
lg_base, lg_delta, ndelta);
if (sc->lg_delta_lookup != 0) {
nlbins = index + 1;
}
if (sc->psz) {
npsizes++;
}
if (sc->bin) {
nbins++;
}
ntiny++;
/* Final written value is correct. */
lg_tiny_maxclass = lg_base;
index++;
lg_delta = lg_base;
lg_base++;
}
/* First non-tiny (pseudo) group. */
if (ntiny != 0) {
sc_t *sc = &sc_data->sc[index];
/*
* See the note in sc.h; the first non-tiny size class has an
* unusual encoding.
*/
lg_base--;
ndelta = 1;
size_class(sc, lg_max_lookup, lg_page, lg_ngroup, index,
lg_base, lg_delta, ndelta);
index++;
lg_base++;
lg_delta++;
if (sc->psz) {
npsizes++;
}
if (sc->bin) {
nbins++;
}
}
while (ndelta < ngroup) {
sc_t *sc = &sc_data->sc[index];
size_class(sc, lg_max_lookup, lg_page, lg_ngroup, index,
lg_base, lg_delta, ndelta);
index++;
ndelta++;
if (sc->psz) {
npsizes++;
}
if (sc->bin) {
nbins++;
}
}
/* All remaining groups. */
lg_base = lg_base + lg_ngroup;
while (lg_base < ptr_bits - 1) {
ndelta = 1;
int ndelta_limit;
if (lg_base == ptr_bits - 2) {
ndelta_limit = ngroup - 1;
} else {
ndelta_limit = ngroup;
}
while (ndelta <= ndelta_limit) {
sc_t *sc = &sc_data->sc[index];
size_class(sc, lg_max_lookup, lg_page, lg_ngroup, index,
lg_base, lg_delta, ndelta);
if (sc->lg_delta_lookup != 0) {
nlbins = index + 1;
/* Final written value is correct. */
lookup_maxclass = (ZU(1) << lg_base)
+ (ZU(ndelta) << lg_delta);
}
if (sc->psz) {
npsizes++;
}
if (sc->bin) {
nbins++;
/* Final written value is correct. */
small_maxclass = (ZU(1) << lg_base)
+ (ZU(ndelta) << lg_delta);
if (lg_ngroup > 0) {
lg_large_minclass = lg_base + 1;
} else {
lg_large_minclass = lg_base + 2;
}
}
large_maxclass = (ZU(1) << lg_base)
+ (ZU(ndelta) << lg_delta);
index++;
ndelta++;
}
lg_base++;
lg_delta++;
}
/* Additional outputs. */
int nsizes = index;
unsigned lg_ceil_nsizes = lg_ceil(nsizes);
/* Fill in the output data. */
sc_data->ntiny = ntiny;
sc_data->nlbins = nlbins;
sc_data->nbins = nbins;
sc_data->nsizes = nsizes;
sc_data->lg_ceil_nsizes = lg_ceil_nsizes;
sc_data->npsizes = npsizes;
sc_data->lg_tiny_maxclass = lg_tiny_maxclass;
sc_data->lookup_maxclass = lookup_maxclass;
sc_data->small_maxclass = small_maxclass;
sc_data->lg_large_minclass = lg_large_minclass;
sc_data->large_minclass = (ZU(1) << lg_large_minclass);
sc_data->large_maxclass = large_maxclass;
/*
* We compute these values in two ways:
* - Incrementally, as above.
* - In macros, in sc.h.
* The computation is easier when done incrementally, but putting it in
* a constant makes it available to the fast paths without having to
* touch the extra global cacheline. We assert, however, that the two
* computations are equivalent.
*/
assert(sc_data->npsizes == SC_NPSIZES);
assert(sc_data->lg_tiny_maxclass == SC_LG_TINY_MAXCLASS);
assert(sc_data->small_maxclass == SC_SMALL_MAXCLASS);
assert(sc_data->large_minclass == SC_LARGE_MINCLASS);
assert(sc_data->lg_large_minclass == SC_LG_LARGE_MINCLASS);
assert(sc_data->large_maxclass == SC_LARGE_MAXCLASS);
/*
* In the allocation fastpath, we want to assume that we can
* unconditionally subtract the requested allocation size from
* a ssize_t, and detect passing through 0 correctly. This
* results in optimal generated code. For this to work, the
* maximum allocation size must be less than SSIZE_MAX.
*/
assert(SC_LARGE_MAXCLASS < SSIZE_MAX);
}
void
sc_data_init(sc_data_t *sc_data) {
assert(!sc_data->initialized);
int lg_max_lookup = 12;
size_classes(sc_data, LG_SIZEOF_PTR, LG_QUANTUM, SC_LG_TINY_MIN,
lg_max_lookup, LG_PAGE, 2);
sc_data->initialized = true;
}
static void
sc_data_update_sc_slab_size(sc_t *sc, size_t reg_size, size_t pgs_guess) {
size_t min_pgs = reg_size / PAGE;
if (reg_size % PAGE != 0) {
min_pgs++;
}
/*
* BITMAP_MAXBITS is actually determined by putting the smallest
* possible size-class on one page, so this can never be 0.
*/
size_t max_pgs = BITMAP_MAXBITS * reg_size / PAGE;
assert(min_pgs <= max_pgs);
assert(min_pgs > 0);
assert(max_pgs >= 1);
if (pgs_guess < min_pgs) {
sc->pgs = (int)min_pgs;
} else if (pgs_guess > max_pgs) {
sc->pgs = (int)max_pgs;
} else {
sc->pgs = (int)pgs_guess;
}
}
void
sc_data_update_slab_size(sc_data_t *data, size_t begin, size_t end, int pgs) {
assert(data->initialized);
for (int i = 0; i < data->nsizes; i++) {
sc_t *sc = &data->sc[i];
if (!sc->bin) {
break;
}
size_t reg_size = reg_size_compute(sc->lg_base, sc->lg_delta,
sc->ndelta);
if (begin <= reg_size && reg_size <= end) {
sc_data_update_sc_slab_size(sc, reg_size, pgs);
}
}
}
void
sc_boot(sc_data_t *data) {
sc_data_init(data);
}