From eaaa368bab472a78e99a25c1641d24ad3c2283ad Mon Sep 17 00:00:00 2001 From: Charles Date: Tue, 1 Feb 2022 20:26:39 +0800 Subject: [PATCH] Add comments and use meaningful vars in sz_psz2ind. --- Makefile.in | 1 + include/jemalloc/internal/sc.h | 1 + include/jemalloc/internal/sz.h | 48 ++++++++++++++++++++----- src/sc.c | 2 +- test/unit/sz.c | 66 ++++++++++++++++++++++++++++++++++ 5 files changed, 108 insertions(+), 10 deletions(-) create mode 100644 test/unit/sz.c diff --git a/Makefile.in b/Makefile.in index 8e16982e..cf6d5687 100644 --- a/Makefile.in +++ b/Makefile.in @@ -278,6 +278,7 @@ TESTS_UNIT := \ $(srcroot)test/unit/spin.c \ $(srcroot)test/unit/stats.c \ $(srcroot)test/unit/stats_print.c \ + $(srcroot)test/unit/sz.c \ $(srcroot)test/unit/tcache_max.c \ $(srcroot)test/unit/test_hooks.c \ $(srcroot)test/unit/thread_event.c \ diff --git a/include/jemalloc/internal/sc.h b/include/jemalloc/internal/sc.h index 8efd3249..308985fa 100644 --- a/include/jemalloc/internal/sc.h +++ b/include/jemalloc/internal/sc.h @@ -344,6 +344,7 @@ struct sc_data_s { sc_t sc[SC_NSIZES]; }; +size_t reg_size_compute(int lg_base, int lg_delta, int ndelta); void sc_data_init(sc_data_t *data); /* * Updates slab sizes in [begin, end] to be pgs pages in length, if possible. diff --git a/include/jemalloc/internal/sz.h b/include/jemalloc/internal/sz.h index f2be6139..3c0fc1da 100644 --- a/include/jemalloc/internal/sz.h +++ b/include/jemalloc/internal/sz.h @@ -55,22 +55,52 @@ extern void sz_boot(const sc_data_t *sc_data, bool cache_oblivious); JEMALLOC_ALWAYS_INLINE pszind_t sz_psz2ind(size_t psz) { + assert(psz > 0); if (unlikely(psz > SC_LARGE_MAXCLASS)) { return SC_NPSIZES; } - pszind_t x = lg_floor((psz<<1)-1); - pszind_t shift = (x < SC_LG_NGROUP + LG_PAGE) ? + /* x is the lg of the first base >= psz. */ + pszind_t x = lg_ceil(psz); + /* + * sc.h introduces a lot of size classes. These size classes are divided + * into different size class groups. There is a very special size class + * group, each size class in or after it is an integer multiple of PAGE. + * We call it first_ps_rg. It means first page size regular group. The + * range of first_ps_rg is (base, base * 2], and base == PAGE * + * SC_NGROUP. off_to_first_ps_rg begins from 1, instead of 0. e.g. + * off_to_first_ps_rg is 1 when psz is (PAGE * SC_NGROUP + 1). + */ + pszind_t off_to_first_ps_rg = (x < SC_LG_NGROUP + LG_PAGE) ? 0 : x - (SC_LG_NGROUP + LG_PAGE); - pszind_t grp = shift << SC_LG_NGROUP; - pszind_t lg_delta = (x < SC_LG_NGROUP + LG_PAGE + 1) ? - LG_PAGE : x - SC_LG_NGROUP - 1; + /* + * Same as sc_s::lg_delta. + * Delta for off_to_first_ps_rg == 1 is PAGE, + * for each increase in offset, it's multiplied by two. + * Therefore, lg_delta = LG_PAGE + (off_to_first_ps_rg - 1). + */ + pszind_t lg_delta = (off_to_first_ps_rg == 0) ? + LG_PAGE : LG_PAGE + (off_to_first_ps_rg - 1); - size_t delta_inverse_mask = ZU(-1) << lg_delta; - pszind_t mod = ((((psz-1) & delta_inverse_mask) >> lg_delta)) & - ((ZU(1) << SC_LG_NGROUP) - 1); + /* + * Let's write psz in binary, e.g. 0011 for 0x3, 0111 for 0x7. + * The leftmost bits whose len is lg_base decide the base of psz. + * The rightmost bits whose len is lg_delta decide (pgz % PAGE). + * The middle bits whose len is SC_LG_NGROUP decide ndelta. + * ndelta is offset to the first size class in the size class group, + * starts from 1. + * If you don't know lg_base, ndelta or lg_delta, see sc.h. + * |xxxxxxxxxxxxxxxxxxxx|------------------------|yyyyyyyyyyyyyyyyyyyyy| + * |<-- len: lg_base -->|<-- len: SC_LG_NGROUP-->|<-- len: lg_delta -->| + * |<-- ndelta -->| + * rg_inner_off = ndelta - 1 + * Why use (psz - 1)? + * To handle case: psz % (1 << lg_delta) == 0. + */ + pszind_t rg_inner_off = (((psz - 1)) >> lg_delta) & (SC_NGROUP - 1); - pszind_t ind = grp + mod; + pszind_t base_ind = off_to_first_ps_rg << SC_LG_NGROUP; + pszind_t ind = base_ind + rg_inner_off; return ind; } diff --git a/src/sc.c b/src/sc.c index 9a0f76d5..e4a94d89 100644 --- a/src/sc.c +++ b/src/sc.c @@ -13,7 +13,7 @@ * at least the damage is compartmentalized to this file. */ -static size_t +size_t reg_size_compute(int lg_base, int lg_delta, int ndelta) { return (ZU(1) << lg_base) + (ZU(ndelta) << lg_delta); } diff --git a/test/unit/sz.c b/test/unit/sz.c new file mode 100644 index 00000000..be11aca4 --- /dev/null +++ b/test/unit/sz.c @@ -0,0 +1,66 @@ +#include "test/jemalloc_test.h" + +TEST_BEGIN(test_sz_psz2ind) { + /* + * Testing page size classes which reside prior to the regular group + * with all size classes divisible by page size. + * For x86_64 Linux, it's 4096, 8192, 12288, 16384, with correponding + * pszind 0, 1, 2 and 3. + */ + for (size_t i = 0; i < SC_NGROUP; i++) { + for (size_t psz = i * PAGE + 1; psz <= (i + 1) * PAGE; psz++) { + pszind_t ind = sz_psz2ind(psz); + expect_zu_eq(ind, i, "Got %u as sz_psz2ind of %zu", ind, + psz); + } + } + + sc_data_t data; + memset(&data, 0, sizeof(data)); + sc_data_init(&data); + /* + * 'base' is the base of the first regular group with all size classes + * divisible by page size. + * For x86_64 Linux, it's 16384, and base_ind is 36. + */ + size_t base_psz = 1 << (SC_LG_NGROUP + LG_PAGE); + size_t base_ind = 0; + while (base_ind < SC_NSIZES && + reg_size_compute(data.sc[base_ind].lg_base, + data.sc[base_ind].lg_delta, + data.sc[base_ind].ndelta) < base_psz) { + base_ind++; + } + expect_zu_eq( + reg_size_compute(data.sc[base_ind].lg_base, + data.sc[base_ind].lg_delta, data.sc[base_ind].ndelta), + base_psz, "Size class equal to %zu not found", base_psz); + /* + * Test different sizes falling into groups after the 'base'. The + * increment is PAGE / 3 for the execution speed purpose. + */ + base_ind -= SC_NGROUP; + for (size_t psz = base_psz; psz <= 64 * 1024 * 1024; psz += PAGE / 3) { + pszind_t ind = sz_psz2ind(psz); + sc_t gt_sc = data.sc[ind + base_ind]; + expect_zu_gt(psz, + reg_size_compute(gt_sc.lg_base, gt_sc.lg_delta, + gt_sc.ndelta), + "Got %u as sz_psz2ind of %zu", ind, psz); + sc_t le_sc = data.sc[ind + base_ind + 1]; + expect_zu_le(psz, + reg_size_compute(le_sc.lg_base, le_sc.lg_delta, + le_sc.ndelta), + "Got %u as sz_psz2ind of %zu", ind, psz); + } + + pszind_t max_ind = sz_psz2ind(SC_LARGE_MAXCLASS + 1); + expect_lu_eq(max_ind, SC_NPSIZES, + "Got %u as sz_psz2ind of %llu", max_ind, SC_LARGE_MAXCLASS); +} +TEST_END + +int +main(void) { + return test(test_sz_psz2ind); +}