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| author | Jason Evans <jasone@canonware.com> | 2017-05-16 20:25:17 (GMT) |
|---|---|---|
| committer | Jason Evans <jasone@canonware.com> | 2017-05-23 22:31:29 (GMT) |
| commit | 196a53c2aec9fd9fbd17af6803d75c7f631c1ae3 (patch) | |
| tree | 9a1fa9424562269a4d361b58f09de057a814eae6 /src/extent_dss.c | |
| parent | 067b97013018211b39e9911ae528ff54edd8fe5e (diff) | |
| download | jemalloc-196a53c2aec9fd9fbd17af6803d75c7f631c1ae3.zip jemalloc-196a53c2aec9fd9fbd17af6803d75c7f631c1ae3.tar.gz jemalloc-196a53c2aec9fd9fbd17af6803d75c7f631c1ae3.tar.bz2 | |
Do not assume dss never decreases.
An sbrk() caller outside jemalloc can decrease the dss, so add a
separate atomic boolean to explicitly track whether jemalloc is
concurrently calling sbrk(), rather than depending on state outside
jemalloc's full control.
This resolves #802.
Diffstat (limited to 'src/extent_dss.c')
| -rw-r--r-- | src/extent_dss.c | 72 |
1 files changed, 34 insertions, 38 deletions
diff --git a/src/extent_dss.c b/src/extent_dss.c index 6b5d066..8e0ca65 100644 --- a/src/extent_dss.c +++ b/src/extent_dss.c @@ -28,6 +28,8 @@ static atomic_u_t dss_prec_default = ATOMIC_INIT( /* Base address of the DSS. */ static void *dss_base; +/* Atomic boolean indicating whether a thread is currently extending DSS. */ +static atomic_b_t dss_extending; /* Atomic boolean indicating whether the DSS is exhausted. */ static atomic_b_t dss_exhausted; /* Atomic current upper limit on DSS addresses. */ @@ -65,37 +67,41 @@ extent_dss_prec_set(dss_prec_t dss_prec) { return false; } +static void +extent_dss_extending_start(void) { + spin_t spinner = SPIN_INITIALIZER; + while (true) { + bool expected = false; + if (atomic_compare_exchange_weak_b(&dss_extending, &expected, + true, ATOMIC_ACQ_REL, ATOMIC_RELAXED)) { + break; + } + spin_adaptive(&spinner); + } +} + +static void +extent_dss_extending_finish(void) { + assert(atomic_load_b(&dss_extending, ATOMIC_RELAXED)); + + atomic_store_b(&dss_extending, false, ATOMIC_RELEASE); +} + static void * extent_dss_max_update(void *new_addr) { - void *max_cur; - /* * Get the current end of the DSS as max_cur and assure that dss_max is * up to date. */ - spin_t spinner = SPIN_INITIALIZER; - while (true) { - void *max_prev = atomic_load_p(&dss_max, ATOMIC_RELAXED); - - max_cur = extent_dss_sbrk(0); - if ((uintptr_t)max_prev > (uintptr_t)max_cur) { - /* - * Another thread optimistically updated dss_max. Wait - * for it to finish. - */ - spin_adaptive(&spinner); - continue; - } - if (atomic_compare_exchange_weak_p(&dss_max, &max_prev, - max_cur, ATOMIC_ACQ_REL, ATOMIC_RELAXED)) { - break; - } + void *max_cur = extent_dss_sbrk(0); + if (max_cur == (void *)-1) { + return NULL; } + atomic_store_p(&dss_max, max_cur, ATOMIC_RELEASE); /* Fixed new_addr can only be supported if it is at the edge of DSS. */ if (new_addr != NULL && max_cur != new_addr) { return NULL; } - return max_cur; } @@ -121,6 +127,7 @@ extent_alloc_dss(tsdn_t *tsdn, arena_t *arena, void *new_addr, size_t size, return NULL; } + extent_dss_extending_start(); if (!atomic_load_b(&dss_exhausted, ATOMIC_ACQUIRE)) { /* * The loop is necessary to recover from races with other @@ -168,21 +175,14 @@ extent_alloc_dss(tsdn_t *tsdn, arena_t *arena, void *new_addr, size_t size, assert((uintptr_t)max_cur + incr == (uintptr_t)ret + size); - /* - * Optimistically update dss_max, and roll back below if - * sbrk() fails. No other thread will try to extend the - * DSS while dss_max is greater than the current DSS - * max reported by sbrk(0). - */ - if (!atomic_compare_exchange_weak_p(&dss_max, &max_cur, - dss_next, ATOMIC_ACQ_REL, ATOMIC_RELAXED)) { - continue; - } - /* Try to allocate. */ void *dss_prev = extent_dss_sbrk(incr); if (dss_prev == max_cur) { /* Success. */ + atomic_store_p(&dss_max, dss_next, + ATOMIC_RELEASE); + extent_dss_extending_finish(); + if (gap_size_page != 0) { extent_dalloc_gap(tsdn, arena, gap); } else { @@ -209,14 +209,8 @@ extent_alloc_dss(tsdn_t *tsdn, arena_t *arena, void *new_addr, size_t size, } /* * Failure, whether due to OOM or a race with a raw - * sbrk() call from outside the allocator. Try to roll - * back optimistic dss_max update; if rollback fails, - * it's due to another caller of this function having - * succeeded since this invocation started, in which - * case rollback is not necessary. + * sbrk() call from outside the allocator. */ - atomic_compare_exchange_strong_p(&dss_max, &dss_next, - max_cur, ATOMIC_ACQ_REL, ATOMIC_RELAXED); if (dss_prev == (void *)-1) { /* OOM. */ atomic_store_b(&dss_exhausted, true, @@ -226,6 +220,7 @@ extent_alloc_dss(tsdn_t *tsdn, arena_t *arena, void *new_addr, size_t size, } } label_oom: + extent_dss_extending_finish(); extent_dalloc(tsdn, arena, gap); return NULL; } @@ -265,6 +260,7 @@ extent_dss_boot(void) { cassert(have_dss); dss_base = extent_dss_sbrk(0); + atomic_store_b(&dss_extending, false, ATOMIC_RELAXED); atomic_store_b(&dss_exhausted, dss_base == (void *)-1, ATOMIC_RELAXED); atomic_store_p(&dss_max, dss_base, ATOMIC_RELAXED); } |