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add cache alignment directives for contended variables

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This commit is contained in:
daan 2020-01-24 19:02:13 -08:00
parent e070eba112
commit b31bc52618
6 changed files with 27 additions and 23 deletions
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26
src/segment.c
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@ -365,9 +365,6 @@ static void mi_reset_delayed(mi_segments_tld_t* tld) {
}
/* -----------------------------------------------------------
Segment size calculations
----------------------------------------------------------- */
@ -829,13 +826,15 @@ reuse their pages and/or free them eventually
We maintain a global list of abandoned segments that are
reclaimed on demand. Since this is shared among threads
the implementation needs to avoid the A-B-A problem on
popping abandoned segments which is why tagged pointers are
used.
popping abandoned segments: <https://en.wikipedia.org/wiki/ABA_problem>
We use tagged pointers to avoid accidentially identifying
reused segments, much like stamped references in Java.
Secondly, we maintain a reader counter to avoid resetting
or decommitting segments that have a pending read operation.
----------------------------------------------------------- */
// Use the bottom 20-bits (on 64-bit) of the aligned segment
// pointers to put in a tag that increments on update to avoid
// the A-B-A problem.
// Use the bottom 20-bits (on 64-bit) of the aligned segment pointers
// to put in a tag that increments on update to avoid the A-B-A problem.
#define MI_TAGGED_MASK MI_SEGMENT_MASK
typedef uintptr_t mi_tagged_segment_t;
@ -850,16 +849,17 @@ static mi_tagged_segment_t mi_tagged_segment(mi_segment_t* segment, mi_tagged_se
}
// This is a list of visited abandoned pages that were full at the time.
// this list migrates to `abandoned` when that becomes NULL.
static volatile _Atomic(mi_segment_t*) abandoned_visited; // = NULL
// this list migrates to `abandoned` when that becomes NULL. The use of
// this list reduces contention and the rate at which segments are visited.
static mi_decl_cache_align volatile _Atomic(mi_segment_t*) abandoned_visited; // = NULL
// The abandoned page list.
static volatile _Atomic(mi_tagged_segment_t) abandoned; // = NULL
// The abandoned page list (tagged as it supports pop)
static mi_decl_cache_align volatile _Atomic(mi_tagged_segment_t) abandoned; // = NULL
// We also maintain a count of current readers of the abandoned list
// in order to prevent resetting/decommitting segment memory if it might
// still be read.
static volatile _Atomic(uintptr_t) abandoned_readers; // = 0
static mi_decl_cache_align volatile _Atomic(uintptr_t) abandoned_readers; // = 0
// Push on the visited list
static void mi_abandoned_visited_push(mi_segment_t* segment) {