Updates to tcache

* remove legacy environment variables
* remove tcache mallopt() options
* tweak size2tidx/tidx2size macros to be more accurate and consistent
* add comments
* tcache_max -> tcache_bins
* tunables made SXID_IGNORE
* dedup fastbin removal code snippets
* document tunables
* document probes
* DeCamelCaseify

2 files changed, 53 insertions, 0 deletions

diff --git a/manual/probes.texi b/manual/probes.texi
index eb91c62703..96acaed206 100644
--- a/manual/probes.texi
+++ b/manual/probes.texi
@@ -231,6 +231,25 @@ dynamic brk/mmap thresholds.  Argument @var{$arg1} and @var{$arg2} are
 the adjusted mmap and trim thresholds, respectively.
 @end deftp
 
+@deftp Probe memory_tunable_tcache_max_bytes (int @var{$arg1}, int @var{$arg2})
+This probe is triggered when the @code{glibc.malloc.tcache_max}
+tunable is set.  Argument @var{$arg1} is the requested value, and
+@var{$arg2} is the previous value of this tunable.
+@end deftp
+
+@deftp Probe memory_tunable_tcache_count (int @var{$arg1}, int @var{$arg2})
+This probe is triggered when the @code{glibc.malloc.tcache_count}
+tunable is set.  Argument @var{$arg1} is the requested value, and
+@var{$arg2} is the previous value of this tunable.
+@end deftp
+
+@deftp Probe memory_tunable_tcache_unsorted_limit (int @var{$arg1}, int @var{$arg2})
+This probe is triggered when the
+@code{glibc.malloc.tcache_unsorted_limit} tunable is set.  Argument
+@var{$arg1} is the requested value, and @var{$arg2} is the previous
+value of this tunable.
+@end deftp
+
 @node Mathematical Function Probes
 @section Mathematical Function Probes
 
diff --git a/manual/tunables.texi b/manual/tunables.texi
index ac8c38fbde..b651a1d38d 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -190,3 +190,37 @@ number of arenas is determined by the number of CPU cores online.  For 32-bit
 systems the limit is twice the number of cores online and on 64-bit systems, it
 is 8 times the number of cores online.
 @end deftp
+
+@deftp Tunable glibc.malloc.tcache_max
+The maximum size of a request (in bytes) which may be met via the
+per-thread cache.  The default (and maximum) value is 1032 bytes on
+64-bit systems and 516 bytes on 32-bit systems.
+@end deftp
+
+@deftp Tunable glibc.malloc.tcache_count
+The maximum number of chunks of each size to cache.  The default is 7.
+There is no upper limit, other than available system memory.  Note
+that chunks are rounded up to malloc's guaranteed alignment - this
+count is per rounded size, not per user-provided size.
+
+The approximate maximum overhead of the per-thread cache (for each
+thread, of course) is thus @code{glibc.malloc.tcache_max} (in bins,
+max 64 bins) times @code{glibc.malloc.tcache_count} times the size for
+each bin.  With defaults, this is about 236 KB on 64-bit systems and
+118 KB on 32-bit systems.
+@end deftp
+
+@deftp Tunable glibc.malloc.tcache_unsorted_limit
+When the user requests memory and the request cannot be met via the
+per-thread cache, the arenas are used to meet the request.  At this
+time, additional chunks will be moved from existing arena lists to
+pre-fill the corresponding cache.  While copies from the fastbins,
+smallbins, and regular bins are bounded and predictable due to the bin
+sizes, copies from the unsorted bin are not bounded, and incur
+additional time penalties as they need to be sorted as they're
+scanned.  To make scanning the unsorted list more predictable and
+bounded, the user may set this tunable to limit the number of blocks
+that are scanned from the unsorted list while searching for chunks to
+pre-fill the per-thread cache with.  The default, or when set to zero,
+is no limit.
+@end deftp