arena是jemalloc的总的管理块，一个进程中可以有多个arena，arena的最大个可以通过静态变量narenas_auto，。
可通过静态数组arenas获取进程中所有arena的指针：
(gdb) p narenas_auto
$359 = 2
(gdb) p *[email protected]
$360 = {0x7f93e02200, 0x7f93f12280}
可知，目前进程中arena的最大个数是2，它们的指针分别为0x7f93e02200，0x7f93f12280。
arena的声明如下:
typedef struct arena_s arena_t;
struct arena_s {
/* This arena‘s index within the arenas array. */
unsigned ind;
/*
* Number of threads currently assigned to this arena. This field is
* synchronized via atomic operations.
*/
unsigned nthreads;
/*
* There are three classes of arena operations from a locking
* perspective:
* 1) Thread assignment (modifies nthreads) is synchronized via atomics.
* 2) Bin-related operations are protected by bin locks.
* 3) Chunk- and run-related operations are protected by this mutex.
*/
malloc_mutex_t lock;
arena_stats_t stats;
/*
* List of tcaches for extant threads associated with this arena.
* Stats from these are merged incrementally, and at exit if
* opt_stats_print is enabled.
*/
ql_head(tcache_t) tcache_ql;
uint64_t prof_accumbytes;
/*
* PRNG state for cache index randomization of large allocation base
* pointers.
*/
uint64_t offset_state;
dss_prec_t dss_prec;
/*
* In order to avoid rapid chunk allocation/deallocation when an arena
* oscillates right on the cusp of needing a new chunk, cache the most
* recently freed chunk. The spare is left in the arena‘s chunk trees
* until it is deleted.
*
* There is one spare chunk per arena, rather than one spare total, in
* order to avoid interactions between multiple threads that could make
* a single spare inadequate.
*/
arena_chunk_t *spare;
/* Minimum ratio (log base 2) of nactive:ndirty. */
ssize_t lg_dirty_mult;
/* True if a thread is currently executing arena_purge_to_limit(). */
bool purging;
/* Number of pages in active runs and huge regions. */
size_t nactive;
/*
* Current count of pages within unused runs that are potentially
* dirty, and for which madvise(... MADV_DONTNEED) has not been called.
* By tracking this, we can institute a limit on how much dirty unused
* memory is mapped for each arena.
*/
size_t ndirty;
/*
* Unused dirty memory this arena manages. Dirty memory is conceptually
* tracked as an arbitrarily interleaved LRU of dirty runs and cached
* chunks, but the list linkage is actually semi-duplicated in order to
* avoid extra arena_chunk_map_misc_t space overhead.
*
* LRU-----------------------------------------------------------MRU
*
* /-- arena --- * | |
* | |
* |------------| /- chunk - * ...->|chunks_cache|<--------------------------->| /----\ |<--...
* |------------| | |node| |
* | | | | | |
* | | /- run -\ /- run -\ | | | |
* | | | | | | | | | |
* | | | | | | | | | |
* |------------| |-------| |-------| | |----| |
* ...->|runs_dirty |<-->|rd |<-->|rd |<---->|rd |<----...
* |------------| |-------| |-------| | |----| |
* | | | | | | | | | |
* | | | | | | | \----/ |
* | | \-------/ \-------/ | |
* | | | |
* | | | |
* \------------/ \---------/
*/
arena_runs_dirty_link_t runs_dirty;
extent_node_t chunks_cache;
/*
* Approximate time in seconds from the creation of a set of unused
* dirty pages until an equivalent set of unused dirty pages is purged
* and/or reused.
*/
ssize_t decay_time;
/* decay_time / SMOOTHSTEP_NSTEPS. */
nstime_t decay_interval;
/*
* Time at which the current decay interval logically started. We do
* not actually advance to a new epoch until sometime after it starts
* because of scheduling and computation delays, and it is even possible
* to completely skip epochs. In all cases, during epoch advancement we
* merge all relevant activity into the most recently recorded epoch.
*/
nstime_t decay_epoch;
/* decay_deadline randomness generator. */
uint64_t decay_jitter_state;
/*
* Deadline for current epoch. This is the sum of decay_interval and
* per epoch jitter which is a uniform random variable in
* [0..decay_interval). Epochs always advance by precise multiples of
* decay_interval, but we randomize the deadline to reduce the
* likelihood of arenas purging in lockstep.
*/
nstime_t decay_deadline;
/*
* Number of dirty pages at beginning of current epoch. During epoch
* advancement we use the delta between decay_ndirty and ndirty to
* determine how many dirty pages, if any, were generated, and record
* the result in decay_backlog.
*/
size_t decay_ndirty;
/*
* Memoized result of arena_decay_backlog_npages_limit() corresponding
* to the current contents of decay_backlog, i.e. the limit on how many
* pages are allowed to exist for the decay epochs.
*/
size_t decay_backlog_npages_limit;
/*
* Trailing log of how many unused dirty pages were generated during
* each of the past SMOOTHSTEP_NSTEPS decay epochs, where the last
* element is the most recent epoch. Corresponding epoch times are
* relative to decay_epoch.
*/
size_t decay_backlog[SMOOTHSTEP_NSTEPS];
/* Extant huge allocations. */
ql_head(extent_node_t) huge;
/* Synchronizes all huge allocation/update/deallocation. */
malloc_mutex_t huge_mtx;
/*
* Trees of chunks that were previously allocated (trees differ only in
* node ordering). These are used when allocating chunks, in an attempt
* to re-use address space. Depending on function, different tree
* orderings are needed, which is why there are two trees with the same
* contents.
*/
extent_tree_t chunks_szad_cached;
extent_tree_t chunks_ad_cached;
extent_tree_t chunks_szad_retained;
extent_tree_t chunks_ad_retained;
malloc_mutex_t chunks_mtx;
/* Cache of nodes that were allocated via base_alloc(). */
ql_head(extent_node_t) node_cache;
malloc_mutex_t node_cache_mtx;
/* User-configurable chunk hook functions. */
chunk_hooks_t chunk_hooks;
/* bins is used to store trees of free regions. */
arena_bin_t bins[NBINS];
/*
* Quantized address-ordered trees of this arena‘s available runs. The
* trees are used for first-best-fit run allocation.
*/
arena_run_tree_t runs_avail[1]; /* Dynamically sized. */
};
其他成员暂时不关注，这里我们先讨论bins这个arena_bin_t数组，数组大小是36，对应36种大小的region和run。
binind表示bins中的偏移，每一个binind对应一个固定大小的region。其对应关系为：
usize = index2size(binind);
size_tindex2size(szind_t index)
{
return (index2size_lookup(index));
}
size_t index2size_lookup(szind_t index)
{
size_t ret = (size_t)index2size_tab[index];
return (ret);
}
arena_bin_t的声明如下：
typedef struct arena_bin_s arena_bin_t;
struct arena_bin_s {
/*
* All operations on runcur, runs, and stats require that lock be
* locked. Run allocation/deallocation are protected by the arena lock,
* which may be acquired while holding one or more bin locks, but not
* vise versa.
*/
malloc_mutex_t lock;
/*
* Current run being used to service allocations of this bin‘s size
* class.
*/
arena_run_t *runcur;
/*
* Tree of non-full runs. This tree is used when looking for an
* existing run when runcur is no longer usable. We choose the
* non-full run that is lowest in memory; this policy tends to keep
* objects packed well, and it can also help reduce the number of
* almost-empty chunks.
*/
arena_run_tree_t runs;
/* Bin statistics. */
malloc_bin_stats_t stats;
};
runcur是当前可用于分配的run，
runs是个红黑树，链接当前arena中，所有可用的相同大小region对应的run，
如果runcur已满，就会从runs里找可用的run。
stats是当前bin对应的run和region的状态信息。
我们看一下实际运行过程中，bins中的index为5的一个arena_bin_t:
(gdb) p (*je_arenas[0])->bins[5]
$365 = {
lock = {
lock = {
__private = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
}
},
runcur = 0x7f68408ad0,
runs = {
rbt_root = 0x7f78e06e38
},
stats = {
nmalloc = 236529,
ndalloc = 229379,
nrequests = 1181919,
curregs = 7150,
nfills = 60225,
nflushes = 42510,
nruns = 64,
reruns = 5402,
curruns = 31
}
}
时间： 2024-10-27 06:20:56