Proposed fix for #1444 - ensure that `tls_callback` in the `#pragma comment(linker)`directive gets the same prefix added as it does i the C declaration.
This feature uses an dedicated arena to handle huge requests, which
significantly improves VM fragmentation. In production workload we tested it
often reduces VM size by >30%.
For low arena count settings, the huge threshold feature may trigger an unwanted
bg thd creation. Given that the huge arena does eager purging by default,
bypass bg thd creation when initializing the huge arena.
When custom extent_hooks or transparent huge pages are in use, the purging
semantics may change, which means we may not get zeroed pages on repopulating.
Fixing the issue by manually memset for such cases.
This makes it possible to have multiple set of bins in an arena, which improves
arena scalability because the bins (especially the small ones) are always the
limiting factor in production workload.
A bin shard is picked on allocation; each extent tracks the bin shard id for
deallocation. The shard size will be determined using runtime options.
If there are 3 or more threads spin-waiting on the same mutex,
there will be excessive exclusive cacheline contention because
pthread_trylock() immediately tries to CAS in a new value, instead
of first checking if the lock is locked.
This diff adds a 'locked' hint flag, and we will only spin wait
without trylock()ing while set. I don't know of any other portable
way to get the same behavior as pthread_mutex_lock().
This is pretty easy to test via ttest, e.g.
./ttest1 500 3 10000 1 100
Throughput is nearly 3x as fast.
This blames to the mutex profiling changes, however, we almost never
have 3 or more threads contending in properly configured production
workloads, but still worth fixing.
Refactor tcache_fill, introducing a new function arena_slab_reg_alloc_batch,
which will fill multiple pointers from a slab.
There should be no functional changes here, but allows future optimization
on reg_alloc_batch.
Add unsized and sized deallocation fastpaths. Similar to the malloc()
fastpath, this removes all frame manipulation for the majority of
free() calls. The performance advantages here are less than that
of the malloc() fastpath, but from prod tests seems to still be half
a percent or so of improvement.
Stats and sampling a both supported (sdallocx needs a sampling check,
for rtree lookups slab will only be set for unsampled objects).
We don't support flush, any flush requests go to the slowpath.
We eagerly coalesce large buffers when deallocating, however the previous logic
around this introduced extra lock overhead -- when coalescing we always lock the
neighbors even if they are active, while for active extents nothing can be done.
This commit checks if the neighbor extents are potentially active before
locking, and avoids locking if possible. This speeds up large_dalloc by ~20%.
It also fixes some undesired behavior: we could stop coalescing because a small
buffer was merged, while a large neighbor was ignored on the other side.
When retain is enabled, the default dalloc hook does nothing (since we avoid
munmap). But the overhead preparing the call is high, specifically the extent
de-register and re-register involve locking and extent / rtree modifications.
Bypass the call with retain in this diff.
This diff adds a fastpath that assumes size <= SC_LOOKUP_MAXCLASS, and
that we hit tcache. If either of these is false, we fall back to
the previous codepath (renamed 'malloc_default').
Crucially, we only tail call malloc_default, and with the same kind
and number of arguments, so that both clang and gcc tail-calling
will kick in - therefore malloc() gets treated as a leaf function,
and there are *no* caller-saved registers. Previously malloc() contained
5 caller saved registers on x64, resulting in at least 10 extra
memory-movement instructions.
In microbenchmarks this results in up to ~10% improvement in malloc()
fastpath. In real programs, this is a ~1% CPU and latency improvement
overall.
The experimental `smallocx` API is not exposed via header files,
requiring the users to peek at `jemalloc`'s source code to manually
add the external declarations to their own programs.
This should reinforce that `smallocx` is experimental, and that `jemalloc`
does not offer any kind of backwards compatiblity or ABI gurantees for it.
---
Motivation:
This new experimental memory-allocaction API returns a pointer to
the allocation as well as the usable size of the allocated memory
region.
The `s` in `smallocx` stands for `sized`-`mallocx`, attempting to
convey that this API returns the size of the allocated memory region.
It should allow C++ P0901r0 [0] and Rust Alloc::alloc_excess to make
use of it.
The main purpose of these APIs is to improve telemetry. It is more accurate
to register `smallocx(size, flags)` than `smallocx(nallocx(size), flags)`,
for example. The latter will always line up perfectly with the existing
size classes, causing a loss of telemetry information about the internal
fragmentation induced by potentially poor size-classes choices.
Instrumenting `nallocx` does not help much since user code can cache its
result and use it repeatedly.
---
Implementation:
The implementation adds a new `usize` option to `static_opts_s` and an `usize`
variable to `dynamic_opts_s`. These are then used to cache the result of
`sz_index2size` and similar functions in the code paths in which they are
unconditionally invoked. In the code-paths in which these functions are not
unconditionally invoked, `smallocx` calls, as opposed to `mallocx`, these
functions explicitly.
---
[0]: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0901r0.html
generation of sub bytes_until_sample, usize; je; for x86 arch.
Subtraction is unconditional, and only flags are checked for the jump,
no extra compare is necessary. This also reduces register pressure.
If we assume SC_LARGE_MAXCLASS will always fit in a SSIZE_T, then we can
optimize some checks by unconditional subtraction, and then checking flags
only, without a compare statement in x86.
in case `malloc_read_fd` returns a negative error number, the result
would afterwards be casted to an unsigned size_t, and may have
theoretically caused an out-of-bounds memory access in the following
`strncmp` call.
This makes it directly use MAP_EXCL and MAP_ALIGNED() instead
of weird workarounds involving mapping at random places and then
unmapping parts of them.
- Make API more clear for using as standalone json emitter
- Support cases that weren't possible before, e.g.
- emitting primitive values in an array
- emitting nested arrays
In case of multithreaded fork, we want to leave the child in a reasonable state,
in which tsd_nominal_tsds is either empty or contains only the forking thread.
The global data is mostly only used at initialization, or for easy access to
values we could compute statically. Instead of consuming that space (and
risking TLB misses), we can just pass around a pointer to stack data during
bootstrapping.
The largest small class, smallest large class, and largest large class may all
be needed down fast paths; to avoid the risk of touching another cache line, we
can make them available as constants.
I.e., parse before booting the bin module or sz module. This lets us tweak size
class settings before committing to them by letting them leak into other
modules.
This commit does not actually do any tweaking of the size classes; it *just*
chanchanges bootstrapping order; this may help bisecting any bootstrapping
failures on poorly-tested architectures.
This is the last big step in making size classes a runtime computation rather
than a configure-time one.
The compile-time computation has been left in, for now, to allow assertion
checking that the results are identical.
This class removes almost all the dependencies on size_classes.h, accessing the
data there only via the new module sc.h, which does not depend on any
configuration options.
In a subsequent commit, we'll remove the configure-time size class computations,
doing them at boot time, instead.
Before this commit jemalloc produced many warnings when compiled with -Wextra
with both Clang and GCC. This commit fixes the issues raised by these warnings
or suppresses them if they were spurious at least for the Clang and GCC
versions covered by CI.
This commit:
* adds `JEMALLOC_DIAGNOSTIC` macros: `JEMALLOC_DIAGNOSTIC_{PUSH,POP}` are
used to modify the stack of enabled diagnostics. The
`JEMALLOC_DIAGNOSTIC_IGNORE_...` macros are used to ignore a concrete
diagnostic.
* adds `JEMALLOC_FALLTHROUGH` macro to explicitly state that falling
through `case` labels in a `switch` statement is intended
* Removes all UNUSED annotations on function parameters. The warning
-Wunused-parameter is now disabled globally in
`jemalloc_internal_macros.h` for all translation units that include
that header. It is never re-enabled since that header cannot be
included by users.
* locally suppresses some -Wextra diagnostics:
* `-Wmissing-field-initializer` is buggy in older Clang and GCC versions,
where it does not understanding that, in C, `= {0}` is a common C idiom
to initialize a struct to zero
* `-Wtype-bounds` is suppressed in a particular situation where a generic
macro, used in multiple different places, compares an unsigned integer for
smaller than zero, which is always true.
* `-Walloc-larger-than-size=` diagnostics warn when an allocation function is
called with a size that is too large (out-of-range). These are suppressed in
the parts of the tests where `jemalloc` explicitly does this to test that the
allocation functions fail properly.
* adds a new CI build bot that runs the log unit test on CI.
Closes#1196 .
The feature allows using a dedicated arena for huge allocations. We want the
addtional arena to separate huge allocation because: 1) mixing small extents
with huge ones causes fragmentation over the long run (this feature reduces VM
size significantly); 2) with many arenas, huge extents rarely get reused across
threads; and 3) huge allocations happen way less frequently, therefore no
concerns for lock contention.
Previously, we made the user deal with this themselves, but that's not good
enough; if hooks may allocate, we should test the allocation pathways down
hooks. If we're doing that, we might as well actually implement the protection
for the user.
The hook module allows a low-reader-overhead way of finding hooks to invoke and
calling them.
For now, none of the allocation pathways are tied into the hooks; this will come
later.
"Hooks" is really the best name for the module that will contain the publicly
exposed hooks. So lets rename the current "hooks" module (that hook external
dependencies, for reentrancy testing) to "test_hooks".
When configured with --with-lg-page, it's possible for the configured page size
to be greater than the system page size, in which case the page address may only
be aligned with the system page size.
Previously, we would leak the extent and memory associated with a salvageable
portion of an extent that we were trying to split in three, in the case where
the first split attempt succeeded and the second failed.
Looking at the thread counts in our services, jemalloc's background thread
is useful, but mostly idle. Add a config option to tune down the number of threads.
preserve_lru feature adds lots of complication, for little value.
Removing it means merged extents are re-added to the lru list, and may
take longer to madvise away than they otherwise would.
Canaries after removal seem flat for several services (no change).
"always" marks all user mappings as MADV_HUGEPAGE; while "never" marks all
mappings as MADV_NOHUGEPAGE. The default setting "default" does not change any
settings. Note that all the madvise calls are part of the default extent hooks
by design, so that customized extent hooks have complete control over the
mappings including hugepage settings.
We have a buffer overrun that manifests in the case where arena indices higher
than the number of CPUs are accessed before arena indices lower than the number
of CPUs. This fixes the bug and adds a test.
On glibc and Android's bionic, strerror_r returns char* when
_GNU_SOURCE is defined.
Add a configure check for this rather than assume glibc is the
only libc that behaves this way.
We compute the max size required to satisfy an alignment. However this can be
quite pessimistic, especially with frequent reuse (and combined with state-based
fragmentation). This commit adds one more fit step specific to aligned
allocations, searching in all potential fit size classes.
The arena-associated stats are now all prefixed with arena_stats_, and live in
their own file. Likewise, malloc_bin_stats_t -> bin_stats_t, also in its own
file.
When purging, large allocations are usually the ones that cross the npages_limit
threshold, simply because they are "large". This means we often leave the large
extent around for a while, which has the downsides of: 1) high RSS and 2) more
chance of them getting fragmented. Given that they are not likely to be reused
very soon (LRU), let's over purge by 1 extent (which is often large and not
reused frequently).
Coalescing is a small price to pay for large allocations since they happen less
frequently. This reduces fragmentation while also potentially improving
locality.
When allocating from dirty extents (which we always prefer if available), large
active extents can get split even if the new allocation is much smaller, in
which case the introduced fragmentation causes high long term damage. This new
option controls the threshold to reuse and split an existing active extent. We
avoid using a large extent for much smaller sizes, in order to reduce
fragmentation. In some workload, adding the threshold improves virtual memory
usage by >10x.
While working on #852, I noticed the prng state is atomic. This is the only
atomic use of prng in all of jemalloc. Instead, use a threadlocal prng
state if possible to avoid unnecessary cache line contention.
Added an upper bound on how many pages we can decay during the current run.
Without this, decay could have unbounded increase in stashed, since other
threads could add new pages into the extents.
This option controls the max size when grow_retained. This is useful when we
have customized extent hooks reserving physical memory (e.g. 1G huge pages).
Without this feature, the default increasing sequence could result in fragmented
and wasted physical memory.
This attempts to use VM_OVERCOMMIT OID - newly introduced in -CURRENT
few days ago, specifically for this purpose - instead of querying the
sysctl by its string name. Due to how syctlbyname(3) works, this means
we do one syscall during binary startup instead of two.
Signed-off-by: Edward Tomasz Napierala <trasz@FreeBSD.org>
This avoids sysctl(2) syscall during binary startup, using the value
passed in the ELF aux vector instead.
Signed-off-by: Edward Tomasz Napierala <trasz@FreeBSD.org>
We observed that arena 0 can have much more metadata allocated comparing to
other arenas. Tune the auto mode to only switch to huge page on the 5th block
(instead of 3 previously) for a0.
Before this commit, extent_recycle_split intermingles the splitting of an extent
and the return of parts of that extent to a given extents_t. After it, that
logic is separated. This will enable splitting extents that don't live in any
extents_t (as the grow retained region soon will).
On x86 Linux, we define our own MADV_FREE if madvise(2) is available, but no
MADV_FREE is detected. This allows the feature to be built in and enabled with
runtime detection.
Since we allocate rtree nodes from a0's base, it's pushed to over 1 block on
initialization right away, which makes the auto thp mode less effective on a0.
We change a0 to make the switch on the 3rd block instead.
Quoting from https://github.com/jemalloc/jemalloc/issues/761 :
[...] reading the Power ISA documentation[1], the assembly in [the CPU_SPINWAIT
macro] isn't correct anyway (as @marxin points out): the setting of the
program-priority register is "sticky", and we never undo the lowering.
We could do something similar, but given that we don't have testing here in the
first place, I'm inclined to simply not try. I'll put something up reverting the
problematic commit tomorrow.
[1] Book II, chapter 3 of the 2.07B or 3.0B ISA documents.
There does not seem to be any overlap between usage of
extent_avail and extent_heap, so we can use the same hook.
The only remaining usage of rb trees is in the profiling code,
which has some 'interesting' iteration constraints.
Fixes#888
It's possible to build with lazy purge enabled but depoly to systems without
such support. In this case, rely on the boot time detection instead of keep
making unnecessary madvise calls (which all returns EINVAL).
If we guarantee no malloc activity in extent hooks, it's possible to make
customized hooks working on arena 0. Remove the non-a0 assertion to enable such
use cases.
To avoid the high RSS caused by THP + low usage arena (i.e. THP becomes a
significant percentage), added a new "auto" option which will only start using
THP after a base allocator used up the first THP region. Starting from the
second hugepage (in a single arena), "auto" behaves the same as "always",
i.e. madvise hugepage right away.
This eliminates the need for the arena stats code to "know" about tcaches; all
that it needs is a cache_bin_array_descriptor_t to tell it where to find
cache_bins whose stats it should aggregate.
This is the first step towards breaking up the tcache and arena (since they
interact primarily at the bin level). It should also make a future arena
caching implementation more straightforward.
As part of the metadata_thp support, We now have a separate swtich
(JEMALLOC_HAVE_MADVISE_HUGE) for MADV_HUGEPAGE availability. Use that instead
of JEMALLOC_THP (which doesn't guard pages_huge anymore) in tests.
The external linkage for spin_adaptive was not used, and the inline
declaration of spin_adaptive that was used caused a probem on FreeBSD
where CPU_SPINWAIT is implemented as a call to a static procedure for
x86 architectures.
If ptr is not page aligned, we know the allocation was not sampled. In this case
use the size passed into sdallocx directly w/o accessing rtree. This improve
sdallocx efficiency in the common case (not sampled && small allocation).
When retain is enabled, we should not attempt mmap for in-place expansion
(large_ralloc_no_move), because it's virtually impossible to succeed, and causes
unnecessary syscalls (which can cause lock contention under load).
Currently we have to log by writing something like:
static log_var_t log_a_b_c = LOG_VAR_INIT("a.b.c");
log (log_a_b_c, "msg");
This is sort of annoying. Let's just write:
log("a.b.c", "msg");
Currently, the log macro requires at least one argument after the format string,
because of the way the preprocessor handles varargs macros. We can hide some of
that irritation by pushing the extra arguments into a varargs function.
Older Linux systems don't have O_CLOEXEC. If that's the case, we fcntl
immediately after open, to minimize the length of the racy period in
which an
operation in another thread can leak a file descriptor to a child.
On OS X, we rely on the zone machinery to call our prefork and postfork
handlers.
In zone_force_unlock, we call jemalloc_postfork_child, reinitializing all our
mutexes regardless of state, since the mutex implementation will assert if the
tid of the unlocker is different from that of the locker. This has the effect
of unlocking the mutexes, but also fails to wake any threads waiting on them in
the parent.
To fix this, we track whether or not we're the parent or child after the fork,
and unlock or reinit as appropriate.
This resolves#895.
Passing is_background_thread down the decay path, so that background thread
itself won't attempt inactivity_check. This fixes an issue with background
thread doing trylock on a mutex it already owns.
We use the minimal_initilized tsd (which requires no cleanup) for free()
specifically, if tsd hasn't been initialized yet.
Any other activity will transit the state from minimal to normal. This is to
workaround the case where a thread has no malloc calls in its lifetime until
during thread termination, free() happens after tls destructors.
This issue caused the default extent alloc function to be incorrectly
used even when arena.<i>.extent_hooks is set. This bug was introduced
by 411697adcd (Use exponential series to
size extents.), which was first released in 5.0.0.
To avoid complications, avoid invoking pthread_create "internally", instead rely
on thread0 to launch new threads, and also terminating threads when asked.
Avoid holding arenas_lock and background_thread_lock when creating background
threads, because pthread_create may take internal locks, and potentially cause
deadlock with jemalloc internal locks.
Fix management of extent_grow_next to serialize operations that may grow
retained memory. This assures that the sizes of the newly allocated
extents correspond to the size classes in the intended growth sequence.
Fix management of extent_grow_next to skip size classes if a request is
too large to be satisfied by the next size in the growth sequence. This
avoids the potential for an arbitrary number of requests to bypass
triggering extent_grow_next increases.
This resolves#858.
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.
Drop the base mutex while allocating new base blocks, because extent
allocation can enter code that prohibits holding non-core mutexes, e.g.
the extent_[d]alloc() and extent_purge_forced_wrapper() calls in
extent_alloc_dss().
This partially resolves#802.
When # of dirty pages move below npages_limit (e.g. they are reused), we should
not lower number of unpurged pages because that would cause the reused pages to
be double counted in the backlog (as a result, decay happen slower than it
should). Instead, set number of unpurged to the greater of current npages and
npages_limit.
Added an assertion: the ceiling # of pages should be greater than npages_limit.
To avoid background threads sleeping forever with idle arenas, we eagerly check
background threads' sleep time after extents_dalloc, and signal the thread if
necessary.
Added opt.background_thread to enable background threads, which handles purging
currently. When enabled, decay ticks will not trigger purging (which will be
left to the background threads). We limit the max number of threads to NCPUs.
When percpu arena is enabled, set CPU affinity for the background threads as
well.
The sleep interval of background threads is dynamic and determined by computing
number of pages to purge in the future (based on backlog).
Instead of embedding a lock bit in rtree leaf elements, we associate extents
with a small set of mutexes. This gets us two things:
- We can use the system mutexes. This (hypothetically) protects us from
priority inversion, and lets us stop doing a backoff/sleep loop, instead
opting for precise wakeups from the mutex.
- Cuts down on the number of mutex acquisitions we have to do (from 4 in the
worst case to two).
We end up simplifying most of the rtree code (which no longer has to deal with
locking or concurrency at all), at the cost of additional complexity in the
extent code: since the mutex protecting the rtree leaf elements is determined by
reading the extent out of those elements, the initial read is racy, so that we
may acquire an out of date mutex. We re-check the extent in the leaf after
acquiring the mutex to protect us from this race.
This lets us specify whether and how mutexes of the same rank are allowed to be
acquired. Currently, we only allow two polices (only a single mutex at a given
rank at a time, and mutexes acquired in ascending order), but we can plausibly
allow more (e.g. the "release uncontended mutexes before blocking").
Support millisecond resolution for decay times. Among other use cases
this makes it possible to specify a short initial dirty-->muzzy decay
phase, followed by a longer muzzy-->clean decay phase.
This resolves#812.
Rather than using a manually maintained list of internal symbols to
drive name mangling, add a compilation phase to automatically extract
the list of internal symbols.
This resolves#677.
Instead, always define function pointers for interceptable functions,
but mark them const unless testing, so that the compiler can optimize
out the pointer dereferences.
This removes the tsd macros (which are used only for tsd_t in real builds). We
break up the circular dependencies involving tsd.
We also move all tsd access through getters and setters. This allows us to
assert that we only touch data when tsd is in a valid state.
We simplify the usages of the x macro trick, removing all the customizability
(get/set, init, cleanup), moving the lifetime logic to tsd_init and tsd_cleanup.
This lets us make initialization order independent of order within tsd_t.
Add the extent_destroy_t extent destruction hook to extent_hooks_t, and
use it during arena destruction. This hook explicitly communicates to
the callee that the extent must be destroyed or tracked for later reuse,
lest it be permanently leaked. Prior to this change, retained extents
could unintentionally be leaked if extent retention was enabled.
This resolves#560.
Control use of munmap(2) via a run-time option rather than a
compile-time option (with the same per platform default). The old
behavior of --disable-munmap can be achieved with
--with-malloc-conf=munmap:false.
This partially resolves#580.
This can catch bugs in which one header defines a numeric constant, and another
uses it without including the defining header. Undefined preprocessor symbols
expand to '0', so that this will compile fine, silently doing the math wrong.
Continue to use ivsalloc() when --enable-debug is specified (and add
assertions to guard against 0 size), but stop providing a documented
explicit semantics-changing band-aid to dodge undefined behavior in
sallocx() and malloc_usable_size(). ivsalloc() remains compiled in,
unlike when #211 restored --enable-ivsalloc, and if
JEMALLOC_FORCE_IVSALLOC is defined during compilation, sallocx() and
malloc_usable_size() will still use ivsalloc().
This partially resolves#580.
Some architectures like AArch64 may not have the open syscall because it
was superseded by the openat syscall, so check and use SYS_openat if
SYS_open is not available.
Additionally, Android headers for AArch64 define SYS_open to __NR_open,
even though __NR_open is undefined. Undefine SYS_open in that case so
SYS_openat is used.
Simplify configuration by removing the --disable-tcache option, but
replace the testing for that configuration with
--with-malloc-conf=tcache:false.
Fix the thread.arena and thread.tcache.flush mallctls to work correctly
if tcache is disabled.
This partially resolves#580.
Tracking extents is required by arena_reset. To support this, the extent
linkage was used for tracking 1) large allocations, and 2) full slabs. However
modifying the extent linkage could be an expensive operation as it likely incurs
cache misses. Since we forbid arena_reset on auto arenas, let's bypass the
linkage operations for auto arenas.
This avoids creating clean committed pages as a side effect of aligned
allocation. For configurations that decommit memory, purged pages are
decommitted, and decommitted extents cannot be coalesced with committed
extents. Unless the clean committed pages happen to be selected during
allocation, they cause unnecessary permanent extent fragmentation.
This resolves#766.
All mappings continue to be PAGE-aligned, even if the system page size
is smaller. This change is primarily intended to provide a mechanism
for supporting multiple page sizes with the same binary; smaller page
sizes work better in conjunction with jemalloc's design.
This resolves#467.
Some systems use a native 64 KiB page size, which means that the bitmap
for the smallest size class can be 8192 bits, not just 512 bits as when
the page size is 4 KiB. Linear search in bitmap_{sfu,ffu}() is
unacceptably slow for such large bitmaps.
This reverts commit 7c00f04ff4.
Rather than using a LIFO queue to track available extent_t structures,
use a red-black tree, and always choose the oldest/lowest available
during reuse.
Reverse the order of forced versus lazy purging attempts in
base_unmap(), in order to match the order in extent_dalloc_wrapper(),
which was reversed by 64e458f5cd
(Implement two-phase decay-based purging.).
Two levels of rcache is implemented: a direct mapped cache as L1, combined with
a LRU cache as L2. The L1 cache offers low cost on cache hit, but could suffer
collision under circumstances. This is complemented by the L2 LRU cache, which
is slower on cache access (overhead from linear search + reordering), but solves
collison of L1 rather well.
Previously we had a general detection and support of reentrancy, at the cost of
having branches and inc / dec operations on fast paths. To avoid taxing fast
paths, we move the reentrancy operations onto tsd slow state, and only modify
reentrancy level around external calls (that might trigger reentrancy).
Added tsd_state_nominal_slow, which on fast path malloc() incorporates
tcache_enabled check, and on fast path free() bundles both malloc_slow and
tcache_enabled branches.
With this change, when profiling is enabled, we avoid doing redundant rtree
lookups. Also changed dalloc_atx_t to alloc_atx_t, as it's now used on
allocation path as well (to speed up profiling).
This is a biggy. jemalloc_internal.h has been doing multiple jobs for a while
now:
- The source of system-wide definitions.
- The catch-all include file.
- The module header file for jemalloc.c
This commit splits up this functionality. The system-wide definitions
responsibility has moved to jemalloc_preamble.h. The catch-all include file is
now jemalloc_internal_includes.h. The module headers for jemalloc.c are now in
jemalloc_internal_[externs|inlines|types].h, just as they are for the other
modules.
This checks whether or not we're reentrant using thread-local data, and, if we
are, moves certain internal allocations to use arena 0 (which should be properly
initialized after bootstrapping).
The immediate thing this allows is spinning up threads in arena_new, which will
enable spinning up background threads there.
1) Re-organize TSD so that frequently accessed fields are closer to the
beginning and more compact. Assuming 64-bit, the first 2.5 cachelines now
contains everything needed on tcache fast path, expect the tcache struct itself.
2) Re-organize tcache and tbins. Take lg_fill_div out of tbin, and reduce tbin
to 24 bytes (down from 32). Split tbins into tbins_small and tbins_large, and
place tbins_small close to the beginning.
With the tcache change, we plan to leave some blank space when !config_debug
(unused tbins, witnesses) at the end of the tsd. Let's not touch the memory.
The embedded tcache is initialized upon tsd initialization. The avail arrays
for the tbins will be allocated / deallocated accordingly during init / cleanup.
With this change, the pointer to the auto tcache will always be available, as
long as we have access to the TSD. tcache_available() (called in tcache_get())
is provided to check if we should use tcache.
This will facilitate embedding tcache into tsd, which will require proper
initialization cannot be done via the static initializer. Make tsd->rtree_ctx
to be initialized via rtree_ctx_data_init().
Compact extent_t to 128 bytes on 64-bit systems by moving
arena_slab_data_t's nfree into extent_t's e_bits.
Cacheline-align extent_t structures so that they always cross the
minimum number of cacheline boundaries.
Re-order extent_t fields such that all fields except the slab bitmap
(and overlaid heap profiling context pointer) are in the first
cacheline.
This resolves#461.
Remove tree-structured bitmap support, in order to reduce complexity and
ease maintenance. No bitmaps larger than 512 bits have been necessary
since before 4.0.0, and there is no current plan that would increase
maximum bitmap size. Although tree-structured bitmaps were used on
32-bit platforms prior to this change, the overall benefits were
questionable (higher metadata overhead, higher bitmap modification cost,
marginally lower search cost).
For extents which do not delay coalescing, use first fit layout policy
rather than first-best fit layout policy. This packs extents toward
older virtual memory mappings, but at the cost of higher search overhead
in the common case.
This resolves#711.
A fixed max spin count is used -- with benchmark results showing it
solves almost all problems. As the benchmark used was rather intense,
the upper bound could be a little bit high. However it should offer a
good tradeoff between spinning and blocking.
Expand and restructure the rtree API such that all common operations can
be achieved with minimal work, regardless of whether the rtree leaf
fields are independent versus packed into a single atomic pointer.
This allows leaf elements to differ in size from internal node elements.
In principle it would be more correct to use a different type for each
level of the tree, but due to implementation details related to atomic
operations, we use casts anyway, thus counteracting the value of
additional type correctness. Furthermore, such a scheme would require
function code generation (via cpp macros), as well as either unwieldy
type names for leaves or type aliases, e.g.
typedef struct rtree_elm_d2_s rtree_leaf_elm_t;
This alternate strategy would be more correct, and with less code
duplication, but probably not worth the complexity.
Rather than storing usize only for large (and prof-promoted)
allocations, store the size class index for allocations that reside
within the extent, such that the size class index is valid for all
extents that contain extant allocations, and invalid otherwise (mainly
to make debugging simpler).
Split decay-based purging into two phases, the first of which uses lazy
purging to convert dirty pages to "muzzy", and the second of which uses
forced purging, decommit, or unmapping to convert pages to clean or
destroy them altogether. Not all operating systems support lazy
purging, yet the application may provide extent hooks that implement
lazy purging, so care must be taken to dynamically omit the first phase
when necessary.
The mallctl interfaces change as follows:
- opt.decay_time --> opt.{dirty,muzzy}_decay_time
- arena.<i>.decay_time --> arena.<i>.{dirty,muzzy}_decay_time
- arenas.decay_time --> arenas.{dirty,muzzy}_decay_time
- stats.arenas.<i>.pdirty --> stats.arenas.<i>.p{dirty,muzzy}
- stats.arenas.<i>.{npurge,nmadvise,purged} -->
stats.arenas.<i>.{dirty,muzzy}_{npurge,nmadvise,purged}
This resolves#521.
Refactor most of the decay-related functions to take as parameters the
decay_t and associated extents_t structures to operate on. This
prepares for supporting both lazy and forced purging on different decay
schedules.
These were all size_ts, so we have atomics support for them on all platforms, so
the conversion is straightforward.
Left non-atomic is curlextents, which AFAICT is not used atomically anywhere.
I expect this to be the trickiest conversion we will see, since we want atomics
on 64-bit platforms, but are also always able to piggyback on some sort of
external synchronization on non-64 bit platforms.
This has the dual advantages of allowing for sparsely used large
allocations, and relying on the kernel to supply zeroed pages, which
tends to be very fast on modern systems.
In the process, I changed the implementation of rtree_elm_acquire so that it
won't even try to CAS if its initial read (getting the extent + lock bit)
indicates that the CAS is doomed to fail. This can significantly improve
performance under contention.
The new feature, opt.percpu_arena, determines thread-arena association
dynamically based CPU id. Three modes are supported: "percpu", "phycpu"
and disabled.
"percpu" uses the current core id (with help from sched_getcpu())
directly as the arena index, while "phycpu" will assign threads on the
same physical CPU to the same arena. In other words, "percpu" means # of
arenas == # of CPUs, while "phycpu" has # of arenas == 1/2 * (# of
CPUs). Note that no runtime check on whether hyper threading is enabled
is added yet.
When enabled, threads will be migrated between arenas when a CPU change
is detected. In the current design, to reduce overhead from reading CPU
id, each arena tracks the thread accessed most recently. When a new
thread comes in, we will read CPU id and update arena if necessary.
When witness is enabled, lock rank order needs to be preserved during
prefork, not only for each arena, but also across arenas. This change
breaks arena_prefork into further stages to ensure valid rank order
across arenas. Also changed test/unit/fork to use a manual arena to
catch this case.
In the process, we can do some strength reduction, changing the fetch-adds and
fetch-subs to be simple loads followed by stores, since the modifications all
occur while holding the mutex.
This fixes tcache_flush for manual tcaches, which wasn't able to find
the correct arena it associated with. Also changed the decay test to
cover this case (by using manually created arenas).
This simplifies what would be pairing heap operations to the equivalent
of LIFO queue operations. This is a complementary optimization in the
context of delayed coalescing for cached extents.
Rather than purging uncoalesced extents, perform just enough incremental
coalescing to purge only fully coalesced extents. In the absence of
cached extent reuse, the immediate versus delayed incremental purging
algorithms result in the same purge order.
This resolves#655.
This is the first header refactoring diff, #533. It splits the assert and util
components into separate, hermetic, header files. In the process, it splits out
two of the large sub-components of util (the stdio.h replacement, and bit
manipulation routines) into their own components (malloc_io.h and bit_util.h).
This is mostly to break up cyclic dependencies, but it also breaks off a good
chunk of the catch-all-ness of util, which is nice.
Convert the nrequests field to be partially derived, and the curlextents
to be fully derived, in order to reduce the number of stats updates
needed during common operations.
This change affects ndalloc stats during arena reset, because it is no
longer possible to cancel out ndalloc effects (curlextents would become
negative).
This introduces a backport of C11 atomics. It has four implementations; ranked
in order of preference, they are:
- GCC/Clang __atomic builtins
- GCC/Clang __sync builtins
- MSVC _Interlocked builtins
- C11 atomics, from <stdatomic.h>
The primary advantages are:
- Close adherence to the standard API gives us a defined memory model.
- Type safety: atomic objects are now separate types from non-atomic ones, so
that it's impossible to mix up atomic and non-atomic updates (which is
undefined behavior that compilers are starting to take advantage of).
- Efficiency: we can specify ordering for operations, avoiding fences and
atomic operations on strongly ordered architectures (example:
`atomic_write_u32(ptr, val);` involves a CAS loop, whereas
`atomic_store(ptr, val, ATOMIC_RELEASE);` is a plain store.
This diff leaves in the current atomics API (implementing them in terms of the
backport). This lets us transition uses over piecemeal.
Testing:
This is by nature hard to test. I've manually tested the first three options on
Linux on gcc by futzing with the #defines manually, on freebsd with gcc and
clang, on MSVC, and on OS X with clang. All of these were x86 machines though,
and we don't have any test infrastructure set up for non-x86 platforms.
Remove obsolete unit test scaffolding for extent quantization. Remove
redundant assertions. Add an assertion to
extents_first_best_fit_locked() that should help prevent aligned
allocation regressions.
Extent splitting and coalescing is a major component of large allocation
overhead, and disabling coalescing of cached extents provides a simple
and effective hysteresis mechanism. Once two-phase purging is
implemented, it will probably make sense to leave coalescing disabled
for the first phase, but coalesce during the second phase.
This avoids a gcc diagnostic note:
note: The ABI for passing parameters with 64-byte alignment has
changed in GCC 4.6
This note related to the cacheline alignment of rtree_ctx_t, which was
introduced by 4a346f5593 (Replace rtree
path cache with LRU cache.).
Fix extent_alloc_dss() to account for bytes that are not a multiple of
the page size. This regression was introduced by
577d4572b0 (Make dss operations
lockless.), which was first released in 4.3.0.
