Add new runtime option `debug_double_free_max_scan` that specifies the max
number of stack entries to scan in the cache bit when trying to detect the
double free bug (currently debug build only).
The option makes jemalloc use prctl with PR_SET_VMA to tag memory mappings with
"jemalloc_pg" or "jemalloc_pg_overcommit". This allows to easily identify
jemalloc's mappings in /proc/<pid>/maps. PR_SET_VMA is only available in Linux
5.17 and above.
At the time an attempt to compile jemalloc 5.3.0 with MSVC 2019 results in the followin error message:
> jemalloc/include/jemalloc/internal/edata.h:660: error C4576: a parenthesized type followed by an initializer list is a non-standard explicit type conversion syntax
Default SEC max_alloc option value was 32k, disabling SEC for platforms with
lg-page=16. This change enables SEC for all platforms, making minimum max_alloc
value equal to PAGE.
Before this commit, in case FreeBSD libc jemalloc was overridden by another
jemalloc, proper thread shutdown callback was involved only for the overriding
jemalloc. A call to _malloc_thread_cleanup from libthr would be redirected to
user jemalloc, leaving data about dead threads hanging in system jemalloc. This
change tackles the issue in two ways. First, for current and old system
jemallocs, which we can not modify, the overriding jemalloc would locate and
invoke system cleanup routine. For upcoming jemalloc integrations, the cleanup
registering function will also be redirected to user jemalloc, which means that
system jemalloc's cleanup routine will be registered in user's jemalloc and a
single call to _malloc_thread_cleanup will be sufficient to invoke both
callbacks.
While calculating the number of stashed pointers, multiple variables
potentially modified by a concurrent thread were used for the
calculation. This led to some inconsistencies, correctly detected by
the assertions. The change eliminates some possible inconsistencies by
using unmodified variables and only once a concurrently modified one.
The assertions are omitted for the cases where we acknowledge potential
inconsistencies too.
The option makes the process to exit with error code 1 if a memory leak
is detected. This is useful for implementing automated tools that rely
on leak detection.
On deallocation, sampled pointers (specially aligned) get junked and stashed
into tcache (to prevent immediate reuse). The expected behavior is to have
read-after-free corrupted and stopped by the junk-filling, while
write-after-free is checked when flushing the stashed pointers.
nstime module guarantees monotonic clock update within a single nstime_t. This
means, if two separate nstime_t variables are read and updated separately,
nstime_subtract between them may result in underflow. Fixed by switching to the
time since utility provided by nstime.
Currently used only for guarding purposes, the hint is used to determine
if the allocation is supposed to be frequently reused. For example, it
might urge the allocator to ensure the allocation is cached.
Some nstime_t operations require and assume the input nstime is initialized
(e.g. nstime_update) -- uninitialized input may cause silent failures which is
difficult to reproduce / debug. Add an explicit flag to track the state
(limited to debug build only).
Also fixed an use case in hpa (time of last_purge).
In order for nstime_update to handle non-monotonic clocks, it requires the input
nstime to be initialized -- when reading for the first time, zero init has to be
done. Otherwise random stack value may be seen as clocks and returned.
When opt_retain is on, slab extents remain guarded in all states, even
retained. This works well if arena is never destroyed, because we
anticipate those slabs will be eventually reused. But if the arena is
destroyed, the slabs must be unguarded to prevent leaking guard pages.
On the rtree metadata lookup fast path, there will never be a NULL returned when
the cache key matches (which is unknown to the compiler). The previous logic
was checking for NULL return value, resulting in the extra branch (in addition to
the cache key match checking). Make the lookup_fast return a bool to indicate
cache miss / match, so that the extra branch is avoided.
Adding guarded extents, which are regular extents surrounded by guard pages
(mprotected). To reduce syscalls, small guarded extents are cached as a
separate eset in ecache, and decay through the dirty / muzzy / retained pipeline
as usual.
This mallctl accepts an arena_config_t structure which
can be used to customize the behavior of the arena.
Right now it contains extent_hooks and a new option,
metadata_use_hooks, which controls whether the extent
hooks are also used for metadata allocation.
The medata_use_hooks option has two main use cases:
1. In heterogeneous memory systems, to avoid metadata
being placed on potentially slower memory.
2. Avoiding virtual memory from being leaked as a result
of metadata allocation failure originating in an extent hook.
Existing backtrace implementations skip native stack frames from runtimes like
Python. The hook allows to augment the backtraces to attribute allocations to
native functions in heap profiles.
This change allows every allocator conforming to PAI communicate that it
deferred some work for the future. Without it if a background thread goes into
indefinite sleep, there is no way to notify it about upcoming deferred work.
Previously the calculation of sleep time between wakeups was implemented within
background_thread. This resulted in some parts of decay and hpa specific
logic mixing with background thread implementation. In this change, background
thread delegates this calculation to arena and it, in turn, delegates it to PAI.
The next step is to implement the actual calculation of time until deferred work
in HPA.
Retained pages are those which haven't been touched and are unbacked from OS
perspective. For a pageslab their number should equal "total pages in slab"
minus "touched pages".
By force-inlining everything that would otherwise be a macro, we get the same
effect (it's not clear in the first place that this is actually a good idea, but
it avoids making any changes to the existing performance profile).
This makes the code more maintainable (in anticipation of subsequent changes),
as well as making performance profiles and debug info more readable (we get
"real" line numbers, instead of making everything point to the macro definition
of all associated functions).
The edata_cache_small had a fill/flush heuristic. In retrospect, this was a
premature optimization; more testing indicates that an unbounded cache is
effectively fine here, and moreover we spend a nontrivial amount of time doing
unnecessary filling/flushing.
As the HPA takes on a larger and larger fraction of all allocations, any
theoretical differences in allocation patterns should shrink. The HPA is more
efficient with its metadata in general, so it still comes out ahead on metadata
usage anyways.
We wait a while after deciding a huge extent should get hugified to see if it
gets purged before long. This avoids hugifying extents that might shortly get
dehugified for purging.
Rename and use the hpa_dehugification_threshold option support code for this,
since it's now ignored.
This is a simple multi-producer, single-consumer queue. The intended use case
is in the HPA, as we begin supporting hpdatas that move between hpa_shards. We
take just a single CAS as the cost to send a message (or a batch of messages) in
the low-contention case, and lock-freedom lets us avoid some lock-ordering
issues.
Now that all merging go through try_acquire_edata_neighbor, the mergeablility
checks (including head state checking) are done before reaching the merge hook.
In other words, merge hook will never be called if the head state doesn't agree.
Instead of passing down the new_addr, pass down the active edata which allows us
to always use a neighbor-acquiring semantic. In other words, this tells us both
the original edata and neighbor address. With this change, only neighbors of a
"known" edata can be acquired, i.e. acquiring an edata based on an arbitrary
address isn't possible anymore.
This avoids the addr-based mutexes (i.e. the mutex_pool), and instead relies on
the metadata tracked in rtree leaf: the head state and extent_state. Before
trying to access the neighbor edata (e.g. for coalescing), the states will be
verified first -- only neighbor edatas from the same arena and with the same
state will be accessed.
When retain is on, when extent_grow_retained failed (e.g. due to split hook
failures), we'll try extent_alloc_wrapper as the last resort. Set the is_head
bit in that case to be consistent. The allocated extent in that case will be
retained properly, but not merged with other extents.
Before this change, purge/hugify decisions had several sharp edges that could
lead to pathological behavior if tuning parameters weren't carefully chosen.
It's the first of a series; this introduces basic "make every hugepage with
dirty pages purgeable" functionality, and the next commit expands that
functionality to have a smarter policy for picking hugepages to purge.
Previously, the dehugify logic would *never* dehugify a hugepage unless it was
dirtier than the dehugification threshold. This can lead to situations in which
these pages (which themselves could never be purged) would push us above the
maximum allowed dirty pages in the shard. This forces immediate purging of any
pages deallocated in non-hugified hugepages, which in turn places nonobvious
practical limitations on the relationships between various config settings.
Instead, we make our preference not to dehugify to purge a soft one rather than
a hard one. We'll avoid purging them, but only so long as we can do so by
purging non-hugified pages. If we need to purge them to satisfy our dirty page
limits, or to hugify other, more worthy candidates, we'll still do so.
