Option `experimental_hpa_max_purge_nhp` introduced for backward
compatibility reasons: to make it possible to have behaviour similar
to buggy `hpa_strict_min_purge_interval` implementation.
When `experimental_hpa_max_purge_nhp` is set to -1, there is no limit
to number of slabs we'll purge on each iteration. Otherwise, we'll purge
no more than `experimental_hpa_max_purge_nhp` hugepages (slabs). This in
turn means we might not purge enough dirty pages to satisfy
`hpa_dirty_mult` requirement.
Combination of `hpa_dirty_mult`, `experimental_hpa_max_purge_nhp` and
`hpa_strict_min_purge_interval` options allows us to have steady rate of
pages returned back to the system. This provides a strickier latency
guarantees as number of `madvise` calls is bounded (and hence number of
TLB shootdowns is limited) in exchange to weaker memory usage
guarantees.
There are few long options (`bin_shards` and `slab_sizes` for example)
when they are specified and we emit statistics value gets truncated.
Moved emitting logic for strings into separate `emitter_emit_str`
function. It will try to emit string same way as before and if value is
too long will fallback emiting rest partially with chunks of `BUF_SIZE`.
Justification for long strings (longer than `BUF_SIZE`) is not
supported.
Change in `hpa_min_purge_interval_ms` handling logic is not backward
compatible as it might increase memory usage. Now this logic guarded by
`hpa_strict_min_purge_interval` option.
When `hpa_strict_min_purge_interval` is true, we will purge no more than
`hpa_min_purge_interval_ms`. When `hpa_strict_min_purge_interval` is
false, old purging logic behaviour is preserved.
Long term strategy migrate all users of hpa to new logic and then delete
`hpa_strict_min_purge_interval` option.
This lets us easily see what fraction of flush load is being taken up by the
bins, and helps guide future optimization approaches (for example: should we
prefetch during cache bin fills? It depends on how many objects the average fill
pops out of the batch).
This adds a fast-path for threads freeing a small number of allocations to
bins which are not their "home-base" and which encounter lock contention in
attempting to do so. In producer-consumer workflows, such small lock hold times
can cause lock convoying that greatly increases overall bin mutex contention.
In the next commit, we'll start using the batcher to eliminate mutex traffic.
To avoid cluttering up that commit with the random bits of busy-work it entails,
we'll centralize them here. This commit introduces:
- A batched bin type.
- The ability to mix batched and unbatched bins in the arena.
- Conf parsing to set batches per size and a max batched size.
- mallctl access to the corresponding opt-namespace keys.
- Stats output of the above.
Bypassing background thread creation for the oversize_arena used to be an
optimization since that arena had eager purging. However #2466 changed the
purging policy for the oversize_arena -- specifically it switched to the default
decay time when background_thread is enabled.
This issue is noticable when the number of arenas is low: whenever the total #
of arenas is <= 4 (which is the default max # of background threads), in which
case the purging will be stalled since no background thread is created for the
oversize_arena.
This change adds support for writing pid namespaces to the filename of a
heap profile. When running with namespaces pids may reused across
namespaces and if mounts are shared where profiles are written there is
not a great way to differentiate profiles between pids.
Signed-off-by: Daniel Hodges <hodges.daniel.scott@gmail.com>
Signed-off-by: Daniel Hodges <hodgesd@fb.com>
Access nactive, ndirty and nmuzzy throught getters and not directly.
There are no functional change, but getters are required to propagate
HPA's statistics up to Page Allocator's statitics.
it's within the huge page size. These requests do not concern internal
fragmentation with huge pages, since the entire range is expected to be
accessed.
1. Pre-generate all default tcache ncached_max in tcache_boot;
2. Add getters returning default ncached_max and ncached_max_set;
3. Refactor tcache init so that it is always init with a given setting.
An allocation small enough will be promoted so that it does not
share an extent with others. However, when dalloc, such allocations
may not be dalloc as a promoted one if nbins < SC_NBINS. This
commit fixes the bug.
1. `thread_tcache_ncached_max_read_sizeclass` allows users to get the
ncached_max of the bin with the input sizeclass, passed in through
oldp (will be upper casted if not an exact bin size is given).
2. `thread_tcache_ncached_max_write` takes in a char array
representing the settings for bins in the tcache.
When using metadata_thp, allocate tcache bin stacks from base0, which means they
will be placed on huge pages along with other metadata, instead of mixed with
other regular allocations.
In order to do so, modified the base allocator to support limited reuse: freed
tcached stacks (from thread termination) will be returned to base0 and made
available for reuse, but no merging will be attempted since they were bump
allocated out of base blocks. These reused base extents are managed using
separately allocated base edata_t -- they are cached in base->edata_avail when
the extent is all allocated.
One tricky part is, stats updating must be skipped for such reused extents
(since they were accounted for already, and there is no purging for base). This
requires tracking the "if is reused" state explicitly and bypass the stats
updates when allocating from them.
1. add tcache_max and nhbins into tcache_t so that they are per-tcache,
with one auto tcache per thread, it's also per-thread;
2. add mallctl for each thread to set its own tcache_max (of its auto tcache);
3. store the maximum number of items in each bin instead of using a global storage;
4. add tests for the modifications above.
5. Rename `nhbins` and `tcache_maxclass` to `global_do_not_change_nhbins` and `global_do_not_change_tcache_maxclass`.
- `-Wmissing-prototypes` and `-Wmissing-variable-declarations` are
helpful for finding dead code and/or things that should be `static`
but aren't marked as such.
- `-Wunused-macros` is of similar utility, but for identifying dead macros.
- `-Wunreachable-code` and `-Wunreachable-code-aggressive` do exactly
what they say: flag unreachable code.
`read(2)` and `write(2)` may read or write fewer bytes than were
requested. In order to robustly ensure that all of the requested bytes
are read/written, these edge-cases must be handled.
There are several benefits to this:
1. It's cleaner and more reliable to use the builtin to
inform the compiler of assumptions instead of hoping that the
optimizer understands your intentions.
2. `clang` will warn you if any of your assumptions would produce
side-effects (which the compiler will discard). [This blog post](https://fastcompression.blogspot.com/2019/01/compiler-checked-contracts.html)
by Yann Collet highlights that a hazard of using the
`unreachable()`-based method of signaling assumptions is that it
can sometimes result in additional instructions being generated (see
[this Godbolt link](https://godbolt.org/z/lKNMs3) from the blog post
for an example).
As reported in #2449, under certain circumstances it's possible to get
stuck in an infinite loop attempting to purge from the HPA. We now
handle this by validating the HPA settings at the end of
configuration parsing and either normalizing them or aborting depending on
if `abort_conf` is set.
An arena's bins should normally be accessed via the `arena_get_bin`
function, which properly takes into account bin-shards. To ensure that
we don't accidentally commit code which incorrectly accesses the bins
directly, we mark the field with `__attribute__((deprecated))` with an
appropriate warning message, and suppress the warning in the few places
where directly accessing the bins is allowed.
In an attempt to make all headers self-contained, I inadvertently added
`#include`s which refer to intermediate, generated headers that aren't
included in the final install. Closes#2489.
