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).
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.
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.
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.
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
In userspace ARM on Linux, zero-ing the high bits is the correct way to do this.
This doesn't fix the fact that we currently set LG_VADDR to 48 on ARM, when in
fact larger virtual address sizes are coming soon. We'll cross that bridge when
we come to it.
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.
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.
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.
To avoid complications, avoid invoking pthread_create "internally", instead rely
on thread0 to launch new threads, and also terminating threads when asked.
