This is the logo from the jemalloc development team's snazzy windbreakers. We
don't actually use it in any documentation yet, but there's no reason we
couldn't. In the meantime, it's probably best if it exists somewhere more
stable than various email inboxes.
For locality reasons, tcache bins are integrated in TSD. Allowing all size
classes to be cached has little benefit, but takes up much thread local storage.
In addition, it complicates the layout which we try hard to optimize.
Without a lock held continuously between checking tcaches_past and incrementing
it, it's possible for two threads to go down manual creation path
simultaneously. If the number of tcaches is one less than the maximum, it's
possible for both to create a tcache and increment tcaches_past, with the second
thread returning a value larger than TCACHES_MAX.
This comes in handy when overriding earlier settings to test alternate ones. We
don't really include tests for this, but I claim that's OK here:
- It's fairly straightforward
- It's fairly hard to test well
- This entire code path is undocumented and mostly for our internal
experimentation in the first place.
- I tested manually.
This will be the centralized component of the coming hugepage allocator; the
source of larger chunks of memory from which smaller ones can be obtained.
These had no uses and complicated the API. As a rule we now expect to only use
thread-local randomization for contention-reduction reasons, so we only pay the
API costs and never get the functionality benefits.
This introduces a new sort of edata_t; a pageslab, and a set to manage them.
This is part of a series of a commits to implement a hugepage allocator; the
pageset will be per-arena, and track small page allocations requests within a
larger extent allocated from a centralized hugepage allocator.
Specify the maximum number of regions in a slab, which is
(<lg-page> - <lg-tiny-min>) by default. This increases the limit of slab sizes
specified by "slab_sizes" in malloc_conf. This should never be less than
the default value. The max value of this option is related to LG_BITMAP_MAXBITS
(see more in bitmap.h).
For example, on a 4k page size system, if we:
1) configure jemalloc with with --with-lg-slab-maxregs=12.
2) export MALLOC_CONF="slab_sizes:9-16:4"
The slab size of 16 bytes is set to 4 pages. Previously, the default
lg-slab-maxregs is 9 (i.e. 12 - 3). The max slab size of 16 bytes is 2 pages
(i.e. (1<<9) * 16 bytes). By increasing the value from 9 to 12, the max slab
size can be set by MALLOC_CONF is 16 pages (i.e. (1<<12) * 16 bytes).
The mallctlbymib_long helper was copy-pasted from mallctlbymib_short, and
incorrectly used its output variable (a char *) rather than the output variable
of the mallctl call it was using (a uint64_t), causing breakages when
sizeof(char *) differed from sizeof(uint64_t).
This allows setting arenas per cpu dynamically, rather than forcing the user to
know the number of CPUs in advance if they want a particular CPU/space tradeoff.
The commit introducing size checks accidentally enabled them whenever any safety
checks were on. This ends up causing the regression that splitting up the
features was intended to avoid. Fix the issue.
The existing checks are good at finding such issues (on tcache flush), but not
so good at pinpointing them. Debug mode can find them, but sometimes debug mode
slows down a program so much that hard-to-hit bugs can take a long time to
crash.
This commit adds functionality to keep programs mostly on their fast paths,
while also checking every sized delete argument they get.
