In order to forcefully unregister a buffer waiter during an inter-thread
takeover under isolation, we'll need to that the function works without
th_ctx but the target thread's ctx instead. Let's implement this by
passing the target thread as an argument. Now b_dequeue() simply calls
this one with tid. It's OK it's not on that critical a path, especially
since the list has been checked for existence before performing the call.
Now, if a pool_alloc() fails for a buffer and if conditions are met
based on the queue number, we'll try to get an emergency buffer.
Thanks to this the situation is way more stable now. With only 4 reserve
buffers and 1 buffer it's possible to reliably serve 500 concurrent end-
to-end H1 connections and consult stats in parallel in loops showing the
growing number of buf_wait events in "show activity" without facing an
instant stall like in the past. Lower values still cause quick stalls
though.
It's also apparent that some subsystems do not seem to detach from the
buffer_wait lists when leaving. For example several crashes in the H1
part showed list elements still present after a free(), so maybe some
operations performed inside h1_release() after the b_dequeue() call
can sometimes result in a new allocation. Same for streams, where
the dequeue is done relatively early.
The buffer reserve set by tune.buffers.reserve has long been unused, and
in order to deal gracefully with failed memory allocations we'll need to
resort to a few emergency buffers that are pre-allocated per thread.
These buffers are only for emergency use, so every time their count is
below the configured number a b_free() will refill them. For this reason
their count can remain pretty low. We changed the default number from 2
to 4 per thread, and the minimum value is now zero (e.g. for low-memory
systems). The tune.buffers.limit setting has always been a problem when
trying to deal with the reserve but now we could simplify it by simply
pushing the limit (if set) to match the reserve. That was already done in
the past with a static value, but now with threads it was a bit trickier,
which is why the per-thread allocators increment the limit on the fly
before allocating their own buffers. This also means that the configured
limit is saner and now corresponds to the regular buffers that can be
allocated on top of emergency buffers.
At the moment these emergency buffers are not used upon allocation
failure. The only reason is to ease bisecting later if needed, since
this commit only has to deal with resource management.
Now b_alloc() will check the queues at the same and higher criticality
levels before allocating a buffer, and will refrain from allocating one
if these are not empty. The purpose is to put some priorities in the
allocation order so that most critical allocators are offered a chance
to complete.
However in order to permit a freshly dequeued task to allocate again while
siblings are still in the queue, there is a special DB_F_NOQUEUE flag to
pass to b_alloc() that will take care of this special situation.
Now that we need to keep the bitmap in sync with the list heads, we don't
want tasks to leave just doing a LIST_DEL_INIT() without updating the map.
Let's provide a b_dequeue() function for that purpose. The function detects
when it's going to remove the last element and figures the queue number
based on the pointer since it points to the root. It's not used yet.
Let's turn the buffer_wq into an array of 4 list heads. These are chosen
by criticality. The DB_CRIT_TO_QUEUE() macro maps each criticality level
into one of these 4 queues. The goal here clearly is to make it possible
to wake up the most critical queues in priority in order to let some tasks
finish their job and release buffers that others can use.
In order to avoid having to look up all queues, a bit map indicates which
queues are in use, which also allows to avoid looping in the most common
case where queues are empty..
When failing an allocation we always do the same dance, add the
buffer_wait struct to a list if it's not, and return. Let's just add
dedicated functions to centralize this, this will be useful to implement
a bit more complex logic.
For now they're not used.
The goal is to indicate how critical the allocation is, between the
least one (growing an existing buffer ring) and the topmost one (boot
time allocation for the life of the process).
The 3 tcp-based muxes (h1, h2, fcgi) use a common allocation function
to try to allocate otherwise subscribe. There's currently no distinction
of direction nor part that tries to allocate, and this should be revisited
to improve this situation, particularly when we consider that mux-h2 can
reduce its Tx allocations if needed.
For now, 4 main levels are planned, to translate how the data travels
inside haproxy from a producer to a consumer:
- MUX_RX: buffer used to receive data from the OS
- SE_RX: buffer used to place a transformation of the RX data for
a mux, or to produce a response for an applet
- CHANNEL: the channel buffer for sync recv
- MUX_TX: buffer used to transfer data from the channel to the outside,
generally a mux but there can be a few specificities (e.g.
http client's response buffer passed to the application,
which also gets a transformation of the channel data).
The other levels are a bit different in that they don't strictly need to
allocate for the first two ones, or they're permanent for the last one
(used by compression).
b_alloc() is used to allocate a buffer. We can provoke fault injection
based on forced memory allocation failures using -dMfail on the command
line, but we know that the buffer_wait list is a bit weak and doesn't
always recover well. As such, submitting buffer allocation to such a
treatment seriously limits the usefulness of -dMfail which cannot really
be used for other purposes. Let's just disable it for buffers for now.
When building with DEBUG_MEM_STATS, we only see b_alloc() and b_free() as
users of the "buffer" pool, because all call places rely on these more
convenient functions. It's annoying because it makes it very hard to see
which parts of the code are consuming buffers.
By switching the b_alloc() and b_free() inline functions to macros, we
can now finally track the users of struct buffer, e.g:
mux_h1.c:513 P_FREE size: 1275002880 calls: 38910 size/call: 32768 buffer
mux_h1.c:498 P_ALLOC size: 1912438784 calls: 58363 size/call: 32768 buffer
stream.c:763 P_FREE size: 4121493504 calls: 125778 size/call: 32768 buffer
stream.c:759 P_FREE size: 2061697024 calls: 62918 size/call: 32768 buffer
stream.c:742 P_ALLOC size: 3341123584 calls: 101963 size/call: 32768 buffer
stream.c:632 P_FREE size: 1275068416 calls: 38912 size/call: 32768 buffer
stream.c:631 P_FREE size: 637435904 calls: 19453 size/call: 32768 buffer
channel.h:850 P_ALLOC size: 4116480000 calls: 125625 size/call: 32768 buffer
channel.h:850 P_ALLOC size: 720896 calls: 22 size/call: 32768 buffer
dynbuf.c:55 P_FREE size: 65536 calls: 2 size/call: 32768 buffer
Let's do this since it doesn't change anything for the output code
(beyond adding the call places). Interestingly the code even got
slightly smaller now.
This macro just serves as an intermediary for __pool_alloc() and forwards
the flag. When DEBUG_MEM_STATS is set, it will be used to collect all
pool allocations including those which need to pass an explicit flag.
It's now used by b_alloc() which previously couldn't be tracked by
DEBUG_MEM_STATS, causing some free() calls to have no corresponding
allocations.
The last 3 fields were 3 list heads that are per-thread, and which are:
- the pool's LRU head
- the buffer_wq
- the streams list head
Moving them into thread_ctx completes the removal of dynamic elements
from the struct thread_info. Now all these dynamic elements are packed
together at a single place for a thread.
"f(void)" is the correct and preferred form for a function taking no
argument, while some places use the older "f()". These were reported
by clang's -Wmissing-prototypes, for example:
src/cpuset.c:111:5: warning: no previous prototype for function 'ha_cpuset_size' [-Wmissing-prototypes]
int ha_cpuset_size()
include/haproxy/cpuset.h:42:5: note: this declaration is not a prototype; add 'void' to make it a prototype for a zero-parameter function
int ha_cpuset_size();
^
void
This aggregate patch fixes this for the following functions:
ha_backtrace_to_stderr(), ha_cpuset_size(), ha_panic(), ha_random64(),
ha_thread_dump_all_to_trash(), get_exec_path(), check_config_validity(),
mworker_child_nb(), mworker_cli_proxy_(create|stop)(),
mworker_cleantasks(), mworker_cleanlisteners(), mworker_ext_launch_all(),
mworker_reload(), mworker_(env|proc_list)_to_(proc_list|env)(),
mworker_(un|)block_signals(), proxy_adjust_all_maxconn(),
proxy_destroy_all_defaults(), get_tainted(),
pool_total_(allocated|used)(), thread_isolate(_full|)(),
thread(_sync|)_release(), thread_harmless_till_end(),
thread_cpu_mask_forced(), dequeue_all_listeners(), next_timer_expiry(),
wake_expired_tasks(), process_runnable_tasks(), init_acl(),
init_buffer(), (de|)init_log_buffers(), (de|)init_pollers(),
fork_poller(), pool_destroy_all(), pool_evict_from_local_caches(),
pool_total_failures(), dump_pools_to_trash(), cfg_run_diagnostics(),
tv_init_(process|thread)_date(), __signal_process_queue(),
deinit_signals(), haproxy_unblock_signals()
The pool_alloc_dirty() function was renamed to __pool_alloc() and now
takes a set of flags indicating whether poisonning is permitted or not
and whether zeroing the area is needed or not. The pool_alloc() function
is now just a wrapper calling __pool_alloc(pool, 0).
It is never used anymore since 1.7 where it was used by b_alloc_margin()
then replaced by direct calls to the pools function, and it maintains a
dependency on the exposed pools functions. It's time to get rid of it,
as it's not even certain it still works.
Right now there is a discrepancy beteween b_alloc() and b_allow_margin():
the former forcefully overwrites the target pointer while the latter tests
it and returns it as-is if already allocated.
As a matter of fact, all callers of b_alloc() either preliminary test the
buffer, or assume it's already null.
Let's remove this pain and make the function test the buffer's allocation
before doing it again, and match call places' expectations.
Historically this function would try to wake the most accurate number of
process_stream() waiters. But since the introduction of filters which could
also require buffers (e.g. for compression), things started not to be as
accurate anymore. Nowadays muxes and transport layers also use buffers, so
the runqueue size has nothing to do anymore with the number of supposed
users to come.
In addition to this, the threshold was compared to the number of free buffer
calculated as allocated minus used, but this didn't work anymore with local
pools since these counts are not updated upon alloc/free!
Let's clean this up and pass the number of released buffers instead, and
consider that each waiter successfully called counts as one buffer. This
is not rocket science and will not suddenly fix everything, but at least
it cannot be as wrong as it is today.
This could have been marked as a bug given that the current situation is
totally broken regarding this, but this probably doesn't completely fix
it, it only goes in a better direction. It is possible however that it
makes sense in the future to backport this as part of a larger series if
the situation significantly improves.
The buffer wait queue used to be global historically but this doest not
make any sense anymore given that the most common use case is to have
thread-local pools. Thus there's no point waking up waiters of other
threads after releasing an entry, as they won't benefit from it.
Let's move the queue head to the thread_info structure and use
ti->buffer_wq from now on.
It looked strange to see pool_evict_from_cache() always very present
on "perf top", but there was actually a reason to this: while b_free()
uses pool_free() which properly disposes the buffer into the local cache
and b_alloc_fast() allocates using pool_get_first() which considers the
local cache, b_alloc_margin() does not consider the local cache as it
only uses __pool_get_first() which only allocates from the shared pools.
The impact is that basically everywhere a buffer is allocated (muxes,
streams, applets), it's always picked from the shared pool (hence
involves locking) and is released to the local one and makes it grow
until it's required to trigger a flush using pool_evict_from_cache().
Buffers usage are thus not thread-local at all, and cause eviction of
a lot of possibly useful objects from the local caches.
Just fixing this results in a 10% request rate increase in an HTTP/1 test
on a 16-thread machine.
This bug was caused by recent commit ed891fd ("MEDIUM: memory: make local
pools independent on lockless pools") merged into 2.2-dev9, so not backport
is needed.
There are list definitions everywhere in the code, let's drop the need
for including list-t.h to declare them. The rest of the list manipulation
is huge however and not needed everywhere so using the list walking macros
still requires to include list.h.
The pretty confusing "buffer.h" was in fact not the place to look for
the definition of "struct buffer" but the one responsible for dynamic
buffer allocation. As such it defines the struct buffer_wait and the
few functions to allocate a buffer or wait for one.
This patch moves it renaming it to dynbuf.h. The type definition was
moved to its own file since it's included in a number of other structs.
Doing this cleanup revealed that a significant number of files used to
rely on this one to inherit struct buffer through it but didn't need
anything from this file at all.
