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.
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..
I just added a new setting to set the number of reserved buffer, to
discover we already had one... Let's move the parsing of this keyword
(tune.buffers.reserve) and tune.buffers.limit to dynbuf.c where they
should be.
When recording the caller of a pool_alloc(), we currently store it only
when the object comes from the cache and never when it comes from the
heap. There's no valid reason for this except that the caller's pointer
was not passed to pool_alloc_nocache(), so it used to set NULL there.
Let's just pass it down the chain.
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.
The formatting of the buffer_dump() output must be calculated using the
relative counter, not the absolute one, or everything will be broken if
the <from> variable is not a multiple of 16.
Could be backported in all maintained versions.
They were strictly equivalent, let's remerge them and rename them to
pool_alloc_nocache() as it's the call which performs a real allocation
which does not check nor update the cache. The only difference in the
past was the former taking the lock and not the second but now the lock
is not needed anymore at this stage since the pool's list is not touched.
In addition, given that the "avail" argument is no longer used by the
function nor by its callers, let's drop it.
Since recent commit ae07592 ("MEDIUM: pools: add CONFIG_HAP_NO_GLOBAL_POOLS
and CONFIG_HAP_GLOBAL_POOLS") the pre-allocation of all desired reserved
buffers was not done anymore on systems not using the shared cache. This
basically has no practical impact since these ones will quickly be refilled
by all the ones used at run time, but it may confuse someone checking if
they're allocated in "show pools".
That's only 2.4-dev, no backport is needed.
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.
