tree 13f433a0acda9287974efc538f63340e7ef0da3c
parent 656859d47895d077022be9bcec4435dba05c387f
author Willy Tarreau <w@1wt.eu> 1416946235 +0100
committer Willy Tarreau <w@1wt.eu> 1419461253 +0100
encoding latin1

MAJOR: session: implement a wait-queue for sessions who need a buffer

When a session_alloc_buffers() fails to allocate one or two buffers,
it subscribes the session to buffer_wq, and waits for another session
to release buffers. It's then removed from the queue and woken up with
TASK_WAKE_RES, and can attempt its allocation again.

We decide to try to wake as many waiters as we release buffers so
that if we release 2 and two waiters need only once, they both have
their chance. We must never come to the situation where we don't wake
enough tasks up.

It's common to release buffers after the completion of an I/O callback,
which can happen even if the I/O could not be performed due to half a
failure on memory allocation. In this situation, we don't want to move
out of the wait queue the session that was just added, otherwise it
will never get any buffer. Thus, we only force ourselves out of the
queue when freeing the session.

Note: at the moment, since session_alloc_buffers() is not used, no task
is subscribed to the wait queue.