On Tue, Sep 05, 2017 at 04:30:18PM +0300, Alexander Shishkin wrote: > In order to work around the problem of using up mlocked memory for the > detached events, we can pin the ring buffer pages only while they are > in use (that is, the event is ACTIVE), and unpin them for the rest of > the time. When not pinned in, these pages can be swapped out. This way, > one user can have at most mlock_limit*nr_cpus kB of memory pinned at > any given moment, however many events they actually have. > > This enforces a constraint: pinning and unpinning may sleep and thus > can't be done in the event scheduling path. Instead, we use a task > work to do this, which this pattern us to userspace-only events. > Also, since one userspace thread only needs one buffer (for whatever > CPU it's running on at any given moment), we only do this for per-thread > events. > > The source for such swappable pages is shmemfs. This patch allows > allocating perf ring buffer pages from an shmemfs file if the above > constraints are met.
Right, so why still allow that previous icky thing? What cases do we need that for?
