On Wed, Jan 05, 2022 at 07:46:48PM -0500, Daniel Jordan wrote: > padata threads hold mmap_lock as reader for the majority of their > runtime in order to call pin_user_pages_remote(), but they also > periodically take mmap_lock as writer for short periods to adjust > mm->locked_vm, hurting parallelism. > > Alleviate the write-side contention with a per-thread cache of locked_vm > which allows taking mmap_lock as writer far less frequently. > > Failure to refill the cache due to insufficient locked_vm will not cause > the entire pinning operation to error out. This avoids spurious failure > in case some pinned pages aren't accounted to locked_vm. > > Cache size is limited to provide some protection in the unlikely event > of a concurrent locked_vm accounting operation in the same address space > needlessly failing in case the cache takes more locked_vm than it needs. Why not just do the pinned page accounting once at the start? Why does it have to be done incrementally? Jason
