Hi Mel, On Thu, 2022-05-12 at 09:50 +0100, Mel Gorman wrote: > Changelog since v2 > o More conversions from page->lru to page->[pcp_list|buddy_list] > o Additional test results in changelogs > > Changelog since v1 > o Fix unsafe RT locking scheme > o Use spin_trylock on UP PREEMPT_RT > > This series has the same intent as Nicolas' series "mm/page_alloc: > Remote > per-cpu lists drain support" -- avoid interference of a high priority > task due to a workqueue item draining per-cpu page lists. While many > workloads can tolerate a brief interruption, it may be cause a real- > time > task runnning on a NOHZ_FULL CPU to miss a deadline and at minimum, > the draining in non-deterministic. > > Currently an IRQ-safe local_lock protects the page allocator per-cpu > lists. > The local_lock on its own prevents migration and the IRQ disabling > protects > from corruption due to an interrupt arriving while a page allocation > is > in progress. The locking is inherently unsafe for remote access > unless > the CPU is hot-removed. > > This series adjusts the locking. A spinlock is added to struct > per_cpu_pages to protect the list contents while local_lock_irq > continues > to prevent migration and IRQ reentry. This allows a remote CPU to > safely > drain a remote per-cpu list. > > This series is a partial series. Follow-on work should allow the > local_irq_save to be converted to a local_irq to avoid IRQs being > disabled/enabled in most cases. Consequently, there are some TODO > comments > highlighting the places that would change if local_irq was used. > However, > there are enough corner cases that it deserves a series on its own > separated by one kernel release and the priority right now is to > avoid > interference of high priority tasks. > > Patch 1 is a cosmetic patch to clarify when page->lru is storing > buddy pages > and when it is storing per-cpu pages. > > Patch 2 shrinks per_cpu_pages to make room for a spin lock. Strictly > speaking > this is not necessary but it avoids per_cpu_pages consuming > another > cache line. > > Patch 3 is a preparation patch to avoid code duplication. > > Patch 4 is a simple micro-optimisation that improves code flow > necessary for > a later patch to avoid code duplication. > > Patch 5 uses a spin_lock to protect the per_cpu_pages contents while > still > relying on local_lock to prevent migration, stabilise the pcp > lookup and prevent IRQ reentrancy. > > Patch 6 remote drains per-cpu pages directly instead of using a > workqueue. > > include/linux/mm_types.h | 5 + > include/linux/mmzone.h | 12 +- > mm/page_alloc.c | 348 +++++++++++++++++++++++++------------ > -- Thanks for the series! I'm testing the series ATM, both with on vanilla and RT kernels. I'll have the results by Monday. Regards, -- Nicolás Sáenz
