This replaces the existing version on mm-unstable. The biggest difference is replacing local_lock entirely which is the last patch. The other changes are minor fixes reported by Hugh and Vlastimil. Changelog since v3 o Checkpatch fixes from mm-unstable (akpm) o Replace local_lock with spinlock (akpm) o Remove IRQ-disabled check in free_unref_page_list as it triggers a false positive (hughd) o Take an unlikely check out of the rmqueue fast path (vbabka) Some setups, notably NOHZ_FULL CPUs, may be running realtime or latency-sensitive applications that cannot tolerate interference due to per-cpu drain work queued by __drain_all_pages(). Introduce a new mechanism to remotely drain the per-cpu lists. It is made possible by remotely locking 'struct per_cpu_pages' new per-cpu spinlocks. This has two advantages, the time to drain is more predictable and other unrelated tasks are not interrupted. 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 cause a real-time task running on a NOHZ_FULL CPU to miss a deadline and at minimum, the draining is 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. This series adjusts the locking. A spinlock is added to struct per_cpu_pages to protect the list contents while local_lock_irq is ultimately replaced by just the spinlock in the final patch. This allows a remote CPU to safely. 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. 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. Patch 7 uses a normal spinlock instead of local_lock for remote draining include/linux/mm_types.h | 5 + include/linux/mmzone.h | 12 +- mm/page_alloc.c | 404 ++++++++++++++++++++++++--------------- 3 files changed, 266 insertions(+), 155 deletions(-) -- 2.35.3
