mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2026-05-09 21:42:09 +02:00
Lance Yang
1fb3d8c20b
When freeing page tables, we try to batch them. If batch allocation fails (GFP_NOWAIT), __tlb_remove_table_one() immediately frees the one without batching. On !CONFIG_PT_RECLAIM, the fallback sends an IPI to all CPUs via tlb_remove_table_sync_one(). It disrupts all CPUs even when only a single process is unmapping memory. IPI broadcast was reported to hurt RT workloads[1]. tlb_remove_table_sync_one() synchronizes with lockless page-table walkers (e.g. GUP-fast) that rely on IRQ disabling. These walkers use local_irq_disable(), which is also an RCU read-side critical section. This patch introduces tlb_remove_table_sync_rcu() which uses RCU grace period (synchronize_rcu()) instead of IPI broadcast. This provides the same guarantee as IPI but without disrupting all CPUs. Since batch allocation already failed, we are in a slow path where sleeping is acceptable - we are in process context (unmap_region, exit_mmap) with only mmap_lock held. tlb_remove_table_sync_one() is retained for other callers (e.g., khugepaged after pmdp_collapse_flush(), tlb_finish_mmu() when tlb->fully_unshared_tables) that are not slow paths. Converting those may require different approaches such as targeted IPIs. Link: https://lore.kernel.org/linux-mm/1b27a3fa-359a-43d0-bdeb-c31341749367@kernel.org/ [1] Link: https://lore.kernel.org/linux-mm/20260202150957.GD1282955@noisy.programming.kicks-ass.net/ Link: https://lore.kernel.org/linux-mm/dfdfeac9-5cd5-46fc-a5c1-9ccf9bd3502a@intel.com/ Link: https://lore.kernel.org/linux-mm/bc489455-bb18-44dc-8518-ae75abda6bec@kernel.org/ Link: https://lkml.kernel.org/r/20260224142101.20500-1-lance.yang@linux.dev Signed-off-by: Lance Yang <lance.yang@linux.dev> Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org> Suggested-by: Dave Hansen <dave.hansen@intel.com> Suggested-by: David Hildenbrand (Arm) <david@kernel.org> Acked-by: David Hildenbrand (Arm) <david@kernel.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Nick Piggin <npiggin@gmail.com> Cc: Will Deacon <will@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>