diff options
| author | Lance Yang <lance.yang@linux.dev> | 2026-02-24 17:21:01 +0300 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2026-04-05 23:53:05 +0300 |
| commit | 1fb3d8c20bfadbbe2d9e5de18074de9282a52b5f (patch) | |
| tree | 76783b9e1ec9f394e090855b4b3fd935b1f76b94 /include | |
| parent | 77a9c445b668765129f877d3c0d08ec4dc3ce77b (diff) | |
| download | linux-1fb3d8c20bfadbbe2d9e5de18074de9282a52b5f.tar.xz | |
mm/mmu_gather: replace IPI with synchronize_rcu() when batch allocation fails
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>
Diffstat (limited to 'include')
| -rw-r--r-- | include/asm-generic/tlb.h | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h index 4aeac0c3d3f0..bdcc2778ac64 100644 --- a/include/asm-generic/tlb.h +++ b/include/asm-generic/tlb.h @@ -251,6 +251,8 @@ static inline void tlb_remove_table(struct mmu_gather *tlb, void *table) void tlb_remove_table_sync_one(void); +void tlb_remove_table_sync_rcu(void); + #else #ifdef tlb_needs_table_invalidate @@ -259,6 +261,8 @@ void tlb_remove_table_sync_one(void); static inline void tlb_remove_table_sync_one(void) { } +static inline void tlb_remove_table_sync_rcu(void) { } + #endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */ |