[RFC PATCH v12 04/26] x86/tlb, riscv/tlb, mm/rmap: separate arch_tlbbatch_clear() out of arch_tlbbatch_flush()

Byungchul Park
2025-02-20T05:36:00Z

A new mechanism, LUF(Lazy Unmap Flush), defers tlb flush until folios
that have been unmapped and freed, eventually get allocated again. It's
safe for folios that had been mapped read only and were unmapped, since
the contents of the folios don't change while staying in pcp or buddy
so we can still read the data through the stale tlb entries.

This is a preparation for the mechanism that requires to avoid redundant
tlb flush by manipulating tlb batch's arch data. To achieve that, we
need to separate the part clearing the tlb batch's arch data out of
arch_tlbbatch_flush().

Signed-off-by: Byungchul Park <byungchul@sk.com>
---
arch/riscv/mm/tlbflush.c | 1 -
arch/x86/mm/tlb.c | 2 --
mm/rmap.c | 1 +
3 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index 9b6e86ce38674..36f996af6256c 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -201,5 +201,4 @@ void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
{
__flush_tlb_range(&batch->cpumask, FLUSH_TLB_NO_ASID, 0,
FLUSH_TLB_MAX_SIZE, PAGE_SIZE);
- cpumask_clear(&batch->cpumask);
}
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 86593d1b787d8..860e49b223fd7 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -1262,8 +1262,6 @@ void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
local_irq_enable();
}

- cpumask_clear(&batch->cpumask);
-
put_flush_tlb_info();
put_cpu();
}
diff --git a/mm/rmap.c b/mm/rmap.c
index c6c4d4ea29a7e..2de01de164ef0 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -648,6 +648,7 @@ void try_to_unmap_flush(void)
return;

arch_tlbbatch_flush(&tlb_ubc->arch);
+ arch_tlbbatch_clear(&tlb_ubc->arch);
tlb_ubc->flush_required = false;
tlb_ubc->writable = false;
}
--
2.17.1