The patch titled
Subject: lazy-tlb-shoot-lazies-a-non-refcounting-lazy-tlb-option-fix
has been added to the -mm tree. Its filename is
lazy-tlb-shoot-lazies-a-non-refcounting-lazy-tlb-option-fix.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/lazy-tlb-shoot-lazies-a-non-refcounting-lazy-tlb-option-fix.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/lazy-tlb-shoot-lazies-a-non-refcounting-lazy-tlb-option-fix.patch
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------------------------------------------------------
From: Nicholas Piggin <npiggin@xxxxxxxxx>
Subject: lazy-tlb-shoot-lazies-a-non-refcounting-lazy-tlb-option-fix
Update the comment to be clearer, and account for the improvement
to MMU_LAZY_TLB_REFCOUNT comment.
Link: https://lkml.kernel.org/r/1623121901.mszkmmum0n.astroid@xxxxxxxxx
Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Anton Blanchard <anton@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/Kconfig | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)
--- a/arch/Kconfig~lazy-tlb-shoot-lazies-a-non-refcounting-lazy-tlb-option-fix
+++ a/arch/Kconfig
@@ -423,15 +423,16 @@ config MMU_LAZY_TLB_REFCOUNT
def_bool y
depends on !MMU_LAZY_TLB_SHOOTDOWN
-# Instead of refcounting the lazy mm struct for kernel thread references
-# (which can cause contention with multi-threaded apps on large multiprocessor
-# systems), this option causes __mmdrop to IPI all CPUs in the mm_cpumask and
-# switch to init_mm if they were using the to-be-freed mm as the lazy tlb. To
-# implement this, architectures must use _lazy_tlb variants of mm refcounting
-# when releasing kernel thread mm references, and mm_cpumask must include at
-# least all possible CPUs in which the mm might be lazy, at the time of the
-# final mmdrop. mmgrab/mmdrop in arch/ code must be switched to _lazy_tlb
-# postfix as necessary.
+# This option allows MMU_LAZY_TLB_REFCOUNT=n. It ensures no CPUs are using an
+# mm as a lazy tlb beyond its last reference count, by shooting down these
+# users before the mm is deallocated. __mmdrop() first IPIs all CPUs that may
+# be using the mm as a lazy tlb, so that they may switch themselves to using
+# init_mm for their active mm. mm_cpumask(mm) is used to determine which CPUs
+# may be using mm as a lazy tlb mm.
+#
+# To implement this, an arch must ensure mm_cpumask(mm) contains at least all
+# possible CPUs in which the mm is lazy, and it must meet the requirements for
+# MMU_LAZY_TLB_REFCOUNT=n (see above).
config MMU_LAZY_TLB_SHOOTDOWN
bool
_
Patches currently in -mm which might be from npiggin@xxxxxxxxx are
lazy-tlb-introduce-lazy-mm-refcount-helper-functions.patch
lazy-tlb-introduce-lazy-mm-refcount-helper-functions-fix.patch
lazy-tlb-allow-lazy-tlb-mm-refcounting-to-be-configurable.patch
lazy-tlb-shoot-lazies-a-non-refcounting-lazy-tlb-option.patch
lazy-tlb-shoot-lazies-a-non-refcounting-lazy-tlb-option-fix.patch
powerpc-64s-enable-mmu_lazy_tlb_shootdown.patch
