Currently, we have two helpers that check for PMD-sized pages but have
different names and slightly different semantics:
- has_transparent_hugepage(): the name suggests it checks if THP is
enabled, but when CONFIG_TRANSPARENT_HUGEPAGE=y and the architecture
implements this helper, it actually checks if the CPU supports
PMD-sized pages
- thp_disabled_by_hw(): the name suggests it checks if THP is disabled
by the hardware, but it just returns a cached value acquired with
has_transparent_hugepage(). This helper is used in fast paths
This commit introduces a new helper called pgtable_has_pmd_leaves()
which is intended to replace both has_transparent_hugepage() and
thp_disabled_by_hw(). pgtable_has_pmd_leaves() has very clear semantics:
it returns true if the CPU supports PMD-sized pages and false otherwise.
It always returns a cached value, so it can be used in fast paths.
The new helper requires an initialization step which is performed by
init_arch_has_pmd_leaves(). We call init_arch_has_pmd_leaves() very
early during boot in start_kernel() so that users of the API can call it
from __setup() handlers.
The next commits will convert users of both has_transparent_hugepage()
and thp_disabled_by_hw() to pgtable_has_pmd_leaves().
Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
---
include/linux/pgtable.h | 7 +++++++
init/main.c | 1 +
mm/memory.c | 8 ++++++++
3 files changed, 16 insertions(+)
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 652f287c1ef6..6733f90a1da4 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -2017,6 +2017,13 @@ static inline const char *pgtable_level_to_str(enum pgtable_level level)
}
}
+extern bool __arch_has_pmd_leaves;
+static inline bool pgtable_has_pmd_leaves(void)
+{
+ return __arch_has_pmd_leaves;
+}
+void __init init_arch_has_pmd_leaves(void);
+
#endif /* !__ASSEMBLY__ */
#if !defined(MAX_POSSIBLE_PHYSMEM_BITS) && !defined(CONFIG_64BIT)
diff --git a/init/main.c b/init/main.c
index b84818ad9685..ad1209fffcde 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1036,6 +1036,7 @@ void start_kernel(void)
smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */
early_numa_node_init();
boot_cpu_hotplug_init();
+ init_arch_has_pmd_leaves();
print_kernel_cmdline(saved_command_line);
/* parameters may set static keys */
diff --git a/mm/memory.c b/mm/memory.c
index da360a6eb8a4..4c25a3c453c6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -177,6 +177,14 @@ static int __init init_zero_pfn(void)
}
early_initcall(init_zero_pfn);
+bool __arch_has_pmd_leaves __read_mostly;
+EXPORT_SYMBOL(__arch_has_pmd_leaves);
+
+void __init init_arch_has_pmd_leaves(void)
+{
+ __arch_has_pmd_leaves = has_transparent_hugepage();
+}
+
void mm_trace_rss_stat(struct mm_struct *mm, int member)
{
trace_rss_stat(mm, member);
--
2.53.0