HPAGE_PMD_ORDER is used to determine a minimal amount of bits needed to store
per-node counters in struct collapse_control, defining the array to be either a
u16[HPAGE_PMD_ORDER] or u32[HPAGE_PMD_ORDER].
For some architectures/configs, HPAGE_PMD_ORDER isn't resolved at preprocessor
time (suitable for resolving preprocessor directives) but rather expands into a
compiler built-in that is resolved at compile-time. E.g. for 32-bit MIPS (see
link for full config):
---8<--
>> arch/mips/include/asm/pgtable.h:238:26: warning: "__builtin_ffs" is not defined, evaluates to 0 [-Wundef]
238 | #define PTE_T_LOG2 (__builtin_ffs(sizeof(pte_t)) - 1)
| ^~~~~~~~~~~~~
arch/mips/include/asm/pgtable-32.h:65:43: note: in expansion of macro 'PTE_T_LOG2'
65 | # define PGDIR_SHIFT (2 * PAGE_SHIFT - PTE_T_LOG2 - 1)
| ^~~~~~~~~~
include/asm-generic/pgtable-nop4d.h:11:33: note: in expansion of macro 'PGDIR_SHIFT'
11 | #define P4D_SHIFT PGDIR_SHIFT
| ^~~~~~~~~~~
include/asm-generic/pgtable-nopud.h:18:25: note: in expansion of macro 'P4D_SHIFT'
18 | #define PUD_SHIFT P4D_SHIFT
| ^~~~~~~~~
include/asm-generic/pgtable-nopmd.h:20:25: note: in expansion of macro 'PUD_SHIFT'
20 | #define PMD_SHIFT PUD_SHIFT
| ^~~~~~~~~
include/linux/huge_mm.h:109:25: note: in expansion of macro 'PMD_SHIFT'
109 | #define HPAGE_PMD_SHIFT PMD_SHIFT
| ^~~~~~~~~
include/linux/huge_mm.h:105:26: note: in expansion of macro 'HPAGE_PMD_SHIFT'
105 | #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
| ^~~~~~~~~~~~~~~
mm/khugepaged.c:90:5: note: in expansion of macro 'HPAGE_PMD_ORDER'
90 | #if HPAGE_PMD_ORDER < 16
| ^~~~~~~~~~~~~~~
>> arch/mips/include/asm/pgtable.h:238:39: error: missing binary operator before token "("
238 | #define PTE_T_LOG2 (__builtin_ffs(sizeof(pte_t)) - 1)
| ^
arch/mips/include/asm/pgtable-32.h:65:43: note: in expansion of macro 'PTE_T_LOG2'
65 | # define PGDIR_SHIFT (2 * PAGE_SHIFT - PTE_T_LOG2 - 1)
| ^~~~~~~~~~
include/asm-generic/pgtable-nop4d.h:11:33: note: in expansion of macro 'PGDIR_SHIFT'
11 | #define P4D_SHIFT PGDIR_SHIFT
| ^~~~~~~~~~~
include/asm-generic/pgtable-nopud.h:18:25: note: in expansion of macro 'P4D_SHIFT'
18 | #define PUD_SHIFT P4D_SHIFT
| ^~~~~~~~~
include/asm-generic/pgtable-nopmd.h:20:25: note: in expansion of macro 'PUD_SHIFT'
20 | #define PMD_SHIFT PUD_SHIFT
| ^~~~~~~~~
include/linux/huge_mm.h:109:25: note: in expansion of macro 'PMD_SHIFT'
109 | #define HPAGE_PMD_SHIFT PMD_SHIFT
| ^~~~~~~~~
include/linux/huge_mm.h:105:26: note: in expansion of macro 'HPAGE_PMD_SHIFT'
105 | #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
| ^~~~~~~~~~~~~~~
mm/khugepaged.c:90:5: note: in expansion of macro 'HPAGE_PMD_ORDER'
90 | #if HPAGE_PMD_ORDER < 16
| ^~~~~~~~~~~~~~~
---8<--
load_node is already special-cased for CONFIG_PPC64 in
"mm-khugepaged-add-struct-collapse_control-fix-fix", and we could continue down
that path by #define'ing away edge cases, but I think at this point it easier
to just let load_node be an array of u32s. If it's ever an issue, we can
revisit.
This essentially rolls back both:
"mm/khugepaged: use minimal bits to store num page < HPAGE_PMD_NR"
"mm-khugepaged-add-struct-collapse_control-fix-fix"
(though we'll leave it as a u32 vs an int).
Link: https://lore.kernel.org/linux-mm/202209021349.F73i5d6X-lkp@xxxxxxxxx/
Fixes: 5f7bb00bd9cd ("mm/khugepaged: use minimal bits to store num page < HPAGE_PMD_NR")
Fixes: 03053c821af2 ("mm-khugepaged-add-struct-collapse_control-fix-fix")
Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx>
---
mm/khugepaged.c | 7 +------
1 file changed, 1 insertion(+), 6 deletions(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index af3b07eb2389..29142a35d24c 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -93,13 +93,8 @@ struct collapse_control {
bool is_khugepaged;
/* Num pages scanned per node */
-#if defined(CONFIG_PPC64)
u32 node_load[MAX_NUMNODES];
-#elif HPAGE_PMD_ORDER < 16
- u16 node_load[MAX_NUMNODES];
-#else
- u32 node_load[MAX_NUMNODES];
-#endif
+
/* Last target selected in hpage_collapse_find_target_node() */
int last_target_node;
};
--
2.37.2.789.g6183377224-goog
