mm: simplify and rename mm flags function for clarity

The __mm_flags_set_word() function is slightly ambiguous - we use 'set' to
refer to setting individual bits (such as in mm_flags_set()) but here we
use it to refer to overwriting the value altogether.

Rename it to __mm_flags_overwrite_word() to eliminate this ambiguity.

We additionally simplify the functions, eliminating unnecessary
bitmap_xxx() operations (the compiler would have optimised these out but
it's worth being as clear as we can be here).

Link: https://lkml.kernel.org/r/8f0bc55[e-mail]
Signed-off-by: Lorenzo Stoakes <[e-mail]>
Acked-by: Vlastimil Babka <[e-mail]>
Reviewed-by: Pedro Falcato <[e-mail]>
Acked-by: Alice Ryhl <[e-mail]> [rust]
Cc: Alex Gaynor <[e-mail]>
Cc: Alistair Popple <[e-mail]>
Cc: Andreas Hindborg <[e-mail]>
Cc: Axel Rasmussen <[e-mail]>
Cc: Baolin Wang <[e-mail]>
Cc: Baoquan He <[e-mail]>
Cc: Barry Song <[e-mail]>
Cc: Ben Segall <[e-mail]>
Cc: Björn Roy Baron <[e-mail]>
Cc: Boqun Feng <[e-mail]>
Cc: Byungchul Park <[e-mail]>
Cc: Chengming Zhou <[e-mail]>
Cc: Chris Li <[e-mail]>
Cc: Danilo Krummrich <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: David Rientjes <[e-mail]>
Cc: Dev Jain <[e-mail]>
Cc: Dietmar Eggemann <[e-mail]>
Cc: Gary Guo <[e-mail]>
Cc: Gregory Price <[e-mail]>
Cc: "Huang, Ying" <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jann Horn <[e-mail]>
Cc: Jason Gunthorpe <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: John Hubbard <[e-mail]>
Cc: Joshua Hahn <[e-mail]>
Cc: Juri Lelli <[e-mail]>
Cc: Kairui Song <[e-mail]>
Cc: Kees Cook <[e-mail]>
Cc: Kemeng Shi <[e-mail]>
Cc: Lance Yang <[e-mail]>
Cc: Leon Romanovsky <[e-mail]>
Cc: Liam Howlett <[e-mail]>
Cc: Mathew Brost <[e-mail]>
Cc: Matthew Wilcox (Oracle) <[e-mail]>
Cc: Mel Gorman <mgorman <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Miguel Ojeda <[e-mail]>
Cc: Mike Rapoport <[e-mail]>
Cc: Muchun Song <[e-mail]>
Cc: Nhat Pham <[e-mail]>
Cc: Nico Pache <[e-mail]>
Cc: Oscar Salvador <[e-mail]>
Cc: Peter Xu <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Qi Zheng <[e-mail]>
Cc: Rakie Kim <[e-mail]>
Cc: Rik van Riel <[e-mail]>
Cc: Ryan Roberts <[e-mail]>
Cc: Shakeel Butt <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Cc: Suren Baghdasaryan <[e-mail]>
Cc: Trevor Gross <[e-mail]>
Cc: Valentin Schneider <[e-mail]>
Cc: Vincent Guittot <[e-mail]>
Cc: Wei Xu <[e-mail]>
Cc: xu xin <[e-mail]>
Cc: Yuanchu Xie <[e-mail]>
Cc: Zi Yan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/mm_types.h

···
 	unsigned long cpu_bitmap[];
 };
 
-/* Set the first system word of mm flags, non-atomically. */
-static inline void __mm_flags_set_word(struct mm_struct *mm, unsigned long value)
+/* Copy value to the first system word of mm flags, non-atomically. */
+static inline void __mm_flags_overwrite_word(struct mm_struct *mm, unsigned long value)
 {
-	unsigned long *bitmap = ACCESS_PRIVATE(&mm->flags, __mm_flags);
-
-	bitmap_copy(bitmap, &value, BITS_PER_LONG);
+	*ACCESS_PRIVATE(&mm->flags, __mm_flags) = value;
 }
 
-/* Obtain a read-only view of the bitmap. */
+/* Obtain a read-only view of the mm flags bitmap. */
 static inline const unsigned long *__mm_flags_get_bitmap(const struct mm_struct *mm)
 {
 	return (const unsigned long *)ACCESS_PRIVATE(&mm->flags, __mm_flags);
···
 /* Read the first system word of mm flags, non-atomically. */
 static inline unsigned long __mm_flags_get_word(const struct mm_struct *mm)
 {
-	const unsigned long *bitmap = __mm_flags_get_bitmap(mm);
-
-	return bitmap_read(bitmap, 0, BITS_PER_LONG);
+	return *__mm_flags_get_bitmap(mm);
 }
 
 /*

kernel/fork.c

···
 	if (current->mm) {
 		unsigned long flags = __mm_flags_get_word(current->mm);
 
-		__mm_flags_set_word(mm, mmf_init_legacy_flags(flags));
+		__mm_flags_overwrite_word(mm, mmf_init_legacy_flags(flags));
 		mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
 	} else {
-		__mm_flags_set_word(mm, default_dump_filter);
+		__mm_flags_overwrite_word(mm, default_dump_filter);
 		mm->def_flags = 0;
 	}