bcachefs: Don't use rep movsq for small memcopies

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bkey.h

@@ -95,8 +95,8 @@ do {								\
 		(u64 *) (_dst) < (u64 *) (_src) +		\
 		((struct bkey *) (_src))->u64s);		\
 								\
-	__memmove_u64s_down((_dst), (_src),			\
-			    ((struct bkey *) (_src))->u64s);	\
+	memcpy_u64s_small((_dst), (_src),			\
+			  ((struct bkey *) (_src))->u64s);	\
 } while (0)
 
 struct btree;

fs/bcachefs/extents.c

@@ -1457,8 +1457,8 @@ static inline void __extent_entry_insert(struct bkey_i *k,
 {
 	union bch_extent_entry *end = bkey_val_end(bkey_i_to_s(k));
 
-	memmove_u64s_up((u64 *) dst + extent_entry_u64s(new),
-			dst, (u64 *) end - (u64 *) dst);
+	memmove_u64s_up_small((u64 *) dst + extent_entry_u64s(new),
+			      dst, (u64 *) end - (u64 *) dst);
 	k->k.u64s += extent_entry_u64s(new);
 	memcpy_u64s_small(dst, new, extent_entry_u64s(new));
 }

fs/bcachefs/util.h

@@ -593,6 +593,24 @@ static inline void memmove_u64s_down(void *dst, const void *src,
 	__memmove_u64s_down(dst, src, u64s);
 }
 
+static inline void __memmove_u64s_up_small(void *_dst, const void *_src,
+					   unsigned u64s)
+{
+	u64 *dst = (u64 *) _dst + u64s;
+	u64 *src = (u64 *) _src + u64s;
+
+	while (u64s--)
+		*--dst = *--src;
+}
+
+static inline void memmove_u64s_up_small(void *dst, const void *src,
+					 unsigned u64s)
+{
+	EBUG_ON(dst < src);
+
+	__memmove_u64s_up_small(dst, src, u64s);
+}
+
 static inline void __memmove_u64s_up(void *_dst, const void *_src,
 				     unsigned u64s)
 {