mm: introduce common struct mm_slot

Patch series "add common struct mm_slot and use it in THP and KSM", v2.

At present, both THP and KSM module have similar structures mm_slot for
organizing and recording the information required for scanning mm, and
each defines the following exactly the same operation functions:

 - alloc_mm_slot
 - free_mm_slot
 - get_mm_slot
 - insert_to_mm_slots_hash

In order to de-duplicate these codes, this patchset introduces a common
struct mm_slot, and lets THP and KSM to use it.


This patch (of 7):

At present, both THP and KSM module have similar structures mm_slot for
organizing and recording the information required for scanning mm, and
each defines the following exactly the same operation functions:

 - alloc_mm_slot
 - free_mm_slot
 - get_mm_slot
 - insert_to_mm_slots_hash

In order to de-duplicate these codes, this patch introduces a common
struct mm_slot, and subsequent patches will let THP and KSM to use it.

Link: https://lkml.kernel.org/r/20220831031951.43152-1-zhengqi.arch@bytedance.com
Link: https://lkml.kernel.org/r/20220831031951.43152-2-zhengqi.arch@bytedance.comSigned-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mm_slot.h

+// SPDX-License-Identifier: GPL-2.0
+
+#ifndef _LINUX_MM_SLOT_H
+#define _LINUX_MM_SLOT_H
+
+#include <linux/hashtable.h>
+#include <linux/slab.h>
+
+/*
+ * struct mm_slot - hash lookup from mm to mm_slot
+ * @hash: link to the mm_slots hash list
+ * @mm_node: link into the mm_slots list
+ * @mm: the mm that this information is valid for
+ */
+struct mm_slot {
+	struct hlist_node hash;
+	struct list_head mm_node;
+	struct mm_struct *mm;
+};
+
+#define mm_slot_entry(ptr, type, member) \
+	container_of(ptr, type, member)
+
+static inline void *mm_slot_alloc(struct kmem_cache *cache)
+{
+	if (!cache)	/* initialization failed */
+		return NULL;
+	return kmem_cache_zalloc(cache, GFP_KERNEL);
+}
+
+static inline void mm_slot_free(struct kmem_cache *cache, void *objp)
+{
+	kmem_cache_free(cache, objp);
+}
+
+#define mm_slot_lookup(_hashtable, _mm) 				       \
+({									       \
+	struct mm_slot *tmp_slot, *mm_slot = NULL;			       \
+									       \
+	hash_for_each_possible(_hashtable, tmp_slot, hash, (unsigned long)_mm) \
+		if (_mm == tmp_slot->mm) {				       \
+			mm_slot = tmp_slot;				       \
+			break;						       \
+		}							       \
+									       \
+	mm_slot;							       \
+})
+
+#define mm_slot_insert(_hashtable, _mm, _mm_slot)			       \
+({									       \
+	_mm_slot->mm = _mm;						       \
+	hash_add(_hashtable, &_mm_slot->hash, (unsigned long)_mm);	       \
+})
+
+#endif /* _LINUX_MM_SLOT_H */