On 2022/8/30 03:51, Andrew Morton wrote:
On Mon, 29 Aug 2022 22:30:49 +0800 Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> wrote:
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.
Seems like a good idea.
--- /dev/null
+++ b/mm/mm_slot.h
@@ -0,0 +1,55 @@
+// 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;
+};
It appears that the presence of an mm_struct in the hash list does not
contribute to the mm_struct's refcount? That's somewhat unexpected.
Hi,
The reason is that khugepaged_exit()/ksm_exit() will be called first in
__mmput() to remove mm from the linked list. So it is prevented the
mm_struct from getting freed while on the list.
It would be helpful to add some words here describing the means by
which a user of mm_slot would prevent the mm_struct from getting freed
while on the list. I assume "caller must maintain a reference on the
mm_struct while it remains on an mm_slot hash list"?
+#define mm_slot_entry(ptr, type, member) \
+ container_of(ptr, type, member)
+
+static inline void *alloc_mm_slot(struct kmem_cache *cache)
+{
+ if (!cache) /* initialization failed */
+ return NULL;
+ return kmem_cache_zalloc(cache, GFP_KERNEL);
+}
+
+static inline void free_mm_slot(struct kmem_cache *cache, void *objp)
+{
+ kmem_cache_free(cache, objp);
+}
+
+#define get_mm_slot(_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; \
+})
Is there a reason why this must be implemented as a macro? That's
Since _hashtable is an array name, IIUC, this cannot be passed as a
function parameter, so I chose to implement it as a macro.
preferable, although this may be overly large for inlining. mm/util.c
might suit.
+#define insert_to_mm_slots_hash(_hashtable, _mm, _mm_slot) \
+({ \
+ _mm_slot->mm = _mm; \
+ hash_add(_hashtable, &_mm_slot->hash, (unsigned long)_mm); \
+})
Does this need to be a macro?
Ditto.
And the naming. Can we please have
mm_slot_entry
mm_slot_alloc
mm_slot_free
mm_slot_get
mm_slot_insert
Also, "get" usually implies that a refcout is taken on the obtained
object, so mm_slot_lookup() would be more appropriate.
These names are better, will modify to it in the next version.
Thanks,
Qi
--
Thanks,
Qi
