[PATCH mm-unstable 4/5] mm: zsmalloc: Remove object mapping APIs and per-CPU map areas

[Yosry Ahmed]

zs_map_object() and zs_unmap_object() are no longer used, remove them.
Since these are the only users of per-CPU mapping_areas, remove them and
the associated CPU hotplug callbacks too.

Signed-off-by: Yosry Ahmed <yosry.ahmed@xxxxxxxxx>
---
 include/linux/cpuhotplug.h |   1 -
 include/linux/zsmalloc.h   |  21 ----
 mm/zsmalloc.c              | 226 +------------------------------------
 3 files changed, 1 insertion(+), 247 deletions(-)

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 6cc5e484547c1..1987400000b41 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -116,7 +116,6 @@ enum cpuhp_state {
 	CPUHP_NET_IUCV_PREPARE,
 	CPUHP_ARM_BL_PREPARE,
 	CPUHP_TRACE_RB_PREPARE,
-	CPUHP_MM_ZS_PREPARE,
 	CPUHP_MM_ZSWP_POOL_PREPARE,
 	CPUHP_KVM_PPC_BOOK3S_PREPARE,
 	CPUHP_ZCOMP_PREPARE,
diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h
index 7d70983cf3980..c26baf9fb331b 100644
--- a/include/linux/zsmalloc.h
+++ b/include/linux/zsmalloc.h
@@ -16,23 +16,6 @@
 
 #include <linux/types.h>
 
-/*
- * zsmalloc mapping modes
- *
- * NOTE: These only make a difference when a mapped object spans pages.
- */
-enum zs_mapmode {
-	ZS_MM_RW, /* normal read-write mapping */
-	ZS_MM_RO, /* read-only (no copy-out at unmap time) */
-	ZS_MM_WO /* write-only (no copy-in at map time) */
-	/*
-	 * NOTE: ZS_MM_WO should only be used for initializing new
-	 * (uninitialized) allocations.  Partial writes to already
-	 * initialized allocations should use ZS_MM_RW to preserve the
-	 * existing data.
-	 */
-};
-
 struct zs_pool_stats {
 	/* How many pages were migrated (freed) */
 	atomic_long_t pages_compacted;
@@ -48,10 +31,6 @@ void zs_free(struct zs_pool *pool, unsigned long obj);
 
 size_t zs_huge_class_size(struct zs_pool *pool);
 
-void *zs_map_object(struct zs_pool *pool, unsigned long handle,
-			enum zs_mapmode mm);
-void zs_unmap_object(struct zs_pool *pool, unsigned long handle);
-
 unsigned long zs_get_total_pages(struct zs_pool *pool);
 unsigned long zs_compact(struct zs_pool *pool);
 
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 56d6ed5c675b2..cd1c2a8ffef05 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -281,13 +281,6 @@ struct zspage {
 	struct zspage_lock zsl;
 };
 
-struct mapping_area {
-	local_lock_t lock;
-	char *vm_buf; /* copy buffer for objects that span pages */
-	char *vm_addr; /* address of kmap_local_page()'ed pages */
-	enum zs_mapmode vm_mm; /* mapping mode */
-};
-
 static void zspage_lock_init(struct zspage *zspage)
 {
 	static struct lock_class_key __key;
@@ -522,11 +515,6 @@ static struct zpool_driver zs_zpool_driver = {
 MODULE_ALIAS("zpool-zsmalloc");
 #endif /* CONFIG_ZPOOL */
 
-/* per-cpu VM mapping areas for zspage accesses that cross page boundaries */
-static DEFINE_PER_CPU(struct mapping_area, zs_map_area) = {
-	.lock	= INIT_LOCAL_LOCK(lock),
-};
-
 static inline bool __maybe_unused is_first_zpdesc(struct zpdesc *zpdesc)
 {
 	return PagePrivate(zpdesc_page(zpdesc));
@@ -1111,93 +1099,6 @@ static struct zspage *find_get_zspage(struct size_class *class)
 	return zspage;
 }
 
-static inline int __zs_cpu_up(struct mapping_area *area)
-{
-	/*
-	 * Make sure we don't leak memory if a cpu UP notification
-	 * and zs_init() race and both call zs_cpu_up() on the same cpu
-	 */
-	if (area->vm_buf)
-		return 0;
-	area->vm_buf = kmalloc(ZS_MAX_ALLOC_SIZE, GFP_KERNEL);
-	if (!area->vm_buf)
-		return -ENOMEM;
-	return 0;
-}
-
-static inline void __zs_cpu_down(struct mapping_area *area)
-{
-	kfree(area->vm_buf);
-	area->vm_buf = NULL;
-}
-
-static void *__zs_map_object(struct mapping_area *area,
-			struct zpdesc *zpdescs[2], int off, int size)
-{
-	size_t sizes[2];
-	char *buf = area->vm_buf;
-
-	/* disable page faults to match kmap_local_page() return conditions */
-	pagefault_disable();
-
-	/* no read fastpath */
-	if (area->vm_mm == ZS_MM_WO)
-		goto out;
-
-	sizes[0] = PAGE_SIZE - off;
-	sizes[1] = size - sizes[0];
-
-	/* copy object to per-cpu buffer */
-	memcpy_from_page(buf, zpdesc_page(zpdescs[0]), off, sizes[0]);
-	memcpy_from_page(buf + sizes[0], zpdesc_page(zpdescs[1]), 0, sizes[1]);
-out:
-	return area->vm_buf;
-}
-
-static void __zs_unmap_object(struct mapping_area *area,
-			struct zpdesc *zpdescs[2], int off, int size)
-{
-	size_t sizes[2];
-	char *buf;
-
-	/* no write fastpath */
-	if (area->vm_mm == ZS_MM_RO)
-		goto out;
-
-	buf = area->vm_buf;
-	buf = buf + ZS_HANDLE_SIZE;
-	size -= ZS_HANDLE_SIZE;
-	off += ZS_HANDLE_SIZE;
-
-	sizes[0] = PAGE_SIZE - off;
-	sizes[1] = size - sizes[0];
-
-	/* copy per-cpu buffer to object */
-	memcpy_to_page(zpdesc_page(zpdescs[0]), off, buf, sizes[0]);
-	memcpy_to_page(zpdesc_page(zpdescs[1]), 0, buf + sizes[0], sizes[1]);
-
-out:
-	/* enable page faults to match kunmap_local() return conditions */
-	pagefault_enable();
-}
-
-static int zs_cpu_prepare(unsigned int cpu)
-{
-	struct mapping_area *area;
-
-	area = &per_cpu(zs_map_area, cpu);
-	return __zs_cpu_up(area);
-}
-
-static int zs_cpu_dead(unsigned int cpu)
-{
-	struct mapping_area *area;
-
-	area = &per_cpu(zs_map_area, cpu);
-	__zs_cpu_down(area);
-	return 0;
-}
-
 static bool can_merge(struct size_class *prev, int pages_per_zspage,
 					int objs_per_zspage)
 {
@@ -1245,117 +1146,6 @@ unsigned long zs_get_total_pages(struct zs_pool *pool)
 }
 EXPORT_SYMBOL_GPL(zs_get_total_pages);
 
-/**
- * zs_map_object - get address of allocated object from handle.
- * @pool: pool from which the object was allocated
- * @handle: handle returned from zs_malloc
- * @mm: mapping mode to use
- *
- * Before using an object allocated from zs_malloc, it must be mapped using
- * this function. When done with the object, it must be unmapped using
- * zs_unmap_object.
- *
- * Only one object can be mapped per cpu at a time. There is no protection
- * against nested mappings.
- *
- * This function returns with preemption and page faults disabled.
- */
-void *zs_map_object(struct zs_pool *pool, unsigned long handle,
-			enum zs_mapmode mm)
-{
-	struct zspage *zspage;
-	struct zpdesc *zpdesc;
-	unsigned long obj, off;
-	unsigned int obj_idx;
-
-	struct size_class *class;
-	struct mapping_area *area;
-	struct zpdesc *zpdescs[2];
-	void *ret;
-
-	/*
-	 * Because we use per-cpu mapping areas shared among the
-	 * pools/users, we can't allow mapping in interrupt context
-	 * because it can corrupt another users mappings.
-	 */
-	BUG_ON(in_interrupt());
-
-	/* It guarantees it can get zspage from handle safely */
-	read_lock(&pool->lock);
-	obj = handle_to_obj(handle);
-	obj_to_location(obj, &zpdesc, &obj_idx);
-	zspage = get_zspage(zpdesc);
-
-	/*
-	 * migration cannot move any zpages in this zspage. Here, class->lock
-	 * is too heavy since callers would take some time until they calls
-	 * zs_unmap_object API so delegate the locking from class to zspage
-	 * which is smaller granularity.
-	 */
-	zspage_read_lock(zspage);
-	read_unlock(&pool->lock);
-
-	class = zspage_class(pool, zspage);
-	off = offset_in_page(class->size * obj_idx);
-
-	local_lock(&zs_map_area.lock);
-	area = this_cpu_ptr(&zs_map_area);
-	area->vm_mm = mm;
-	if (off + class->size <= PAGE_SIZE) {
-		/* this object is contained entirely within a page */
-		area->vm_addr = kmap_local_zpdesc(zpdesc);
-		ret = area->vm_addr + off;
-		goto out;
-	}
-
-	/* this object spans two pages */
-	zpdescs[0] = zpdesc;
-	zpdescs[1] = get_next_zpdesc(zpdesc);
-	BUG_ON(!zpdescs[1]);
-
-	ret = __zs_map_object(area, zpdescs, off, class->size);
-out:
-	if (likely(!ZsHugePage(zspage)))
-		ret += ZS_HANDLE_SIZE;
-
-	return ret;
-}
-EXPORT_SYMBOL_GPL(zs_map_object);
-
-void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
-{
-	struct zspage *zspage;
-	struct zpdesc *zpdesc;
-	unsigned long obj, off;
-	unsigned int obj_idx;
-
-	struct size_class *class;
-	struct mapping_area *area;
-
-	obj = handle_to_obj(handle);
-	obj_to_location(obj, &zpdesc, &obj_idx);
-	zspage = get_zspage(zpdesc);
-	class = zspage_class(pool, zspage);
-	off = offset_in_page(class->size * obj_idx);
-
-	area = this_cpu_ptr(&zs_map_area);
-	if (off + class->size <= PAGE_SIZE)
-		kunmap_local(area->vm_addr);
-	else {
-		struct zpdesc *zpdescs[2];
-
-		zpdescs[0] = zpdesc;
-		zpdescs[1] = get_next_zpdesc(zpdesc);
-		BUG_ON(!zpdescs[1]);
-
-		__zs_unmap_object(area, zpdescs, off, class->size);
-	}
-	local_unlock(&zs_map_area.lock);
-
-	zspage_read_unlock(zspage);
-}
-EXPORT_SYMBOL_GPL(zs_unmap_object);
-
 void *zs_obj_read_begin(struct zs_pool *pool, unsigned long handle,
 			void *local_copy)
 {
@@ -1975,7 +1765,7 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
 	 * the class lock protects zpage alloc/free in the zspage.
 	 */
 	spin_lock(&class->lock);
-	/* the zspage write_lock protects zpage access via zs_map_object */
+	/* the zspage write_lock protects zpage access via zs_obj_read/write() */
 	if (!zspage_write_trylock(zspage)) {
 		spin_unlock(&class->lock);
 		write_unlock(&pool->lock);
@@ -2459,23 +2249,11 @@ EXPORT_SYMBOL_GPL(zs_destroy_pool);
 
 static int __init zs_init(void)
 {
-	int ret;
-
-	ret = cpuhp_setup_state(CPUHP_MM_ZS_PREPARE, "mm/zsmalloc:prepare",
-				zs_cpu_prepare, zs_cpu_dead);
-	if (ret)
-		goto out;
-
 #ifdef CONFIG_ZPOOL
 	zpool_register_driver(&zs_zpool_driver);
 #endif
-
 	zs_stat_init();
-
 	return 0;
-
-out:
-	return ret;
 }
 
 static void __exit zs_exit(void)
@@ -2483,8 +2261,6 @@ static void __exit zs_exit(void)
 #ifdef CONFIG_ZPOOL
 	zpool_unregister_driver(&zs_zpool_driver);
 #endif
-	cpuhp_remove_state(CPUHP_MM_ZS_PREPARE);
-
 	zs_stat_exit();
 }
 
-- 
2.48.1.711.g2feabab25a-goog