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authorMinchan Kim <minchan@kernel.org>2015-04-15 16:15:23 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-04-15 16:35:20 -0700
commit2e40e163a25af3bd35d128d3e2e005916de5cce6 (patch)
tree9bda77ac0d126b198c18ddb9eedf5e2b32061449 /mm
parent018e9a49a554d915ba945a5faf34c592d65fe575 (diff)
zsmalloc: decouple handle and object
Recently, we started to use zram heavily and some of issues popped. 1) external fragmentation I got a report from Juneho Choi that fork failed although there are plenty of free pages in the system. His investigation revealed zram is one of the culprit to make heavy fragmentation so there was no more contiguous 16K page for pgd to fork in the ARM. 2) non-movable pages Other problem of zram now is that inherently, user want to use zram as swap in small memory system so they use zRAM with CMA to use memory efficiently. However, unfortunately, it doesn't work well because zRAM cannot use CMA's movable pages unless it doesn't support compaction. I got several reports about that OOM happened with zram although there are lots of swap space and free space in CMA area. 3) internal fragmentation zRAM has started support memory limitation feature to limit memory usage and I sent a patchset(https://lkml.org/lkml/2014/9/21/148) for VM to be harmonized with zram-swap to stop anonymous page reclaim if zram consumed memory up to the limit although there are free space on the swap. One problem for that direction is zram has no way to know any hole in memory space zsmalloc allocated by internal fragmentation so zram would regard swap is full although there are free space in zsmalloc. For solving the issue, zram want to trigger compaction of zsmalloc before it decides full or not. This patchset is first step to support above issues. For that, it adds indirect layer between handle and object location and supports manual compaction to solve 3th problem first of all. After this patchset got merged, next step is to make VM aware of zsmalloc compaction so that generic compaction will move zsmalloced-pages automatically in runtime. In my imaginary experiment(ie, high compress ratio data with heavy swap in/out on 8G zram-swap), data is as follows, Before = zram allocated object : 60212066 bytes zram total used: 140103680 bytes ratio: 42.98 percent MemFree: 840192 kB Compaction After = frag ratio after compaction zram allocated object : 60212066 bytes zram total used: 76185600 bytes ratio: 79.03 percent MemFree: 901932 kB Juneho reported below in his real platform with small aging. So, I think the benefit would be bigger in real aging system for a long time. - frag_ratio increased 3% (ie, higher is better) - memfree increased about 6MB - In buddy info, Normal 2^3: 4, 2^2: 1: 2^1 increased, Highmem: 2^1 21 increased frag ratio after swap fragment used : 156677 kbytes total: 166092 kbytes frag_ratio : 94 meminfo before compaction MemFree: 83724 kB Node 0, zone Normal 13642 1364 57 10 61 17 9 5 4 0 0 Node 0, zone HighMem 425 29 1 0 0 0 0 0 0 0 0 num_migrated : 23630 compaction done frag ratio after compaction used : 156673 kbytes total: 160564 kbytes frag_ratio : 97 meminfo after compaction MemFree: 89060 kB Node 0, zone Normal 14076 1544 67 14 61 17 9 5 4 0 0 Node 0, zone HighMem 863 50 1 0 0 0 0 0 0 0 0 This patchset adds more logics(about 480 lines) in zsmalloc but when I tested heavy swapin/out program, the regression for swapin/out speed is marginal because most of overheads were caused by compress/decompress and other MM reclaim stuff. This patch (of 7): Currently, handle of zsmalloc encodes object's location directly so it makes support of migration hard. This patch decouples handle and object via adding indirect layer. For that, it allocates handle dynamically and returns it to user. The handle is the address allocated by slab allocation so it's unique and we could keep object's location in the memory space allocated for handle. With it, we can change object's position without changing handle itself. Signed-off-by: Minchan Kim <minchan@kernel.org> Cc: Juneho Choi <juno.choi@lge.com> Cc: Gunho Lee <gunho.lee@lge.com> Cc: Luigi Semenzato <semenzato@google.com> Cc: Dan Streetman <ddstreet@ieee.org> Cc: Seth Jennings <sjennings@variantweb.net> Cc: Nitin Gupta <ngupta@vflare.org> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Mel Gorman <mel@csn.ul.ie> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/zsmalloc.c126
1 files changed, 98 insertions, 28 deletions
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 0dec1fa5f656..6f3cfbf5e237 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -110,6 +110,8 @@
#define ZS_MAX_ZSPAGE_ORDER 2
#define ZS_MAX_PAGES_PER_ZSPAGE (_AC(1, UL) << ZS_MAX_ZSPAGE_ORDER)
+#define ZS_HANDLE_SIZE (sizeof(unsigned long))
+
/*
* Object location (<PFN>, <obj_idx>) is encoded as
* as single (unsigned long) handle value.
@@ -140,7 +142,8 @@
/* ZS_MIN_ALLOC_SIZE must be multiple of ZS_ALIGN */
#define ZS_MIN_ALLOC_SIZE \
MAX(32, (ZS_MAX_PAGES_PER_ZSPAGE << PAGE_SHIFT >> OBJ_INDEX_BITS))
-#define ZS_MAX_ALLOC_SIZE PAGE_SIZE
+/* each chunk includes extra space to keep handle */
+#define ZS_MAX_ALLOC_SIZE (PAGE_SIZE + ZS_HANDLE_SIZE)
/*
* On systems with 4K page size, this gives 255 size classes! There is a
@@ -233,14 +236,24 @@ struct size_class {
* This must be power of 2 and less than or equal to ZS_ALIGN
*/
struct link_free {
- /* Handle of next free chunk (encodes <PFN, obj_idx>) */
- void *next;
+ union {
+ /*
+ * Position of next free chunk (encodes <PFN, obj_idx>)
+ * It's valid for non-allocated object
+ */
+ void *next;
+ /*
+ * Handle of allocated object.
+ */
+ unsigned long handle;
+ };
};
struct zs_pool {
char *name;
struct size_class **size_class;
+ struct kmem_cache *handle_cachep;
gfp_t flags; /* allocation flags used when growing pool */
atomic_long_t pages_allocated;
@@ -269,6 +282,34 @@ struct mapping_area {
enum zs_mapmode vm_mm; /* mapping mode */
};
+static int create_handle_cache(struct zs_pool *pool)
+{
+ pool->handle_cachep = kmem_cache_create("zs_handle", ZS_HANDLE_SIZE,
+ 0, 0, NULL);
+ return pool->handle_cachep ? 0 : 1;
+}
+
+static void destroy_handle_cache(struct zs_pool *pool)
+{
+ kmem_cache_destroy(pool->handle_cachep);
+}
+
+static unsigned long alloc_handle(struct zs_pool *pool)
+{
+ return (unsigned long)kmem_cache_alloc(pool->handle_cachep,
+ pool->flags & ~__GFP_HIGHMEM);
+}
+
+static void free_handle(struct zs_pool *pool, unsigned long handle)
+{
+ kmem_cache_free(pool->handle_cachep, (void *)handle);
+}
+
+static void record_obj(unsigned long handle, unsigned long obj)
+{
+ *(unsigned long *)handle = obj;
+}
+
/* zpool driver */
#ifdef CONFIG_ZPOOL
@@ -595,13 +636,18 @@ static void *obj_location_to_handle(struct page *page, unsigned long obj_idx)
* decoded obj_idx back to its original value since it was adjusted in
* obj_location_to_handle().
*/
-static void obj_handle_to_location(unsigned long handle, struct page **page,
+static void obj_to_location(unsigned long handle, struct page **page,
unsigned long *obj_idx)
{
*page = pfn_to_page(handle >> OBJ_INDEX_BITS);
*obj_idx = (handle & OBJ_INDEX_MASK) - 1;
}
+static unsigned long handle_to_obj(unsigned long handle)
+{
+ return *(unsigned long *)handle;
+}
+
static unsigned long obj_idx_to_offset(struct page *page,
unsigned long obj_idx, int class_size)
{
@@ -860,12 +906,16 @@ static void __zs_unmap_object(struct mapping_area *area,
{
int sizes[2];
void *addr;
- char *buf = area->vm_buf;
+ char *buf;
/* no write fastpath */
if (area->vm_mm == ZS_MM_RO)
goto out;
+ buf = area->vm_buf + ZS_HANDLE_SIZE;
+ size -= ZS_HANDLE_SIZE;
+ off += ZS_HANDLE_SIZE;
+
sizes[0] = PAGE_SIZE - off;
sizes[1] = size - sizes[0];
@@ -1153,13 +1203,14 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
enum zs_mapmode mm)
{
struct page *page;
- unsigned long obj_idx, off;
+ unsigned long obj, obj_idx, off;
unsigned int class_idx;
enum fullness_group fg;
struct size_class *class;
struct mapping_area *area;
struct page *pages[2];
+ void *ret;
BUG_ON(!handle);
@@ -1170,7 +1221,8 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
*/
BUG_ON(in_interrupt());
- obj_handle_to_location(handle, &page, &obj_idx);
+ obj = handle_to_obj(handle);
+ obj_to_location(obj, &page, &obj_idx);
get_zspage_mapping(get_first_page(page), &class_idx, &fg);
class = pool->size_class[class_idx];
off = obj_idx_to_offset(page, obj_idx, class->size);
@@ -1180,7 +1232,8 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
if (off + class->size <= PAGE_SIZE) {
/* this object is contained entirely within a page */
area->vm_addr = kmap_atomic(page);
- return area->vm_addr + off;
+ ret = area->vm_addr + off;
+ goto out;
}
/* this object spans two pages */
@@ -1188,14 +1241,16 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
pages[1] = get_next_page(page);
BUG_ON(!pages[1]);
- return __zs_map_object(area, pages, off, class->size);
+ ret = __zs_map_object(area, pages, off, class->size);
+out:
+ return ret + ZS_HANDLE_SIZE;
}
EXPORT_SYMBOL_GPL(zs_map_object);
void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
{
struct page *page;
- unsigned long obj_idx, off;
+ unsigned long obj, obj_idx, off;
unsigned int class_idx;
enum fullness_group fg;
@@ -1204,7 +1259,8 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
BUG_ON(!handle);
- obj_handle_to_location(handle, &page, &obj_idx);
+ obj = handle_to_obj(handle);
+ obj_to_location(obj, &page, &obj_idx);
get_zspage_mapping(get_first_page(page), &class_idx, &fg);
class = pool->size_class[class_idx];
off = obj_idx_to_offset(page, obj_idx, class->size);
@@ -1236,7 +1292,7 @@ EXPORT_SYMBOL_GPL(zs_unmap_object);
*/
unsigned long zs_malloc(struct zs_pool *pool, size_t size)
{
- unsigned long obj;
+ unsigned long handle, obj;
struct link_free *link;
struct size_class *class;
void *vaddr;
@@ -1244,9 +1300,15 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
struct page *first_page, *m_page;
unsigned long m_objidx, m_offset;
- if (unlikely(!size || size > ZS_MAX_ALLOC_SIZE))
+ if (unlikely(!size || (size + ZS_HANDLE_SIZE) > ZS_MAX_ALLOC_SIZE))
+ return 0;
+
+ handle = alloc_handle(pool);
+ if (!handle)
return 0;
+ /* extra space in chunk to keep the handle */
+ size += ZS_HANDLE_SIZE;
class = pool->size_class[get_size_class_index(size)];
spin_lock(&class->lock);
@@ -1255,8 +1317,10 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
if (!first_page) {
spin_unlock(&class->lock);
first_page = alloc_zspage(class, pool->flags);
- if (unlikely(!first_page))
+ if (unlikely(!first_page)) {
+ free_handle(pool, handle);
return 0;
+ }
set_zspage_mapping(first_page, class->index, ZS_EMPTY);
atomic_long_add(class->pages_per_zspage,
@@ -1268,40 +1332,45 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
}
obj = (unsigned long)first_page->freelist;
- obj_handle_to_location(obj, &m_page, &m_objidx);
+ obj_to_location(obj, &m_page, &m_objidx);
m_offset = obj_idx_to_offset(m_page, m_objidx, class->size);
vaddr = kmap_atomic(m_page);
link = (struct link_free *)vaddr + m_offset / sizeof(*link);
first_page->freelist = link->next;
- memset(link, POISON_INUSE, sizeof(*link));
+
+ /* record handle in the header of allocated chunk */
+ link->handle = handle;
kunmap_atomic(vaddr);
first_page->inuse++;
zs_stat_inc(class, OBJ_USED, 1);
/* Now move the zspage to another fullness group, if required */
fix_fullness_group(pool, first_page);
+ record_obj(handle, obj);
spin_unlock(&class->lock);
- return obj;
+ return handle;
}
EXPORT_SYMBOL_GPL(zs_malloc);
-void zs_free(struct zs_pool *pool, unsigned long obj)
+void zs_free(struct zs_pool *pool, unsigned long handle)
{
struct link_free *link;
struct page *first_page, *f_page;
- unsigned long f_objidx, f_offset;
+ unsigned long obj, f_objidx, f_offset;
void *vaddr;
int class_idx;
struct size_class *class;
enum fullness_group fullness;
- if (unlikely(!obj))
+ if (unlikely(!handle))
return;
- obj_handle_to_location(obj, &f_page, &f_objidx);
+ obj = handle_to_obj(handle);
+ free_handle(pool, handle);
+ obj_to_location(obj, &f_page, &f_objidx);
first_page = get_first_page(f_page);
get_zspage_mapping(first_page, &class_idx, &fullness);
@@ -1355,20 +1424,20 @@ struct zs_pool *zs_create_pool(char *name, gfp_t flags)
if (!pool)
return NULL;
- pool->name = kstrdup(name, GFP_KERNEL);
- if (!pool->name) {
- kfree(pool);
- return NULL;
- }
-
pool->size_class = kcalloc(zs_size_classes, sizeof(struct size_class *),
GFP_KERNEL);
if (!pool->size_class) {
- kfree(pool->name);
kfree(pool);
return NULL;
}
+ pool->name = kstrdup(name, GFP_KERNEL);
+ if (!pool->name)
+ goto err;
+
+ if (create_handle_cache(pool))
+ goto err;
+
/*
* Iterate reversly, because, size of size_class that we want to use
* for merging should be larger or equal to current size.
@@ -1450,6 +1519,7 @@ void zs_destroy_pool(struct zs_pool *pool)
kfree(class);
}
+ destroy_handle_cache(pool);
kfree(pool->size_class);
kfree(pool->name);
kfree(pool);

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