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Date: Tue, 16 Dec 2014 11:45:09 +0900
From: Minchan Kim <minchan@...nel.org>
To: Ganesh Mahendran <opensource.ganesh@...il.com>
Cc: ngupta@...are.org, akpm@...ux-foundation.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm/zsmalloc: add statistics support
On Sat, Dec 13, 2014 at 09:45:14PM +0800, Ganesh Mahendran wrote:
> As a ram based memory allocator, keep the fragmentation in a low level
Just say, zsmalloc.
> is our target. But now we still need to add the debug code in zsmalloc
> to get the quantitative data.
>
> After the RFC patch [1], Minchan Kim gave some suggestions.
> [1] https://patchwork.kernel.org/patch/5469301/
>
> This patch adds a new configuration CONFIG_ZSMALLOC_STAT to enable the statistics
> collection for developers. Currently only the objects information in each class
> are collected. User can get the information via debugfs. For example:
>
> After I copy file jdk-8u25-linux-x64.tar.gz to zram with ext4 filesystem.
> class size obj_allocated obj_used pages_used
> 0 32 0 0 0
> 1 48 256 12 3
> 2 64 64 14 1
> 3 80 51 7 1
> 4 96 128 5 3
> 5 112 73 5 2
> 6 128 32 4 1
> 7 144 0 0 0
> 8 160 0 0 0
> 9 176 0 0 0
> 10 192 0 0 0
> 11 208 0 0 0
> 12 224 0 0 0
> 13 240 0 0 0
> 14 256 16 1 1
> 15 272 15 9 1
> 16 288 0 0 0
> 17 304 0 0 0
> 18 320 0 0 0
> 19 336 0 0 0
> 20 352 0 0 0
> 21 368 0 0 0
> 22 384 0 0 0
> 23 400 0 0 0
> 24 416 0 0 0
> 25 432 0 0 0
> 26 448 0 0 0
> 27 464 0 0 0
> 28 480 0 0 0
> 29 496 33 1 4
> 30 512 0 0 0
> 31 528 0 0 0
> 32 544 0 0 0
> 33 560 0 0 0
> 34 576 0 0 0
> 35 592 0 0 0
> 36 608 0 0 0
> 37 624 0 0 0
> 38 640 0 0 0
> 40 672 0 0 0
> 42 704 0 0 0
> 43 720 17 1 3
> 44 736 0 0 0
> 46 768 0 0 0
> 49 816 0 0 0
> 51 848 0 0 0
> 52 864 14 1 3
> 54 896 0 0 0
> 57 944 13 1 3
> 58 960 0 0 0
> 62 1024 4 1 1
> 66 1088 15 2 4
> 67 1104 0 0 0
> 71 1168 0 0 0
> 74 1216 0 0 0
> 76 1248 0 0 0
> 83 1360 3 1 1
> 91 1488 11 1 4
> 94 1536 0 0 0
> 100 1632 5 1 2
> 107 1744 0 0 0
> 111 1808 9 1 4
> 126 2048 4 4 2
> 144 2336 7 3 4
> 151 2448 0 0 0
> 168 2720 15 15 10
> 190 3072 28 27 21
> 202 3264 0 0 0
> 254 4096 36209 36209 36209
>
> Total 37022 36326 36288
>
> We can see the overall fragentation is:
> (37022 - 36326) / 37022 = 1.87%
>
> Also from the statistics we know why we got so low fragmentation:
> Most of the objects is in class 254 with size 4096 Bytes. The pages in
> zspage is 1. And there is only one object in a page. So, No fragmentation
> will be produced.
>
> Also we can collect other information and show it to user in the future.
So, could you make zs
>
> Signed-off-by: Ganesh Mahendran <opensource.ganesh@...il.com>
> Suggested-by: Minchan Kim <minchan@...nel.org>
> ---
> mm/Kconfig | 10 ++++
> mm/zsmalloc.c | 164 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 174 insertions(+)
>
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 1d1ae6b..95c5728 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -601,6 +601,16 @@ config PGTABLE_MAPPING
> You can check speed with zsmalloc benchmark:
> https://github.com/spartacus06/zsmapbench
>
> +config ZSMALLOC_STAT
> + bool "Export zsmalloc statistics"
> + depends on ZSMALLOC
> + select DEBUG_FS
> + help
> + This option enables code in the zsmalloc to collect various
> + statistics about whats happening in zsmalloc and exports that
> + information to userspace via debugfs.
> + If unsure, say N.
> +
> config GENERIC_EARLY_IOREMAP
> bool
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index b724039..a8d0020 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -168,6 +168,8 @@ enum fullness_group {
> ZS_FULL
> };
>
> +static int zs_pool_num;
What's this? What protects the race?
It means description.
> +
> /*
> * number of size_classes
> */
> @@ -200,6 +202,11 @@ struct size_class {
> /* Number of PAGE_SIZE sized pages to combine to form a 'zspage' */
> int pages_per_zspage;
>
> +#ifdef CONFIG_ZSMALLOC_STAT
> + unsigned long obj_allocated;
> + unsigned long obj_used;
> +#endif
I perfer creating new struct.
struct zs_size_stat {
unsigend long obj_allocated;
unsignged long obj_used;
};
> +
> spinlock_t lock;
>
> struct page *fullness_list[_ZS_NR_FULLNESS_GROUPS];
> @@ -221,6 +228,10 @@ struct zs_pool {
>
> gfp_t flags; /* allocation flags used when growing pool */
> atomic_long_t pages_allocated;
> +
> +#ifdef CONFIG_ZSMALLOC_STAT
> + struct dentry *stat_dentry;
> +#endif
> };
>
> /*
> @@ -942,6 +953,132 @@ static bool can_merge(struct size_class *prev, int size, int pages_per_zspage)
> return true;
> }
>
> +
> +#ifdef CONFIG_ZSMALLOC_STAT
> +#include <linux/debugfs.h>
A question:
Why "#include" is here instead of top on the source file?
> +
> +static struct dentry *zs_stat_root;
> +
> +static int __init zs_stat_init(void)
> +{
> + if (!debugfs_initialized())
> + return -ENODEV;
Do we need above check?
When I read comment of debugfs_create_dir, it says
"If debugfs is not enabled in the kernel, the value -%ENODEV will be
returned."
> +
> + zs_stat_root = debugfs_create_dir("zsmalloc", NULL);
> + if (!zs_stat_root)
> + return -ENOMEM;
On null return of debugfs_create_dir, it means always ENOMEM?
> +
> + return 0;
> +}
> +
> +static void __exit zs_stat_exit(void)
> +{
> + debugfs_remove_recursive(zs_stat_root);
> +}
> +
> +static int zs_stats_show(struct seq_file *s, void *v)
> +{
> + int i;
> + struct zs_pool *pool = (struct zs_pool *)s->private;
> + struct size_class *class;
> + int objs_per_zspage;
> + unsigned long obj_allocated, obj_used, pages_used;
> + unsigned long total_objs = 0, total_used_objs = 0, total_pages = 0;
> +
> + seq_printf(s, " %5s %5s %13s %10s %10s\n", "class", "size",
> + "obj_allocated", "obj_used", "pages_used");
> +
> + for (i = 0; i < zs_size_classes; i++) {
> + class = pool->size_class[i];
> +
> + if (class->index != i)
> + continue;
> +
> + spin_lock(&class->lock);
> +
> + obj_allocated = class->obj_allocated;
> + obj_used = class->obj_used;
> + objs_per_zspage = get_maxobj_per_zspage(class->size,
> + class->pages_per_zspage);
> + pages_used = obj_allocated / objs_per_zspage *
> + class->pages_per_zspage;
I think We don't need to protect class->pages_per_zspage with class->lock.
> +
> + spin_unlock(&class->lock);
> +
> + seq_printf(s, " %5u %5u %10lu %10lu %10lu\n", i, class->size,
> + obj_allocated, obj_used, pages_used);
> +
> + total_objs += class->obj_allocated;
> + total_used_objs += class->obj_used;
You couldn't access class->fields without class lock.
Please, assign them into local variable under the lock and sum them without the lock.
> + total_pages += pages_used;
> + }
> +
> + seq_puts(s, "\n");
> + seq_printf(s, " %5s %5s %10lu %10lu %10lu\n", "Total", "",
> + total_objs, total_used_objs, total_pages);
> +
> + return 0;
> +}
> +
> +static int zs_stats_open(struct inode *inode, struct file *file)
> +{
> + return single_open(file, zs_stats_show, inode->i_private);
> +}
> +
> +static const struct file_operations zs_stats_operations = {
> + .open = zs_stats_open,
> + .read = seq_read,
> + .llseek = seq_lseek,
> + .release = single_release,
> +};
> +
> +static int zs_pool_stat_create(struct zs_pool *pool, int index)
> +{
> + char name[10];
> + int ret = 0;
> +
> + if (!zs_stat_root) {
> + ret = -ENODEV;
> + goto out;
> + }
> +
> + snprintf(name, sizeof(name), "pool-%d", index);
Hmm, how does admin know any zsmalloc instance is associated with
any block device?
Maybe we need export zspool index to the client and print it
when pool is populated.
> + pool->stat_dentry = debugfs_create_dir(name, zs_stat_root);
> + if (!pool->stat_dentry) {
> + ret = -ENOMEM;
> + goto out;
> + }
> +
> + debugfs_create_file("obj_in_classes", S_IFREG | S_IRUGO,
> + pool->stat_dentry, pool, &zs_stats_operations);
No need to check return?
> +
> +out:
> + return ret;
> +}
> +
> +static void zs_pool_stat_destroy(struct zs_pool *pool)
> +{
> + debugfs_remove_recursive(pool->stat_dentry);
> +}
> +
> +#else /* CONFIG_ZSMALLOC_STAT */
> +
> +static int __init zs_stat_init(void)
> +{
> + return 0;
> +}
> +
> +static void __exit zs_stat_exit(void) { }
> +
> +static inline int zs_pool_stat_create(struct zs_pool *pool, int index)
> +{
> + return 0;
> +}
> +
> +static inline void zs_pool_stat_destroy(struct zs_pool *pool) { }
> +
> +#endif
> +
> unsigned long zs_get_total_pages(struct zs_pool *pool)
> {
> return atomic_long_read(&pool->pages_allocated);
> @@ -1075,6 +1212,10 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
> atomic_long_add(class->pages_per_zspage,
> &pool->pages_allocated);
> spin_lock(&class->lock);
> +#ifdef CONFIG_ZSMALLOC_STAT
> + class->obj_allocated += get_maxobj_per_zspage(class->size,
> + class->pages_per_zspage);
> +#endif
I prefer zs_stat_inc(class, OBJ_ALLOCATED, get_max_obj());
> }
>
> obj = (unsigned long)first_page->freelist;
> @@ -1088,6 +1229,9 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
> kunmap_atomic(vaddr);
>
> first_page->inuse++;
> +#ifdef CONFIG_ZSMALLOC_STAT
> + class->obj_used++;
> +#endif
zs_stat_inc(class, OBJ_USED, 1)
> /* Now move the zspage to another fullness group, if required */
> fix_fullness_group(pool, first_page);
> spin_unlock(&class->lock);
> @@ -1127,12 +1271,19 @@ void zs_free(struct zs_pool *pool, unsigned long obj)
> first_page->freelist = (void *)obj;
>
> first_page->inuse--;
> +#ifdef CONFIG_ZSMALLOC_STAT
> + class->obj_used--;
> +#endif
zs_stat_dec(class, OBJ_USED, 1)
> fullness = fix_fullness_group(pool, first_page);
> spin_unlock(&class->lock);
>
> if (fullness == ZS_EMPTY) {
> atomic_long_sub(class->pages_per_zspage,
> &pool->pages_allocated);
> +#ifdef CONFIG_ZSMALLOC_STAT
> + class->obj_allocated -= get_maxobj_per_zspage(class->size,
> + class->pages_per_zspage);
> +#endif
zs_stat_dec(class, OBJ_ALLOCATED, get_max_obj());
> free_zspage(first_page);
> }
> }
> @@ -1209,6 +1360,10 @@ struct zs_pool *zs_create_pool(gfp_t flags)
> }
>
> pool->flags = flags;
> + zs_pool_num++;
Who protect the race?
And manybe we should keep the index in zspool and export it to the user
to let them know what zsmalloc instance is thiers.
> +
> + if (zs_pool_stat_create(pool, zs_pool_num))
> + pr_warn("zs pool %d stat initialization failed\n", zs_pool_num);
>
> return pool;
>
> @@ -1241,6 +1396,9 @@ void zs_destroy_pool(struct zs_pool *pool)
> kfree(class);
> }
>
> + zs_pool_stat_destroy(pool);
> + zs_pool_num--;
> +
> kfree(pool->size_class);
> kfree(pool);
> }
> @@ -1260,6 +1418,10 @@ static int __init zs_init(void)
> #ifdef CONFIG_ZPOOL
> zpool_register_driver(&zs_zpool_driver);
> #endif
> +
> + if (zs_stat_init())
> + pr_warn("zs stat initialization failed\n");
> +
> return 0;
> }
>
> @@ -1269,6 +1431,8 @@ static void __exit zs_exit(void)
> zpool_unregister_driver(&zs_zpool_driver);
> #endif
> zs_unregister_cpu_notifier();
> +
> + zs_stat_exit();
> }
>
> module_init(zs_init);
> --
> 1.7.9.5
>
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