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Date: Wed, 17 Dec 2014 15:05:19 +0800
From: Ganesh Mahendran <opensource.ganesh@...il.com>
To: Minchan Kim <minchan@...nel.org>
Cc: Nitin Gupta <ngupta@...are.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux-MM <linux-mm@...ck.org>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm/zsmalloc: add statistics support
Hello, Minchan
Thanks for your review.
2014-12-16 10:45 GMT+08:00 Minchan Kim <minchan@...nel.org>:
> 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.
Ok.
>
>> 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
Ok
>>
>> 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 is the pool index. Yes, there is problem here.
I will change it to atomic and increased every time a new zs pool created.
And then name the /sys/kernel/debug/pool-x using this index.
static atomic_t zs_pool_index = ATOMIC_INIT(0);
...
pool->index = atomic_inc_return(&zs_pool_index);
> 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;
> };
Got it, I will redo this.
>
>> +
>> 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?
Yes, the "#include ..." should be on the top of the source file.
I will modify it.
>
>> +
>> +static struct dentry *zs_stat_root;
>> +
>> +static int __init zs_stat_init(void)
>> +{
>> + if (!debugfs_initialized())
>> + return -ENODEV;
>
> Do we need above check?
Yes, I think we need this check.
When debugfs module init failed, we should not go ahead here.
>
> When I read comment of debugfs_create_dir, it says
> "If debugfs is not enabled in the kernel, the value -%ENODEV will be
> returned."
This check is not for the situation when the debugfs is not enabled.
But for if we failed in debugfs_init(), then
we should not use any API of debugfs.
And I think "-%ENODEV will be returned" means below code in "debugfs.h"
static inline struct dentry *debugfs_create_dir(const char *name,
struct dentry *parent)
{
return ERR_PTR(-ENODEV);
}
>
>> +
>> + 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?
Yes, you are right. -ENOMEM is not the only reason for the failure.
But debugfs_create_dir does not bring back the errno.
And for zsmalloc, we indeed have the permission(-EPERM) to create the entry and
also we will not create duplicate(-EEXIST) entry in debufs.
So, I think -ENOMEM is suitable.
>
>> +
>> + 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.
Yes, you are right.
>
>> +
>> + 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.
Got it. I will redo this.
>
>> + 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.
Thanks for your suggestion.
>
>> + 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?
It is better to check the return value and give user some information
about the failure.
>
>> +
>> +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());
Got it. thanks
>
>> }
>>
>> 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)
OK
>
>
>> /* 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)
OK
>
>> 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.
OK
>
>> +
>> + 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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