Re: [PATCH 2/2] mm/zsmalloc: add statistics support

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Hello, Minchan

2014-12-19 7:44 GMT+08:00 Minchan Kim <minchan@xxxxxxxxxx>:
> Hello Ganesh,
>
> On Wed, Dec 17, 2014 at 03:05:19PM +0800, Ganesh Mahendran wrote:
>> Hello, Minchan
>>
>> Thanks for your review.
>>
>> 2014-12-16 10:45 GMT+08:00 Minchan Kim <minchan@xxxxxxxxxx>:
>> > 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@xxxxxxxxx>
>> >> Suggested-by: Minchan Kim <minchan@xxxxxxxxxx>
>> >> ---
>> >>  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.
>
> It seems you are saying why debugfs_create_dir can fail but zsmalloc will not
> fail by such reasons.
> I don't know the internal of debugfs_create_dir but description just says
> "If an error occurs, %NULL will be returned" but everyone returns ENOMEM
> blindly then. Hmm, I don't think it's good but I'm okay too because it's not
> our fault and others have been in there. :(
>
> When I look at zs_init, you don't propagate the error to user. Just missing?

As the statistics collection is not essential to user, and I think we
do not need to break
the zsmalloc module loading when error happens in
zs_stat_init()/debugfs_create_dir().
So I do not propagate the error to user and just give the message:
       pr_warn("zs stat initialization failed\n");

Thanks.

>
>>
>> >
>> >> +
>> >> +     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
>> >>
>>
>> --
>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
>> the body to majordomo@xxxxxxxxx.  For more info on Linux MM,
>> see: http://www.linux-mm.org/ .
>> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
>
> --
> Kind regards,
> Minchan Kim

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