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

[Minchan Kim]

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?

> 
> >
> >> +
> >> +     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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-- 
Kind regards,
Minchan Kim
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