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

From: Minchan Kim
Date: Thu Dec 18 2014 - 20:29:00 EST

On Fri, Dec 19, 2014 at 09:21:52AM +0800, Ganesh Mahendran wrote:
> 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");

Hmm? So you want to work without stat although user want?
It means every zs_stat_[inc|dec] should check if it was initialized properly?

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

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Kind regards,
Minchan Kim
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