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Message-ID: <20141218234455.GA1538@bbox>
Date: Fri, 19 Dec 2014 08:44:55 +0900
From: Minchan Kim <minchan@...nel.org>
To: Ganesh Mahendran <opensource.ganesh@...il.com>
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 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@...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.
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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