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Date: Tue, 7 Jul 2015 22:39:16 +0900
From: Minchan Kim <minchan@...nel.org>
To: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH v6 6/7] zsmalloc: account the number of compacted pages
On Tue, Jul 07, 2015 at 08:57:00PM +0900, Sergey Senozhatsky wrote:
> Compaction returns back to zram the number of migrated objects,
> which is quite uninformative -- we have objects of different
> sizes so user space cannot obtain any valuable data from that
> number. Change compaction to operate in terms of pages and
> return back to compaction issuer the number of pages that
> were freed during compaction. So from now on we will export
> more meaningful value in zram<id>/mm_stat -- the number of freed
> (compacted) pages.
>
> This requires:
> (a) a rename of `num_migrated' to 'pages_compacted'
> (b) a internal API change -- return first_page's fullness_group
> from putback_zspage(), so we know when putback_zspage() did
> free_zspage(). It helps us to account compaction stats correctly.
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Acked-by: Minchan Kim <minchan@...nel.org>
A nit below.
> ---
> Documentation/blockdev/zram.txt | 3 ++-
> drivers/block/zram/zram_drv.c | 2 +-
> include/linux/zsmalloc.h | 4 ++--
> mm/zsmalloc.c | 27 +++++++++++++++++----------
> 4 files changed, 22 insertions(+), 14 deletions(-)
>
> diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
> index c4de576..62435bb 100644
> --- a/Documentation/blockdev/zram.txt
> +++ b/Documentation/blockdev/zram.txt
> @@ -144,7 +144,8 @@ mem_used_max RW the maximum amount memory zram have consumed to
> store compressed data
> mem_limit RW the maximum amount of memory ZRAM can use to store
> the compressed data
> -num_migrated RO the number of objects migrated migrated by compaction
> +pages_compacted RO the number of pages freed during compaction
> + (available only via zram<id>/mm_stat node)
> compact WO trigger memory compaction
>
> WARNING
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index aa22fe07..1bcbc19 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -448,7 +448,7 @@ static ssize_t mm_stat_show(struct device *dev,
> zram->limit_pages << PAGE_SHIFT,
> max_used << PAGE_SHIFT,
> (u64)atomic64_read(&zram->stats.zero_pages),
> - pool_stats.num_migrated);
> + pool_stats.pages_compacted);
> up_read(&zram->init_lock);
>
> return ret;
> diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h
> index 9340fce..cda4ad4 100644
> --- a/include/linux/zsmalloc.h
> +++ b/include/linux/zsmalloc.h
> @@ -35,8 +35,8 @@ enum zs_mapmode {
> };
>
> struct zs_pool_stats {
> - /* How many objects were migrated */
> - u64 num_migrated;
> + /* How many pages were migrated (freed) */
> + u64 pages_compacted;
Hmm, if we account it as page unit, unsigned long is enough for 32bit.
> };
>
> struct zs_pool;
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index db3cb2d..13f2c4a 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1589,8 +1589,6 @@ struct zs_compact_control {
> /* Starting object index within @s_page which used for live object
> * in the subpage. */
> int index;
> - /* How many of objects were migrated */
> - int nr_migrated;
> };
>
> static int migrate_zspage(struct zs_pool *pool, struct size_class *class,
> @@ -1627,7 +1625,6 @@ static int migrate_zspage(struct zs_pool *pool, struct size_class *class,
> record_obj(handle, free_obj);
> unpin_tag(handle);
> obj_free(pool, class, used_obj);
> - cc->nr_migrated++;
> }
>
> /* Remember last position in this iteration */
> @@ -1653,8 +1650,17 @@ static struct page *isolate_target_page(struct size_class *class)
> return page;
> }
>
> -static void putback_zspage(struct zs_pool *pool, struct size_class *class,
> - struct page *first_page)
> +/*
> + * putback_zspage - add @first_page into right class's fullness list
> + * @pool: target pool
> + * @class: destination class
> + * @first_page: target page
> + *
> + * Return @fist_page's fullness_group
> + */
> +static enum fullness_group putback_zspage(struct zs_pool *pool,
> + struct size_class *class,
> + struct page *first_page)
> {
> enum fullness_group fullness;
>
> @@ -1672,6 +1678,8 @@ static void putback_zspage(struct zs_pool *pool, struct size_class *class,
>
> free_zspage(first_page);
> }
> +
> + return fullness;
> }
>
> static struct page *isolate_source_page(struct size_class *class)
> @@ -1713,7 +1721,6 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
> struct page *src_page;
> struct page *dst_page = NULL;
>
> - cc.nr_migrated = 0;
> spin_lock(&class->lock);
> while ((src_page = isolate_source_page(class))) {
>
> @@ -1742,7 +1749,9 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
> break;
>
> putback_zspage(pool, class, dst_page);
> - putback_zspage(pool, class, src_page);
> + if (putback_zspage(pool, class, src_page) == ZS_EMPTY)
> + pool->stats.pages_compacted +=
> + get_pages_per_zspage(class->size);
> spin_unlock(&class->lock);
> cond_resched();
> spin_lock(&class->lock);
> @@ -1751,8 +1760,6 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
> if (src_page)
> putback_zspage(pool, class, src_page);
>
> - pool->stats.num_migrated += cc.nr_migrated;
> -
> spin_unlock(&class->lock);
> }
>
> @@ -1770,7 +1777,7 @@ unsigned long zs_compact(struct zs_pool *pool)
> __zs_compact(pool, class);
> }
>
> - return pool->stats.num_migrated;
> + return pool->stats.pages_compacted;
> }
> EXPORT_SYMBOL_GPL(zs_compact);
>
> --
> 2.4.5
>
--
Kind regards,
Minchan Kim
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