On Mon, Jul 06, 2015 at 09:17:49PM +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 `num_compacted'
> column in zram<id>/mm_stat represents more meaningful value:
> the number of freed (compacted) pages.
Fair enough.
The main reason I introduced num_migrated is to investigate
the effieciency of compaction. ie, num_freed / num_migrated.
However, I didn't put num_freed at that time so I can't get
my goal with only num_migrated.
We could put new knob num_compacted as well as num_migrated
but I don't think we need it now. Zram's compaction would be
much efficient compared to VM's compaction because we don't
have any non-movable objects in zspages and we can account
exact number of free slots.
So, I want to change name from num_migrated to num_compacted
and maintain only it which is more useful for admin, you said.
It's not far since we introduced num_migrated so I don't think
change name wouldn't be a big problem for userspace,(I hope).
>
> Return first_page's fullness_group from putback_zspage(),
> so we now for sure know that putback_zspage() has issued
> free_zspage() and we must update compaction stats.
>
> Update documentation.
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> ---
> Documentation/blockdev/zram.txt | 3 ++-
> mm/zsmalloc.c | 27 +++++++++++++++++----------
> 2 files changed, 19 insertions(+), 11 deletions(-)
>
> diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
> index c4de576..71f4744 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
> +num_migrated 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/mm/zsmalloc.c b/mm/zsmalloc.c
> index e0f508a..a761733 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -245,7 +245,7 @@ struct zs_pool {
> /* Allocation flags used when growing pool */
> gfp_t flags;
> atomic_long_t pages_allocated;
> - /* How many objects were migrated */
> + /* How many pages were migrated (freed) */
> unsigned long num_migrated;
>
> #ifdef CONFIG_ZSMALLOC_STAT
> @@ -1596,8 +1596,6 @@ 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,
> @@ -1634,7 +1632,6 @@ 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 */
> @@ -1660,8 +1657,17 @@ 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;
>
> @@ -1679,6 +1685,8 @@ 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)
> @@ -1720,7 +1728,6 @@ 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))) {
>
> @@ -1749,7 +1756,9 @@ 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->num_migrated +=
> + get_pages_per_zspage(class->size);
> spin_unlock(&class->lock);
> cond_resched();
> spin_lock(&class->lock);
> @@ -1758,8 +1767,6 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
> if (src_page)
> putback_zspage(pool, class, src_page);
>
> - pool->num_migrated += cc.nr_migrated;
> -
> spin_unlock(&class->lock);
> }
>
> --
> 2.5.0.rc0.3.g912bd49
>
--
Kind regards,
Minchan Kim
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