Re: [PATCH v2] zsmalloc: zs_page_migrate: schedule free_work if zspage is ZS_EMPTY

[Minchan Kim <minchan@kernel.org>]

Hi Hui,

On Mon, Aug 14, 2017 at 05:56:30PM +0800, Hui Zhu wrote:
> After commit e2846124f9a2 ("zsmalloc: zs_page_migrate: skip unnecessary

This patch is not merged yet so the hash is invalid.
That means we may fold this patch to [1] in current mmotm.

[1] zsmalloc-zs_page_migrate-skip-unnecessary-loops-but-not-return-ebusy-if-zspage-is-not-inuse-fix.patch

> loops but not return -EBUSY if zspage is not inuse") zs_page_migrate
> can handle the ZS_EMPTY zspage.
> 
> But I got some false in zs_page_isolate:
> 	if (get_zspage_inuse(zspage) == 0) {
> 		spin_unlock(&class->lock);
> 		return false;
> 	}

I also realized we should make zs_page_isolate succeed on empty zspage
because we allow the empty zspage migration from now on.
Could you send a patch for that as well?

> The page of this zspage was migrated in before.
> 
> The reason is commit e2846124f9a2 ("zsmalloc: zs_page_migrate: skip
> unnecessary loops but not return -EBUSY if zspage is not inuse") just
> handle the "page" but not "newpage" then it keep the "newpage" with
> a empty zspage inside system.
> Root cause is zs_page_isolate remove it from ZS_EMPTY list but not
> call zs_page_putback "schedule_work(&pool->free_work);".  Because
> zs_page_migrate done the job without "schedule_work(&pool->free_work);"
> 
> Make this patch let zs_page_migrate wake up free_work if need.
> 
> Fixes: e2846124f9a2 ("zsmalloc: zs_page_migrate: skip unnecessary loops but not return -EBUSY if zspage is not inuse")
> Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
> ---
>  mm/zsmalloc.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 62457eb..c6cc77c 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -2035,8 +2035,17 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
>  	 * Page migration is done so let's putback isolated zspage to
>  	 * the list if @page is final isolated subpage in the zspage.
>  	 */
> -	if (!is_zspage_isolated(zspage))
> -		putback_zspage(class, zspage);
> +	if (!is_zspage_isolated(zspage)) {
> +		/*
> +		 * Page will be freed in following part. But newpage and
> +		 * zspage will stay in system if zspage is in ZS_EMPTY
> +		 * list.  So call free_work to free it.
> +		 * The page and class is locked, we cannot free zspage
> +		 * immediately so let's defer.
> +		 */

How about this?

                /*
                 * Since we allow empty zspage migration, putback of zspage
                 * should free empty zspage. Otherwise, it could make a leak
                 * until upcoming free_work is done, which isn't guaranteed.
                 */
> +		if (putback_zspage(class, zspage) == ZS_EMPTY)
> +			schedule_work(&pool->free_work);
> +	}
>  
>  	reset_page(page);
>  	put_page(page);
> -- 
> 1.9.1
> 
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