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Date:	Wed, 17 Sep 2014 10:19:29 +0200
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Minchan Kim <minchan@...nel.org>, Nitin Gupta <ngupta@...are.org>,
	Chao Yu <chao2.yu@...sung.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3] zram: use notify_free to account all free notifications

On 09/15/2014 04:49 PM, Sergey Senozhatsky wrote:
> `notify_free' device attribute accounts the number of slot free notifications
> and internally represents the number of zram_free_page() calls. Slot free
> notifications are sent only when device is used as a swap device, hence
> `notify_free' is used only for swap devices. Since f4659d8e620d08 (zram:
> support REQ_DISCARD) ZRAM handles yet another one free notification (also
> via zram_free_page() call) -- REQ_DISCARD requests, which are sent by a
> filesystem, whenever some data blocks are discarded. However, there is no
> way to know the number of notifications in the latter case.
> 
> Use `notify_free' to account the number of pages freed by zram_bio_discard()
> and zram_slot_free_notify(). Depending on usage scenario `notify_free'
> represents:
>  a) the number of pages freed because of slot free notifications, which is
>    equal to the number of swap_slot_free_notify() calls, so there is no
>    behaviour change
> 
>  b) the number of pages freed because of REQ_DISCARD notifications
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

Acked-by: Jerome Marchand <jmarchan@...hat.com>

> ---
>  Documentation/ABI/testing/sysfs-block-zram | 13 ++++++++-----
>  drivers/block/zram/zram_drv.c              |  1 +
>  2 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram
> index b13dc99..a6148ea 100644
> --- a/Documentation/ABI/testing/sysfs-block-zram
> +++ b/Documentation/ABI/testing/sysfs-block-zram
> @@ -77,11 +77,14 @@ What:		/sys/block/zram<id>/notify_free
>  Date:		August 2010
>  Contact:	Nitin Gupta <ngupta@...are.org>
>  Description:
> -		The notify_free file is read-only and specifies the number of
> -		swap slot free notifications received by this device. These
> -		notifications are sent to a swap block device when a swap slot
> -		is freed. This statistic is applicable only when this disk is
> -		being used as a swap disk.
> +		The notify_free file is read-only. Depending on device usage
> +		scenario it may account a) the number of pages freed because
> +		of swap slot free notifications or b) the number of pages freed
> +		because of REQ_DISCARD requests sent by bio. The former ones
> +		are sent to a swap block device when a swap slot is freed, which
> +		implies that this disk is being used as a swap disk. The latter
> +		ones are sent by filesystem mounted with discard option,
> +		whenever some data blocks are getting discarded.
>  
>  What:		/sys/block/zram<id>/zero_pages
>  Date:		August 2010
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index d78b245..3b85016 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -698,6 +698,7 @@ static void zram_bio_discard(struct zram *zram, u32 index,
>  		bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
>  		zram_free_page(zram, index);
>  		bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
> +		atomic64_inc(&zram->stats.notify_free);
>  		index++;
>  		n -= PAGE_SIZE;
>  	}
> 



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