Re: [PATCH v3] zram: Introduce an aged idle interface

[Minchan Kim]

On Tue, Sep 21, 2021 at 12:43:36PM -0700, Brian Geffon wrote:
> This change introduces an aged idle interface to the existing
> idle sysfs file for zram.
> 
> When CONFIG_ZRAM_MEMORY_TRACKING is enabled the idle file
> now also accepts an integer argument. This integer is the
> age (in seconds) of pages to mark as idle. The idle file
> still supports 'all' as it always has. This new approach
> allows for much more control over which pages get marked
> as idle.
> 
>   v2 -> v3:
> 	- Correct unused variable warning when
> 	  CONFIG_ZRAM_MEMORY_TRACKING is not enabled.
>   v1 -> v2:
> 	- Switch to using existing idle file.
> 	- Dont compare ktime directly.
> 
> Signed-off-by: Brian Geffon <bgeffon@xxxxxxxxxx>
> ---
>  Documentation/admin-guide/blockdev/zram.rst |  8 +++
>  drivers/block/zram/zram_drv.c               | 60 +++++++++++++++------
>  2 files changed, 52 insertions(+), 16 deletions(-)
> 
> diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
> index 700329d25f57..8c8a92e5c00c 100644
> --- a/Documentation/admin-guide/blockdev/zram.rst
> +++ b/Documentation/admin-guide/blockdev/zram.rst
> @@ -328,6 +328,14 @@ as idle::
>  From now on, any pages on zram are idle pages. The idle mark
>  will be removed until someone requests access of the block.
>  IOW, unless there is access request, those pages are still idle pages.
> +Additionally, when CONFIG_ZRAM_MEMORY_TRACKING is enabled pages can be
> +marked as idle based on how long (in seconds) it's been since they were
> +last accessed, in seconds::
> +
> +        echo 86400 > /sys/block/zramX/idle
> +
> +In this example all pages which haven't been accessed in more than 86400
> +seconds (one day) will be marked idle.
>  
>  Admin can request writeback of those idle pages at right timing via::
>  
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index fcaf2750f68f..2af5cdb8da1a 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -291,22 +291,16 @@ static ssize_t mem_used_max_store(struct device *dev,
>  	return len;
>  }
>  
> -static ssize_t idle_store(struct device *dev,
> -		struct device_attribute *attr, const char *buf, size_t len)
> +/*
> + * Mark all pages which are older than or equal to cutoff as IDLE.
> + * Callers should hold the zram init lock in read mode
> + **/
> +static void mark_idle(struct zram *zram, ktime_t cutoff)
>  {
> -	struct zram *zram = dev_to_zram(dev);
> +	int is_idle = 1;
>  	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
>  	int index;
>  
> -	if (!sysfs_streq(buf, "all"))
> -		return -EINVAL;
> -
> -	down_read(&zram->init_lock);
> -	if (!init_done(zram)) {
> -		up_read(&zram->init_lock);
> -		return -EINVAL;
> -	}
> -
>  	for (index = 0; index < nr_pages; index++) {
>  		/*
>  		 * Do not mark ZRAM_UNDER_WB slot as ZRAM_IDLE to close race.
> @@ -314,14 +308,48 @@ static ssize_t idle_store(struct device *dev,
>  		 */
>  		zram_slot_lock(zram, index);
>  		if (zram_allocated(zram, index) &&
> -				!zram_test_flag(zram, index, ZRAM_UNDER_WB))
> -			zram_set_flag(zram, index, ZRAM_IDLE);
> +				!zram_test_flag(zram, index, ZRAM_UNDER_WB)) {
> +#ifdef CONFIG_ZRAM_MEMORY_TRACKING
> +			is_idle = (!cutoff || ktime_after(cutoff, zram->table[index].ac_time));
> +#endif
> +			if (is_idle)
> +				zram_set_flag(zram, index, ZRAM_IDLE);
> +		}
>  		zram_slot_unlock(zram, index);
>  	}
> +}
>  
> -	up_read(&zram->init_lock);
> +static ssize_t idle_store(struct device *dev,
> +		struct device_attribute *attr, const char *buf, size_t len)
> +{
> +	struct zram *zram = dev_to_zram(dev);
> +	ktime_t cutoff_time = 0;
> +	ssize_t rv = -EINVAL;
>  
> -	return len;
> +	if (!sysfs_streq(buf, "all")) {
> +#ifdef CONFIG_ZRAM_MEMORY_TRACKING
> +		u64 age_sec;
> +		/* If it did not parse as 'all' try to treat it as an integer */
> +		if (!kstrtoull(buf, 10, &age_sec))

nit:
Do we need such limit base which work with only 10 base?
Passing 0 would give more flexibility. 

Otherwise, looks good to me.

Thanks, Brian.

> +			cutoff_time = ktime_sub(ktime_get_boottime(),
> +					ns_to_ktime(age_sec * NSEC_PER_SEC));
> +		else
> +#endif
> +			goto out;
> +	}
> +
> +	down_read(&zram->init_lock);
> +	if (!init_done(zram))
> +		goto out_unlock;
> +
> +	/* A age_sec of 0 marks everything as idle, this is the "all" behavior */
> +	mark_idle(zram, cutoff_time);
> +	rv = len;
> +
> +out_unlock:
> +	up_read(&zram->init_lock);
> +out:
> +	return rv;
>  }
>  
>  #ifdef CONFIG_ZRAM_WRITEBACK
> -- 
> 2.33.0.464.g1972c5931b-goog
>