linux-kernel - Re: [PATCH 2/2] zram: idle memory tracking

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Date:   Tue, 27 Mar 2018 11:21:26 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] zram: idle memory tracking

On (03/26/18 15:49), Minchan Kim wrote:
[..]
> +static ssize_t read_access_time(struct file *file, char __user *buf,
> +				size_t count, loff_t *ppos)
> +{
[..]
> +
> +	for (index = *ppos; index < nr_pages; index++) {
> +		zram_slot_lock(zram, index);
> +		if (zram_test_flag(zram, index, ZRAM_WB))
> +			goto next;

I think it'll be better to show ZRAM_WB pages as well. Those pages
are swapped out pages after all, consuming swap space - a physical
page. Freeing those should also be beneficial. So tracking "bad"
incompressible pages is quite handful.

> +		if (zram_test_flag(zram, index, ZRAM_SAME))
> +			goto next;
> +		if (!zram_get_handle(zram, index))
> +			goto next;
> +
> +		ret = snprintf(kbuf + written, remained, "%lu %lu\n", index,
> +				get_seconds() - zram->table[index].ac_time);

So here you can add a flag after index and age which will tell if the page
is in zsmalloc pool or on backing swap device.

> +		if (remained < ret) {
> +			zram_slot_unlock(zram, index);
> +			break;
> +		}
> +		written += ret;
> +		remained -= ret;
> +next:
> +		zram_slot_unlock(zram, index);
> +		*ppos += 1;
> +	}
> +
> +	up_read(&zram->init_lock);
> +	copy_to_user(buf, kbuf, written);
> +	kvfree(kbuf);
> +
> +	return written;
> +}

	-ss