linux-kernel - Re: [PATCH 06/10] Block discard support

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Message-ID: <AANLkTimtdLb4Mk81fmCwksPR0GbTEaGZbo888OFefjXK@mail.gmail.com>
Date:	Mon, 9 Aug 2010 22:03:50 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Nitin Gupta <ngupta@...are.org>
Cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <greg@...ah.com>,
	Linux Driver Project <devel@...uxdriverproject.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, jaxboe@...ionio.com
Subject: Re: [PATCH 06/10] Block discard support

On Mon, Aug 9, 2010 at 8:26 PM, Nitin Gupta <ngupta@...are.org> wrote:
> The 'discard' bio discard request provides information to
> zram disks regarding blocks which are no longer in use by
> filesystem. This allows freeing memory allocated for such
> blocks.
>
> When zram devices are used as swap disks, we already have
> a callback (block_device_operations->swap_slot_free_notify).
> So, the discard support is useful only when used as generic
> (non-swap) disk.
>
> Signed-off-by: Nitin Gupta <ngupta@...are.org>

Lets CC fsdevel and Jens for this.

> ---
>  drivers/staging/zram/zram_drv.c   |   25 +++++++++++++++++++++++++
>  drivers/staging/zram/zram_sysfs.c |   11 +++++++++++
>  2 files changed, 36 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index efe9c93..0f9785f 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -420,6 +420,20 @@ out:
>        return 0;
>  }
>
> +static void zram_discard(struct zram *zram, struct bio *bio)
> +{
> +       size_t bytes = bio->bi_size;
> +       sector_t sector = bio->bi_sector;
> +
> +       while (bytes >= PAGE_SIZE) {
> +               zram_free_page(zram, sector >> SECTORS_PER_PAGE_SHIFT);
> +               sector += PAGE_SIZE >> SECTOR_SHIFT;
> +               bytes -= PAGE_SIZE;
> +       }
> +
> +       bio_endio(bio, 0);
> +}
> +
>  /*
>  * Check if request is within bounds and page aligned.
>  */
> @@ -451,6 +465,12 @@ static int zram_make_request(struct request_queue *queue, struct bio *bio)
>                return 0;
>        }
>
> +       if (unlikely(bio_rw_flagged(bio, BIO_RW_DISCARD))) {
> +               zram_inc_stat(zram, ZRAM_STAT_DISCARD);
> +               zram_discard(zram, bio);
> +               return 0;
> +       }
> +
>        switch (bio_data_dir(bio)) {
>        case READ:
>                ret = zram_read(zram, bio);
> @@ -606,6 +626,11 @@ static int create_device(struct zram *zram, int device_id)
>        blk_queue_io_min(zram->disk->queue, PAGE_SIZE);
>        blk_queue_io_opt(zram->disk->queue, PAGE_SIZE);
>
> +       zram->disk->queue->limits.discard_granularity = PAGE_SIZE;
> +       zram->disk->queue->limits.max_discard_sectors = UINT_MAX;
> +       zram->disk->queue->limits.discard_zeroes_data = 1;
> +       queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, zram->queue);
> +
>        add_disk(zram->disk);
>
>  #ifdef CONFIG_SYSFS
> diff --git a/drivers/staging/zram/zram_sysfs.c b/drivers/staging/zram/zram_sysfs.c
> index 43bcdd4..74971c0 100644
> --- a/drivers/staging/zram/zram_sysfs.c
> +++ b/drivers/staging/zram/zram_sysfs.c
> @@ -165,6 +165,15 @@ static ssize_t notify_free_show(struct device *dev,
>                zram_get_stat(zram, ZRAM_STAT_NOTIFY_FREE));
>  }
>
> +static ssize_t discard_show(struct device *dev,
> +               struct device_attribute *attr, char *buf)
> +{
> +       struct zram *zram = dev_to_zram(dev);
> +
> +       return sprintf(buf, "%llu\n",
> +               zram_get_stat(zram, ZRAM_STAT_DISCARD));
> +}
> +
>  static ssize_t zero_pages_show(struct device *dev,
>                struct device_attribute *attr, char *buf)
>  {
> @@ -215,6 +224,7 @@ static DEVICE_ATTR(num_reads, S_IRUGO, num_reads_show, NULL);
>  static DEVICE_ATTR(num_writes, S_IRUGO, num_writes_show, NULL);
>  static DEVICE_ATTR(invalid_io, S_IRUGO, invalid_io_show, NULL);
>  static DEVICE_ATTR(notify_free, S_IRUGO, notify_free_show, NULL);
> +static DEVICE_ATTR(discard, S_IRUGO, discard_show, NULL);
>  static DEVICE_ATTR(zero_pages, S_IRUGO, zero_pages_show, NULL);
>  static DEVICE_ATTR(orig_data_size, S_IRUGO, orig_data_size_show, NULL);
>  static DEVICE_ATTR(compr_data_size, S_IRUGO, compr_data_size_show, NULL);
> @@ -228,6 +238,7 @@ static struct attribute *zram_disk_attrs[] = {
>        &dev_attr_num_writes.attr,
>        &dev_attr_invalid_io.attr,
>        &dev_attr_notify_free.attr,
> +       &dev_attr_discard.attr,
>        &dev_attr_zero_pages.attr,
>        &dev_attr_orig_data_size.attr,
>        &dev_attr_compr_data_size.attr,
> --
> 1.7.2.1
>
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