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    SubjectRe: [PATCH 06/10] Block discard support
    From
    On Mon, Aug 9, 2010 at 8:26 PM, Nitin Gupta <ngupta@vflare.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@vflare.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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