Hello,
On (02/26/14 14:23), Joonsoo Kim wrote:
> zram is ram based block device and can be used by backend of filesystem.
> When filesystem deletes a file, it normally doesn't do anything on data
> block of that file. It just marks on metadata of that file. This behavior
> has no problem on disk based block device, but has problems on ram based
> block device, since we can't free memory used for data block. To overcome
> this disadvantage, there is REQ_DISCARD functionality. If block device
> support REQ_DISCARD and filesystem is mounted with discard option,
> filesystem sends REQ_DISCARD to block device whenever some data blocks are
> discarded. All we have to do is to handle this request.
>
> This patch implements to flag up QUEUE_FLAG_DISCARD and handle this
> REQ_DISCARD request. With it, we can free memory used by zram if it isn't
> used.
>
> v2: handle unaligned case commented by Jerome
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo....@lge.com>
>
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 5ec61be..5364c1e 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -501,6 +501,36 @@ static int zram_bvec_rw(struct zram *zram, struct
> bio_vec *bvec, u32 index,
> return ret;
> }
>
> +static void zram_bio_discard(struct zram *zram, struct bio *bio)
> +{
> + u32 index = bio->bi_iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
> + size_t n = bio->bi_iter.bi_size;
> + size_t misalign;
> +
> + /*
> + * On some arch, logical block (4096) aligned request couldn't be
> + * aligned to PAGE_SIZE, since their PAGE_SIZE aren't 4096.
> + * Therefore we should handle this misaligned case here.
> + */
> + misalign = (bio->bi_iter.bi_sector &
> + (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT;
> + if (misalign) {
> + if (n < misalign)
> + return;
> +
> + n -= misalign;
> + index++;
> + }
> +
> + while (n >= PAGE_SIZE) {
> + write_lock(&zram->meta->tb_lock);
> + zram_free_page(zram, index);
> + write_unlock(&zram->meta->tb_lock);
> + index++;
> + n -= PAGE_SIZE;
> + }
> +}
> +
a side note, do we need zram_bio_discard() function? I mean, can we handle
discard request in zram_bvec_rw(), where we already know index, etc. (passed
from __zram_make_request())?
for example:
@@ -510,6 +510,11 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec
*bvec, u32 index,
ret = zram_bvec_write(zram, bvec, index, offset);
}
+ if (unlikely(bio->bi_rw & REQ_DISCARD)) {
+ write_lock(&zram->meta->tb_lock);
+ zram_free_page(zram, index);
+ write_unlock(&zram->meta->tb_lock);
+ }
return ret;
}
-ss
> static void zram_reset_device(struct zram *zram, bool reset_capacity)
> {
> size_t index;
> @@ -618,6 +648,12 @@ static void __zram_make_request(struct zram *zram,
> struct bio *bio)
> struct bio_vec bvec;
> struct bvec_iter iter;
>
> + if (unlikely(bio->bi_rw & REQ_DISCARD)) {
> + zram_bio_discard(zram, bio);
> + bio_endio(bio, 0);
> + return;
> + }
> +
> index = bio->bi_iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
> offset = (bio->bi_iter.bi_sector &
> (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT;
> @@ -784,6 +820,10 @@ static int create_device(struct zram *zram, int
> device_id)
> ZRAM_LOGICAL_BLOCK_SIZE);
> 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->disk->queue);
>
> add_disk(zram->disk);
>
> --
> 1.7.9.5
>
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