On Mon, May 07, 2018 at 10:13:35AM -0600, Jens Axboe wrote:
> Throttle discards like we would any background write. Discards should
> be background activity, so if they are impacting foreground IO, then
> we will throttle them down.
>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--D
> ---
> block/blk-stat.h | 6 +++---
> block/blk-wbt.c | 43 ++++++++++++++++++++++++++-----------------
> block/blk-wbt.h | 4 +++-
> 3 files changed, 32 insertions(+), 21 deletions(-)
>
> diff --git a/block/blk-stat.h b/block/blk-stat.h
> index 2dd36347252a..c22049a8125e 100644
> --- a/block/blk-stat.h
> +++ b/block/blk-stat.h
> @@ -10,11 +10,11 @@
>
> /*
> * from upper:
> - * 3 bits: reserved for other usage
> + * 4 bits: reserved for other usage
> * 12 bits: size
> - * 49 bits: time
> + * 48 bits: time
> */
> -#define BLK_STAT_RES_BITS 3
> +#define BLK_STAT_RES_BITS 4
> #define BLK_STAT_SIZE_BITS 12
> #define BLK_STAT_RES_SHIFT (64 - BLK_STAT_RES_BITS)
> #define BLK_STAT_SIZE_SHIFT (BLK_STAT_RES_SHIFT - BLK_STAT_SIZE_BITS)
> diff --git a/block/blk-wbt.c b/block/blk-wbt.c
> index 25d202345965..a7a724580033 100644
> --- a/block/blk-wbt.c
> +++ b/block/blk-wbt.c
> @@ -106,6 +106,8 @@ static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb,
> {
> if (wb_acct & WBT_KSWAPD)
> return &rwb->rq_wait[WBT_RWQ_KSWAPD];
> + else if (wb_acct & WBT_DISCARD)
> + return &rwb->rq_wait[WBT_RWQ_DISCARD];
>
> return &rwb->rq_wait[WBT_RWQ_BG];
> }
> @@ -143,10 +145,13 @@ void __wbt_done(struct rq_wb *rwb, enum wbt_flags wb_acct)
> }
>
> /*
> - * If the device does write back caching, drop further down
> - * before we wake people up.
> + * For discards, our limit is always the background. For writes, if
> + * the device does write back caching, drop further down before we
> + * wake people up.
> */
> - if (rwb->wc && !wb_recent_wait(rwb))
> + if (wb_acct & WBT_DISCARD)
> + limit = rwb->wb_background;
> + else if (rwb->wc && !wb_recent_wait(rwb))
> limit = 0;
> else
> limit = rwb->wb_normal;
> @@ -483,6 +488,9 @@ static inline unsigned int get_limit(struct rq_wb *rwb, unsigned long rw)
> {
> unsigned int limit;
>
> + if ((rw & REQ_OP_MASK) == REQ_OP_DISCARD)
> + return rwb->wb_background;
> +
> /*
> * At this point we know it's a buffered write. If this is
> * kswapd trying to free memory, or REQ_SYNC is set, then
> @@ -564,21 +572,20 @@ static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct,
>
> static inline bool wbt_should_throttle(struct rq_wb *rwb, struct bio *bio)
> {
> - const int op = bio_op(bio);
> -
> - /*
> - * If not a WRITE, do nothing
> - */
> - if (op != REQ_OP_WRITE)
> - return false;
> -
> - /*
> - * Don't throttle WRITE_ODIRECT
> - */
> - if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) == (REQ_SYNC | REQ_IDLE))
> + switch (bio_op(bio)) {
> + case REQ_OP_WRITE:
> + /*
> + * Don't throttle WRITE_ODIRECT
> + */
> + if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) ==
> + (REQ_SYNC | REQ_IDLE))
> + return false;
> + /* fallthrough */
> + case REQ_OP_DISCARD:
> + return true;
> + default:
> return false;
> -
> - return true;
> + }
> }
>
> /*
> @@ -605,6 +612,8 @@ enum wbt_flags wbt_wait(struct rq_wb *rwb, struct bio *bio, spinlock_t *lock)
>
> if (current_is_kswapd())
> ret |= WBT_KSWAPD;
> + if (bio_op(bio) == REQ_OP_DISCARD)
> + ret |= WBT_DISCARD;
>
> __wbt_wait(rwb, ret, bio->bi_opf, lock);
>
> diff --git a/block/blk-wbt.h b/block/blk-wbt.h
> index 8038b4a0d4ef..d6a125e49db5 100644
> --- a/block/blk-wbt.h
> +++ b/block/blk-wbt.h
> @@ -14,13 +14,15 @@ enum wbt_flags {
> WBT_TRACKED = 1, /* write, tracked for throttling */
> WBT_READ = 2, /* read */
> WBT_KSWAPD = 4, /* write, from kswapd */
> + WBT_DISCARD = 8, /* discard */
>
> - WBT_NR_BITS = 3, /* number of bits */
> + WBT_NR_BITS = 4, /* number of bits */
> };
>
> enum {
> WBT_RWQ_BG = 0,
> WBT_RWQ_KSWAPD,
> + WBT_RWQ_DISCARD,
> WBT_NUM_RWQ,
> };
>
> --
> 2.7.4
>
> --
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