blk-wbt: throttle discards like background writes
authorJens Axboe <axboe@kernel.dk>
Mon, 7 May 2018 16:03:23 +0000 (10:03 -0600)
committerJens Axboe <axboe@kernel.dk>
Tue, 8 May 2018 21:11:02 +0000 (15:11 -0600)
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.

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
block/blk-stat.h
block/blk-wbt.c
block/blk-wbt.h

index 2dd3634..c22049a 100644 (file)
 
 /*
  * 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)
index 25d2023..a7a7245 100644 (file)
@@ -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);
 
index 8038b4a..d6a125e 100644 (file)
@@ -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,
 };