Decouple arc_read_done callback from arc buf instantiation
Add ARC_FLAG_NO_BUF to indicate that a buffer need not be instantiated. This fixes a ~20% performance regression on cached reads due to zfetch changes. Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Matthew Ahrens <mahrens@delphix.com> Signed-off-by: Matt Macy <mmacy@FreeBSD.org> Closes #11220 Closes #11232
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@ -154,6 +154,11 @@ typedef enum arc_flags
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*/
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ARC_FLAG_CACHED_ONLY = 1 << 22,
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/*
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* Don't instantiate an arc_buf_t for arc_read_done.
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*/
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ARC_FLAG_NO_BUF = 1 << 23,
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/*
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* The arc buffer's compression mode is stored in the top 7 bits of the
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* flags field, so these dummy flags are included so that MDB can
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@ -5924,6 +5924,7 @@ arc_read(zio_t *pio, spa_t *spa, const blkptr_t *bp,
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boolean_t noauth_read = BP_IS_AUTHENTICATED(bp) &&
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(zio_flags & ZIO_FLAG_RAW_ENCRYPT) != 0;
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boolean_t embedded_bp = !!BP_IS_EMBEDDED(bp);
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boolean_t no_buf = *arc_flags & ARC_FLAG_NO_BUF;
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int rc = 0;
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ASSERT(!embedded_bp ||
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@ -5998,7 +5999,7 @@ arc_read(zio_t *pio, spa_t *spa, const blkptr_t *bp,
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}
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ASSERT(*arc_flags & ARC_FLAG_NOWAIT);
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if (done) {
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if (done && !no_buf) {
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arc_callback_t *acb = NULL;
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acb = kmem_zalloc(sizeof (arc_callback_t),
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@ -6027,7 +6028,7 @@ arc_read(zio_t *pio, spa_t *spa, const blkptr_t *bp,
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ASSERT(hdr->b_l1hdr.b_state == arc_mru ||
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hdr->b_l1hdr.b_state == arc_mfu);
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if (done) {
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if (done && !no_buf) {
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if (hdr->b_flags & ARC_FLAG_PREDICTIVE_PREFETCH) {
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/*
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* This is a demand read which does not have to
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@ -3040,7 +3040,8 @@ dbuf_issue_final_prefetch(dbuf_prefetch_arg_t *dpa, blkptr_t *bp)
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int zio_flags = ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE;
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arc_flags_t aflags =
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dpa->dpa_aflags | ARC_FLAG_NOWAIT | ARC_FLAG_PREFETCH;
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dpa->dpa_aflags | ARC_FLAG_NOWAIT | ARC_FLAG_PREFETCH |
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ARC_FLAG_NO_BUF;
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/* dnodes are always read as raw and then converted later */
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if (BP_GET_TYPE(bp) == DMU_OT_DNODE && BP_IS_PROTECTED(bp) &&
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