From bc77a0c85ec9a26452992421f738dee0a786322b Mon Sep 17 00:00:00 2001
From: Alexander Motin <mav@FreeBSD.org>
Date: Wed, 4 Oct 2023 17:45:00 -0400
Subject: [PATCH] ARC: Remove b_cv from struct l1arc_buf_hdr
Earlier as part of #14123 I've removed one use of b_cv. This patch
reuses the same approach to remove the other one from much more
rare code path.
This saves 16 bytes of L1 ARC header on FreeBSD (reducing it from
200 to 184 bytes) and seems even more on Linux.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored by: iXsystems, Inc.
Closes #15340
---
include/sys/arc_impl.h | 2 --
module/zfs/arc.c | 34 ++++++++++++++++++++++------------
2 files changed, 22 insertions(+), 14 deletions(-)
diff --git a/include/sys/arc_impl.h b/include/sys/arc_impl.h
index 78774792f3..da07fd4f8f 100644
--- a/include/sys/arc_impl.h
+++ b/include/sys/arc_impl.h
@@ -159,8 +159,6 @@ struct arc_write_callback {
* these two allocation states.
*/
typedef struct l1arc_buf_hdr {
- /* for waiting on reads to complete */
- kcondvar_t b_cv;
uint8_t b_byteswap;
/* protected by arc state mutex */
diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index 22dc0ed5e3..919684a589 100644
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -1151,7 +1151,6 @@ hdr_full_cons(void *vbuf, void *unused, int kmflag)
memset(hdr, 0, HDR_FULL_SIZE);
hdr->b_l1hdr.b_byteswap = DMU_BSWAP_NUMFUNCS;
- cv_init(&hdr->b_l1hdr.b_cv, NULL, CV_DEFAULT, NULL);
zfs_refcount_create(&hdr->b_l1hdr.b_refcnt);
#ifdef ZFS_DEBUG
mutex_init(&hdr->b_l1hdr.b_freeze_lock, NULL, MUTEX_DEFAULT, NULL);
@@ -1211,7 +1210,6 @@ hdr_full_dest(void *vbuf, void *unused)
arc_buf_hdr_t *hdr = vbuf;
ASSERT(HDR_EMPTY(hdr));
- cv_destroy(&hdr->b_l1hdr.b_cv);
zfs_refcount_destroy(&hdr->b_l1hdr.b_refcnt);
#ifdef ZFS_DEBUG
mutex_destroy(&hdr->b_l1hdr.b_freeze_lock);
@@ -5586,13 +5584,6 @@ arc_read_done(zio_t *zio)
buf_hash_remove(hdr);
}
- /*
- * Broadcast before we drop the hash_lock to avoid the possibility
- * that the hdr (and hence the cv) might be freed before we get to
- * the cv_broadcast().
- */
- cv_broadcast(&hdr->b_l1hdr.b_cv);
-
arc_hdr_clear_flags(hdr, ARC_FLAG_IO_IN_PROGRESS);
(void) remove_reference(hdr, hdr);
@@ -5787,8 +5778,7 @@ top:
}
acb->acb_zio_head = head_zio;
acb->acb_next = hdr->b_l1hdr.b_acb;
- if (hdr->b_l1hdr.b_acb)
- hdr->b_l1hdr.b_acb->acb_prev = acb;
+ hdr->b_l1hdr.b_acb->acb_prev = acb;
hdr->b_l1hdr.b_acb = acb;
}
mutex_exit(hash_lock);
@@ -5928,8 +5918,28 @@ top:
* and so the performance impact shouldn't
* matter.
*/
- cv_wait(&hdr->b_l1hdr.b_cv, hash_lock);
+ arc_callback_t *acb = kmem_zalloc(
+ sizeof (arc_callback_t), KM_SLEEP);
+ acb->acb_wait = B_TRUE;
+ mutex_init(&acb->acb_wait_lock, NULL,
+ MUTEX_DEFAULT, NULL);
+ cv_init(&acb->acb_wait_cv, NULL, CV_DEFAULT,
+ NULL);
+ acb->acb_zio_head =
+ hdr->b_l1hdr.b_acb->acb_zio_head;
+ acb->acb_next = hdr->b_l1hdr.b_acb;
+ hdr->b_l1hdr.b_acb->acb_prev = acb;
+ hdr->b_l1hdr.b_acb = acb;
mutex_exit(hash_lock);
+ mutex_enter(&acb->acb_wait_lock);
+ while (acb->acb_wait) {
+ cv_wait(&acb->acb_wait_cv,
+ &acb->acb_wait_lock);
+ }
+ mutex_exit(&acb->acb_wait_lock);
+ mutex_destroy(&acb->acb_wait_lock);
+ cv_destroy(&acb->acb_wait_cv);
+ kmem_free(acb, sizeof (arc_callback_t));
goto top;
}
}