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5219 l2arc_write_buffers() may write beyond target_sz
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Saso Kiselkov <skiselkov@gmail.com>
Reviewed by: George Wilson <george@delphix.com>
Reviewed by: Steven Hartland <steven.hartland@multiplay.co.uk>
Reviewed by: Justin Gibbs <gibbs@FreeBSD.org>
Approved by: Matthew Ahrens <mahrens@delphix.com>
@@ -5842,11 +5842,11 @@
static uint64_t
l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz,
boolean_t *headroom_boost)
{
arc_buf_hdr_t *hdr, *hdr_prev, *head;
- uint64_t write_asize, write_psize, write_sz, headroom,
+ uint64_t write_asize, write_sz, headroom,
buf_compress_minsz;
void *buf_data;
boolean_t full;
l2arc_write_callback_t *cb;
zio_t *pio, *wzio;
@@ -5857,11 +5857,11 @@
/* Lower the flag now, we might want to raise it again later. */
*headroom_boost = B_FALSE;
pio = NULL;
- write_sz = write_asize = write_psize = 0;
+ write_sz = write_asize = 0;
full = B_FALSE;
head = kmem_cache_alloc(hdr_l2only_cache, KM_PUSHPAGE);
head->b_flags |= ARC_FLAG_L2_WRITE_HEAD;
head->b_flags |= ARC_FLAG_HAS_L2HDR;
@@ -5894,10 +5894,11 @@
headroom = (headroom * l2arc_headroom_boost) / 100;
for (; hdr; hdr = hdr_prev) {
kmutex_t *hash_lock;
uint64_t buf_sz;
+ uint64_t buf_a_sz;
if (arc_warm == B_FALSE)
hdr_prev = multilist_sublist_next(mls, hdr);
else
hdr_prev = multilist_sublist_prev(mls, hdr);
@@ -5922,11 +5923,19 @@
if (!l2arc_write_eligible(guid, hdr)) {
mutex_exit(hash_lock);
continue;
}
- if ((write_sz + hdr->b_size) > target_sz) {
+ /*
+ * Assume that the buffer is not going to be compressed
+ * and could take more space on disk because of a larger
+ * disk block size.
+ */
+ buf_sz = hdr->b_size;
+ buf_a_sz = vdev_psize_to_asize(dev->l2ad_vdev, buf_sz);
+
+ if ((write_asize + buf_a_sz) > target_sz) {
full = B_TRUE;
mutex_exit(hash_lock);
break;
}
@@ -5986,11 +5995,10 @@
* be holding the l2ad_mtx; which is why we're
* using it to denote the header's state change.
*/
hdr->b_l2hdr.b_daddr = L2ARC_ADDR_UNSET;
- buf_sz = hdr->b_size;
hdr->b_flags |= ARC_FLAG_HAS_L2HDR;
mutex_enter(&dev->l2ad_mtx);
list_insert_head(&dev->l2ad_buflist, hdr);
mutex_exit(&dev->l2ad_mtx);
@@ -6003,10 +6011,11 @@
arc_cksum_compute(hdr->b_l1hdr.b_buf, B_TRUE);
mutex_exit(hash_lock);
write_sz += buf_sz;
+ write_asize += buf_a_sz;
}
multilist_sublist_unlock(mls);
if (full == B_TRUE)
@@ -6022,10 +6031,23 @@
}
mutex_enter(&dev->l2ad_mtx);
/*
+ * Note that elsewhere in this file arcstat_l2_asize
+ * and the used space on l2ad_vdev are updated using b_asize,
+ * which is not necessarily rounded up to the device block size.
+ * Too keep accounting consistent we do the same here as well:
+ * stats_size accumulates the sum of b_asize of the written buffers,
+ * while write_asize accumulates the sum of b_asize rounded up
+ * to the device block size.
+ * The latter sum is used only to validate the corectness of the code.
+ */
+ uint64_t stats_size = 0;
+ write_asize = 0;
+
+ /*
* Now start writing the buffers. We're starting at the write head
* and work backwards, retracing the course of the buffer selector
* loop above.
*/
for (hdr = list_prev(&dev->l2ad_buflist, head); hdr;
@@ -6074,11 +6096,11 @@
*/
(void) refcount_add_many(&dev->l2ad_alloc, buf_sz, hdr);
/* Compression may have squashed the buffer to zero length. */
if (buf_sz != 0) {
- uint64_t buf_p_sz;
+ uint64_t buf_a_sz;
wzio = zio_write_phys(pio, dev->l2ad_vdev,
dev->l2ad_hand, buf_sz, buf_data, ZIO_CHECKSUM_OFF,
NULL, NULL, ZIO_PRIORITY_ASYNC_WRITE,
ZIO_FLAG_CANFAIL, B_FALSE);
@@ -6085,29 +6107,29 @@
DTRACE_PROBE2(l2arc__write, vdev_t *, dev->l2ad_vdev,
zio_t *, wzio);
(void) zio_nowait(wzio);
- write_asize += buf_sz;
+ stats_size += buf_sz;
/*
* Keep the clock hand suitably device-aligned.
*/
- buf_p_sz = vdev_psize_to_asize(dev->l2ad_vdev, buf_sz);
- write_psize += buf_p_sz;
- dev->l2ad_hand += buf_p_sz;
+ buf_a_sz = vdev_psize_to_asize(dev->l2ad_vdev, buf_sz);
+ write_asize += buf_a_sz;
+ dev->l2ad_hand += buf_a_sz;
}
}
mutex_exit(&dev->l2ad_mtx);
ASSERT3U(write_asize, <=, target_sz);
ARCSTAT_BUMP(arcstat_l2_writes_sent);
ARCSTAT_INCR(arcstat_l2_write_bytes, write_asize);
ARCSTAT_INCR(arcstat_l2_size, write_sz);
- ARCSTAT_INCR(arcstat_l2_asize, write_asize);
- vdev_space_update(dev->l2ad_vdev, write_asize, 0, 0);
+ ARCSTAT_INCR(arcstat_l2_asize, stats_size);
+ vdev_space_update(dev->l2ad_vdev, stats_size, 0, 0);
/*
* Bump device hand to the device start if it is approaching the end.
* l2arc_evict() will already have evicted ahead for this case.
*/