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[after ARC lock-contention fixes] account for ashift when gathering buffers to be written to l2arc device #3491

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[after ARC lock-contention fixes] account for ashift when gathering buffers to be written to l2arc device #3491

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47 changes: 35 additions & 12 deletions module/zfs/arc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -5723,8 +5723,8 @@ 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,
buf_compress_minsz;
uint64_t write_asize, write_sz, headroom, buf_compress_minsz,
stats_size;
void *buf_data;
boolean_t full;
l2arc_write_callback_t *cb;
Expand All @@ -5739,7 +5739,7 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz,
*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;
Expand Down Expand Up @@ -5776,6 +5776,7 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz,
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);
Expand Down Expand Up @@ -5804,7 +5805,15 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz,
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;
Expand Down Expand Up @@ -5847,7 +5856,6 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz,
hdr->b_l2hdr.b_hits = 0;
hdr->b_l1hdr.b_tmp_cdata = hdr->b_l1hdr.b_buf->b_data;

buf_sz = hdr->b_size;
hdr->b_flags |= ARC_FLAG_HAS_L2HDR;

mutex_enter(&dev->l2ad_mtx);
Expand All @@ -5864,6 +5872,7 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz,
mutex_exit(hash_lock);

write_sz += buf_sz;
write_asize += buf_a_sz;
}

multilist_sublist_unlock(mls);
Expand All @@ -5882,6 +5891,19 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz,

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.
*/
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
Expand Down Expand Up @@ -5928,7 +5950,7 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz,

/* 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,
Expand All @@ -5939,13 +5961,14 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz,
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;
}
}

Expand All @@ -5955,8 +5978,8 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t 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.
Expand Down