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Reset l2ad_hand and l2ad_first in l2arc_evict

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Increasing l2arc_write_size or l2arc_write_boost can result in
l2arc_write_buffers() not having enough space to perform its writes and
panic zio_write_phys().

Instead of resetting l2ad_hand to l2ad_start at the end of
l2arc_write_buffers() and not taking into account a possible
user-mediated increase of l2arc_write_max, we do this in l2arc_evict(),
right after l2arc_write_size() has run. If there is not enough space to
evict (ie we will exceed l2ad_end) we evict to the end of the device,
reset l2ad_hand to l2ad_start, set l2ad_first to 0 and iterate
l2arc_evict(). We avoid infinite iteration of l2arc_evict() by making
sure in l2arc_write_size() that l2ad_start + size does not exceed
l2ad_end.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: George Amanakis <gamanakis@gmail.com>
Closes #10154
This commit is contained in:
George Amanakis
2020-03-31 13:46:48 -04:00
committed by GitHub
parent c96a32e1a3
commit 37c22948e5
6 changed files with 181 additions and 27 deletions
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module/zfs/arc.c
+52 -25
View File
@@ -7467,9 +7467,9 @@ l2arc_write_eligible(uint64_t spa_guid, arc_buf_hdr_t *hdr)
}
static uint64_t
l2arc_write_size(void)
l2arc_write_size(l2arc_dev_t *dev)
{
uint64_t size;
uint64_t size, dev_size;
/*
* Make sure our globals have meaningful values in case the user
@@ -7486,6 +7486,23 @@ l2arc_write_size(void)
if (arc_warm == B_FALSE)
size += l2arc_write_boost;
/*
* Make sure the write size does not exceed the size of the cache
* device. This is important in l2arc_evict(), otherwise infinite
* iteration can occur.
*/
dev_size = dev->l2ad_end - dev->l2ad_start;
if (size >= dev_size) {
cmn_err(CE_NOTE, "l2arc_write_max or l2arc_write_boost "
"exceeds the size of the cache device (guid %llu), "
"resetting them to the default (%d)",
dev->l2ad_vdev->vdev_guid, L2ARC_WRITE_SIZE);
size = l2arc_write_max = l2arc_write_boost = L2ARC_WRITE_SIZE;
if (arc_warm == B_FALSE)
size += l2arc_write_boost;
}
return (size);
}
@@ -8008,22 +8025,22 @@ l2arc_evict(l2arc_dev_t *dev, uint64_t distance, boolean_t all)
arc_buf_hdr_t *hdr, *hdr_prev;
kmutex_t *hash_lock;
uint64_t taddr;
boolean_t rerun;
buflist = &dev->l2ad_buflist;
if (!all && dev->l2ad_first) {
top:
rerun = B_FALSE;
if (dev->l2ad_hand >= (dev->l2ad_end - distance)) {
/*
* This is the first sweep through the device. There is
* nothing to evict.
*/
return;
}
if (dev->l2ad_hand >= (dev->l2ad_end - (2 * distance))) {
/*
* When nearing the end of the device, evict to the end
* before the device write hand jumps to the start.
* When there is no space to accomodate upcoming writes,
* evict to the end. Then bump the write hand to the start
* and iterate. This iteration does not happen indefinitely
* as we make sure in l2arc_write_size() that when l2ad_hand
* is reset, the write size does not exceed the end of the
* device.
*/
rerun = B_TRUE;
taddr = dev->l2ad_end;
} else {
taddr = dev->l2ad_hand + distance;
@@ -8031,7 +8048,15 @@ l2arc_evict(l2arc_dev_t *dev, uint64_t distance, boolean_t all)
DTRACE_PROBE4(l2arc__evict, l2arc_dev_t *, dev, list_t *, buflist,
uint64_t, taddr, boolean_t, all);
top:
if (!all && dev->l2ad_first) {
/*
* This is the first sweep through the device. There is
* nothing to evict.
*/
goto out;
}
retry:
mutex_enter(&dev->l2ad_mtx);
for (hdr = list_tail(buflist); hdr; hdr = hdr_prev) {
hdr_prev = list_prev(buflist, hdr);
@@ -8052,7 +8077,7 @@ top:
mutex_exit(&dev->l2ad_mtx);
mutex_enter(hash_lock);
mutex_exit(hash_lock);
goto top;
goto retry;
}
/*
@@ -8101,6 +8126,17 @@ top:
mutex_exit(hash_lock);
}
mutex_exit(&dev->l2ad_mtx);
out:
if (rerun) {
/*
* Bump device hand to the device start if it is approaching the
* end. l2arc_evict() has already evicted ahead for this case.
*/
dev->l2ad_hand = dev->l2ad_start;
dev->l2ad_first = B_FALSE;
goto top;
}
}
/*
@@ -8448,15 +8484,6 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz)
ARCSTAT_INCR(arcstat_l2_lsize, write_lsize);
ARCSTAT_INCR(arcstat_l2_psize, write_psize);
/*
* Bump device hand to the device start if it is approaching the end.
* l2arc_evict() will already have evicted ahead for this case.
*/
if (dev->l2ad_hand >= (dev->l2ad_end - target_sz)) {
dev->l2ad_hand = dev->l2ad_start;
dev->l2ad_first = B_FALSE;
}
dev->l2ad_writing = B_TRUE;
(void) zio_wait(pio);
dev->l2ad_writing = B_FALSE;
@@ -8539,7 +8566,7 @@ l2arc_feed_thread(void *unused)
ARCSTAT_BUMP(arcstat_l2_feeds);
size = l2arc_write_size();
size = l2arc_write_size(dev);
/*
* Evict L2ARC buffers that will be overwritten.