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Disable direct reclaim for z_wr_* threads

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The direct reclaim path in the z_wr_* threads must be disabled
to ensure forward progress is always maintained for txg processing.
This ensures that a txg will never get stuck waiting on itself
because it entered the following memory reclaim callpath.

  ->prune_icache()->dispose_list()->zpl_clear_inode()->zfs_inactive()
  ->dmu_tx_assign()->dmu_tx_wait()->tgx_wait_open()

It would be preferable to target this exact code path but the
kernel offers no way to do this without custom patches.  To avoid
this we are forced to disable all reclaim for these threads.  It
should not be necessary to do this for other other z_* threads
because they will not hold a txg open.

Closes #232
This commit is contained in:
Brian Behlendorf
2011-05-06 15:12:15 -07:00
parent 3117dd0b90
commit 21ade34764
2 changed files with 7 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files
module/zfs/spa.c
+6 -3
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@@ -614,9 +614,8 @@ spa_get_errlists(spa_t *spa, avl_tree_t *last, avl_tree_t *scrub)
static taskq_t *
spa_taskq_create(spa_t *spa, const char *name, enum zti_modes mode,
uint_t value)
uint_t value, uint_t flags)
{
uint_t flags = TASKQ_PREPOPULATE;
boolean_t batch = B_FALSE;
switch (mode) {
@@ -666,13 +665,17 @@ spa_create_zio_taskqs(spa_t *spa)
const zio_taskq_info_t *ztip = &zio_taskqs[t][q];
enum zti_modes mode = ztip->zti_mode;
uint_t value = ztip->zti_value;
uint_t flags = TASKQ_PREPOPULATE;
char name[32];
if (t == ZIO_TYPE_WRITE)
flags |= TASKQ_NORECLAIM;
(void) snprintf(name, sizeof (name),
"%s_%s", zio_type_name[t], zio_taskq_types[q]);
spa->spa_zio_taskq[t][q] =
spa_taskq_create(spa, name, mode, value);
spa_taskq_create(spa, name, mode, value, flags);
}
}
}