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L2ARC: Relax locking during write

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Previous code held ARC state sublist lock throughout all L2ARC
write process, which included number of allocations and even ZIO
issues.  Being blocked in any of those places the code could also
block ARC eviction, that could cause OOM activation or even dead-
lock if system is low on memory or one is too fragmented.

Fix it by dropping the lock as soon as we see a block eligible
for L2ARC writing and pick it up later using earlier inserted
marker.  While there, also reduce scope of hash lock, moving
ZIO allocation and other operations not requiring header access
out of it.  All operations requiring header access move under
hash lock, since L2_WRITING flag does not prevent header eviction
only transition to arc_l2c_only state with L1 header.

To be able to manipulate sublist lock and marker as needed add few
more multilist functions and modify one.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Closes #16040
This commit is contained in:
Alexander Motin
2024-04-09 19:23:19 -04:00
committed by GitHub
parent 9e63631dea
commit 997f85b4d3
6 changed files with 136 additions and 104 deletions
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include/sys/multilist.h
+4 -1
View File
@@ -82,12 +82,15 @@ int multilist_is_empty(multilist_t *);
unsigned int multilist_get_num_sublists(multilist_t *);
unsigned int multilist_get_random_index(multilist_t *);
multilist_sublist_t *multilist_sublist_lock(multilist_t *, unsigned int);
void multilist_sublist_lock(multilist_sublist_t *);
multilist_sublist_t *multilist_sublist_lock_idx(multilist_t *, unsigned int);
multilist_sublist_t *multilist_sublist_lock_obj(multilist_t *, void *);
void multilist_sublist_unlock(multilist_sublist_t *);
void multilist_sublist_insert_head(multilist_sublist_t *, void *);
void multilist_sublist_insert_tail(multilist_sublist_t *, void *);
void multilist_sublist_insert_after(multilist_sublist_t *, void *, void *);
void multilist_sublist_insert_before(multilist_sublist_t *, void *, void *);
void multilist_sublist_move_forward(multilist_sublist_t *mls, void *obj);
void multilist_sublist_remove(multilist_sublist_t *, void *);
int multilist_sublist_is_empty(multilist_sublist_t *);