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Remove b_pabd/b_rabd allocation from arc_hdr_alloc()

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When a header is allocated for full overwrite it is a waste of time
to allocate b_pabd/b_rabd for it, since arc_write() will free them
without ever being touched.  If it is a read or a partial overwrite
then arc_read() and arc_hdr_decrypt() allocate them explicitly.

Reduced memory allocation in user threads also reduces ARC eviction
throttling there, proportionally increasing it in ZIO threads, that
is not good.  To minimize or even avoid it introduce ARC allocation
reserve, allowing certain arc_get_data_abd() callers to allocate a
bit longer in situations where user threads will already throttle.

Reviewed-by: George Wilson <gwilson@delphix.com>
Reviewed-by: Mark Maybee <mark.maybee@delphix.com>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored-By: iXsystems, Inc.
Closes #12398
This commit is contained in:
Alexander Motin
2021-08-17 12:15:54 -04:00
committed by GitHub
parent 72f0521aba
commit 6b88b4b501
4 changed files with 68 additions and 51 deletions
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include/sys/arc_impl.h
+1 -1
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@@ -988,7 +988,7 @@ extern unsigned long zfs_arc_max;
extern void arc_reduce_target_size(int64_t to_free);
extern boolean_t arc_reclaim_needed(void);
extern void arc_kmem_reap_soon(void);
extern void arc_wait_for_eviction(uint64_t);
extern void arc_wait_for_eviction(uint64_t, boolean_t);
extern void arc_lowmem_init(void);
extern void arc_lowmem_fini(void);