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Improve ZFS objset sync parallelism

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As part of transaction group commit, dsl_pool_sync() sequentially calls
dsl_dataset_sync() for each dirty dataset, which subsequently calls
dmu_objset_sync().  dmu_objset_sync() in turn uses up to 75% of CPU
cores to run sync_dnodes_task() in taskq threads to sync the dirty
dnodes (files).

There are two problems:

1. Each ZVOL in a pool is a separate dataset/objset having a single
   dnode.  This means the objsets are synchronized serially, which
   leads to a bottleneck of ~330K blocks written per second per pool.

2. In the case of multiple dirty dnodes/files on a dataset/objset on a
   big system they will be sync'd in parallel taskq threads. However,
   it is inefficient to to use 75% of CPU cores of a big system to do
   that, because of (a) bottlenecks on a single write issue taskq, and
   (b) allocation throttling.  In addition, if not for the allocation
   throttling sorting write requests by bookmarks (logical address),
   writes for different files may reach space allocators interleaved,
   leading to unwanted fragmentation.

The solution to both problems is to always sync no more and (if
possible) no fewer dnodes at the same time than there are allocators
the pool.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Edmund Nadolski <edmund.nadolski@ixsystems.com>
Closes #15197
This commit is contained in:
ednadolski-ix
2023-11-06 11:38:42 -07:00
committed by GitHub
parent 0527774066
commit 3bd4df3841
18 changed files with 513 additions and 118 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/os/freebsd/spl/sys/taskq.h
+3
View File
@@ -42,6 +42,7 @@ extern "C" {
typedef struct taskq {
struct taskqueue *tq_queue;
int tq_nthreads;
} taskq_t;
typedef uintptr_t taskqid_t;
@@ -93,6 +94,8 @@ extern void taskq_dispatch_ent(taskq_t *, task_func_t, void *, uint_t,
taskq_ent_t *);
extern int taskq_empty_ent(taskq_ent_t *);
taskq_t *taskq_create(const char *, int, pri_t, int, int, uint_t);
taskq_t *taskq_create_synced(const char *, int, pri_t, int, int, uint_t,
kthread_t ***);
taskq_t *taskq_create_instance(const char *, int, int, pri_t, int, int, uint_t);
taskq_t *taskq_create_proc(const char *, int, pri_t, int, int,
struct proc *, uint_t);
include/os/linux/spl/sys/taskq.h
+2
View File
@@ -150,6 +150,8 @@ extern void taskq_dispatch_ent(taskq_t *, task_func_t, void *, uint_t,
extern int taskq_empty_ent(taskq_ent_t *);
extern void taskq_init_ent(taskq_ent_t *);
extern taskq_t *taskq_create(const char *, int, pri_t, int, int, uint_t);
extern taskq_t *taskq_create_synced(const char *, int, pri_t, int, int, uint_t,
kthread_t ***);
extern void taskq_destroy(taskq_t *);
extern void taskq_wait_id(taskq_t *, taskqid_t);
extern void taskq_wait_outstanding(taskq_t *, taskqid_t);