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OpenZFS 9337 - zfs get all is slow due to uncached metadata

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This project's goal is to make read-heavy channel programs and zfs(1m)
administrative commands faster by caching all the metadata that they will
need in the dbuf layer. This will prevent the data from being evicted, so
that any future call to i.e. zfs get all won't have to go to disk (very
much). There are two parts:

The dbuf_metadata_cache. We identify what to put into the cache based on
the object type of each dbuf.  Caching objset properties os
{version,normalization,utf8only,casesensitivity} in the objset_t. The reason
these needed to be cached is that although they are queried frequently,
they aren't stored in a dbuf type which we can easily recognize and cache in
the dbuf layer; instead, we have to explicitly store them. There's already
existing infrastructure for maintaining cached properties in the objset
setup code, so I simply used that.

Performance Testing:

 - Disabled kmem_flags
 - Tuned dbuf_cache_max_bytes very low (128K)
 - Tuned zfs_arc_max very low (64M)

Created test pool with 400 filesystems, and 100 snapshots per filesystem.
Later on in testing, added 600 more filesystems (with no snapshots) to make
sure scaling didn't look different between snapshots and filesystems.

Results:

    | Test                   | Time (trunk / diff) | I/Os (trunk / diff) |
    +------------------------+---------------------+---------------------+
    | zpool import           |     0:05 / 0:06     |    12.9k / 12.9k    |
    | zfs get all (uncached) |     1:36 / 0:53     |    16.7k / 5.7k     |
    | zfs get all (cached)   |     1:36 / 0:51     |    16.0k / 6.0k     |

Authored by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Thomas Caputi <tcaputi@datto.com>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Approved by: Richard Lowe <richlowe@richlowe.net>
Ported-by: Alek Pinchuk <apinchuk@datto.com>
Signed-off-by: Alek Pinchuk <apinchuk@datto.com>

OpenZFS-issue: https://illumos.org/issues/9337
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/7dec52f
Closes #7668
This commit is contained in:
Matthew Ahrens
2018-07-10 13:49:50 -04:00
committed by Brian Behlendorf
parent e4e94ca315
commit 2e5dc449c1
17 changed files with 405 additions and 164 deletions
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include/sys/dmu.h
+6 -1
View File
@@ -107,7 +107,8 @@ typedef enum dmu_object_byteswap {
/*
* Defines a uint8_t object type. Object types specify if the data
* in the object is metadata (boolean) and how to byteswap the data
* (dmu_object_byteswap_t).
* (dmu_object_byteswap_t). All of the types created by this method
* are cached in the dbuf metadata cache.
*/
#define DMU_OT(byteswap, metadata, encrypted) \
(DMU_OT_NEWTYPE | \
@@ -119,6 +120,9 @@ typedef enum dmu_object_byteswap {
((ot) & DMU_OT_BYTESWAP_MASK) < DMU_BSWAP_NUMFUNCS : \
(ot) < DMU_OT_NUMTYPES)
#define DMU_OT_IS_METADATA_CACHED(ot) (((ot) & DMU_OT_NEWTYPE) ? \
B_TRUE : dmu_ot[(ot)].ot_dbuf_metadata_cache)
/*
* MDB doesn't have dmu_ot; it defines these macros itself.
*/
@@ -883,6 +887,7 @@ typedef void (*const arc_byteswap_func_t)(void *buf, size_t size);
typedef struct dmu_object_type_info {
dmu_object_byteswap_t ot_byteswap;
boolean_t ot_metadata;
boolean_t ot_dbuf_metadata_cache;
boolean_t ot_encrypt;
char *ot_name;
} dmu_object_type_info_t;