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Bug #7606

dmu_objset_find_dp() takes a long time while importing pool

Added by Prakash Surya about 4 years ago. Updated about 4 years ago.

Status:
Closed
Priority:
Normal
Assignee:
Category:
zfs - Zettabyte File System
Start date:
2016-11-21
Due date:
% Done:

100%

Estimated time:
Difficulty:
Medium
Tags:
needs-triage
Gerrit CR:

Description

When importing a pool with a large number of filesystems within the same
parent filesystem, we see that dmu_objset_find_dp() takes a long time.
It is called from 3 places: spa_check_logs(), spa_ld_claim_log_blocks(),
and spa_load_verify().

There are several ways to improve performance here:

1. We don't really need to do spa_check_logs() or
spa_ld_claim_log_blocks() if the pool was closed cleanly.
2. spa_load_verify() uses dmu_objset_find_dp() to check that no
datasets have too long of names.
3. dmu_objset_find_dp() is slow because it's doing
zap_value_search() (which is O(N sibling datasets)) to determine
the name of each dsl_dir when it's opened. In this case we
actually know the name when we are opening it, so we can provide
it and avoid the lookup.

This change implements fix #3 from the above list; i.e. make
dmu_objset_find_dp() provide the name of the dataset so that we don't
have to search for it.

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