[LU-5749] osd-zfs: object creation may serialize on lu_site::ls_purge_mutex

• Type: Improvement
• Resolution: Duplicate
• Priority: Minor
• Affects Version/s: Lustre 2.7.0
• Labels: RZ_LS zfs
• Assignee: Alex Zhuravlev
• Reporter: Isaac Huang (Inactive)

Description

LU-5331 introduced lu_site::ls_purge_mutex to serialize lu_site_purge(). But in osd-zfs, when every new object is created, lu_object_limit() is called which calls lu_site_purge() if the cache is too big.

Contention on the mutex can happen when multiple threads are creating objects and the cache is near the lu_cache_nr limit. In LU-5747 I saw stacks like:

 [<ffffffff8106306c>] try_to_wake_up+0x3c/0x3e0
 [<ffffffffa0f0e219>] ? echo_object_free+0x159/0x2f0 [obdecho]
 [<ffffffff81063465>] wake_up_process+0x15/0x20
 [<ffffffff8150f7e4>] __mutex_unlock_slowpath+0x44/0x60
 [<ffffffff8150f79b>] mutex_unlock+0x1b/0x20
 [<ffffffffa07a4907>] lu_site_purge+0x3f7/0x4e0 [obdclass]
 [<ffffffffa07a4e31>] lu_object_limit+0x71/0x80 [obdclass]
 [<ffffffffa07a4f93>] lu_object_find_try+0x153/0x2b0 [obdclass]

Which indicated contention on the mutex. So this may hurt object creation rates on osd-zfs. But I don't have any data to support it yet, due to LU-5747.

Issue Links

• is related to: LU-5331 qsd_handler.c:1139:qsd_op_adjust()) ASSERTION( qqi ) failed
• is related to: LU-7896 lu_object_limit() is called too frequently