Bug 55523 – severe performance degradation when using samba's btrfs VFS object

Bug 55523 - severe performance degradation when using samba's btrfs VFS object


Summary:	severe performance degradation when using samba's btrfs VFS object

Status:	NEW

Product:	UCS
Classification:	Unclassified
Component:	Samba
Version:	UCS 5.0
Hardware:	amd64 Linux

Importance:	P5 normal (vote)
Target Milestone:	---
Assigned To:	Samba maintainers
QA Contact:	Samba maintainers

URL:
Keywords:

Depends on:
Blocks:
	Show dependency tree / graph

Reported:	2022-12-29 11:22 CET by Lionel Élie Mamane
Modified:	2022-12-29 11:36 CET (History)
CC List:	0 users

See Also:	https://bugzilla.samba.org/show_bug.cgi?id=15004
What kind of report is it?:	Bug Report
What type of bug is this?:	4: Minor Usability: Impairs usability in secondary scenarios
Who will be affected by this bug?:	3: Will affect average number of installed domains
How will those affected feel about the bug?:	2: A Pain – users won’t like this once they notice it
User Pain:	0.137
Enterprise Customer affected?:
School Customer affected?:
ISV affected?:
Waiting Support:
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Ticket number:
Bug group (optional):	UCS Performance, Workaround is available
Max CVSS v3 score:

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Description Lionel Élie Mamane 2022-12-29 11:22:58 CET

Enabling samba's "btrfs" VFS object on a share that is a btrfs mount (specifically, a subvolume, not sure if that makes a difference), performance of access from a Windows 10 client drops very very dramatically; e.g. right click on a file then "properties" takes tens of seconds.

The /var/log/samba/log.smbd log is filled with many many copies of messages like
  ../../source3/modules/vfs_btrfs.c:503(btrfs_fget_compression)
  btrfs_fget_compression: /proc open of /proc/self/fd/47 failed: Interrupted system call

and

  ../../source3/modules/vfs_btrfs.c:503(btrfs_fget_compression)
  btrfs_fget_compression: /proc open of /proc/self/fd/40 failed: Permission denied

According to https://bugzilla.samba.org/show_bug.cgi?id=15004 this is mostly bogus, and upstream samba has silenced that message (except in debug mode).

I think it would be worth to test whether the performance drop is "only" due to the logging overhead, and in this case to backport the trivial little upstream patch.

Comment 1 Lionel Élie Mamane 2022-12-29 11:30:05 CET

I wasn't sure whether you would consider this a "key scenario" or a "secondary scenario", so I took a guess. Feel free to correct.

Comment 2 Lionel Élie Mamane 2022-12-29 11:36:44 CET

UCS version 5.0-2
samba and samba-vfs-modules package version 2:4.16.2-1A~5.0.0.202211091951
linux-image-4.19.0-22-amd64 version 4.19.260-1
btrfs-progs    4.20.1-2

To be complete (but my guess is it does not matter for this issue), some shares are also under snapper management for automated snapshot management and have the samba snapper VFS module enabled. Low number of snapshots (less than 5 per subvolume), so the btrfs performance degradation that comes with a lot of snapshots should not be a factor.

snapper        0.8.2-1