[LU-3338] IOC_MDC_GETFILESTRIPE can abuse vmalloc()

• Type: Bug
• Resolution: Fixed
• Priority: Major
• Fix Version/s: Lustre 2.6.0
• Affects Version/s: Lustre 2.4.0
• Labels: patch
• Environment: x86_64 client

Epic/Theme

Performance

• Story Points: 1
• Severity: 3

Epic

client

• Assignee: Lai Siyao
• Reporter: Brian Behlendorf

Description

We've observed that when using Robinhood to scan the Sequoia filesystem the Lustre 2.3.65 (and earlier) clients will thrash in vmalloc(). The issue is caused by Robinhood repeatedly calling IOC_MDC_GETFILESTRIPE to get the striping information for the files which it is scanning.

Normally this wouldn't be an issue but because Sequoia's filesystem has a large number of OSTs (768). And because we always allocate space in the reply buffer for the maximum numbers of OSTs. All of the reply buffers end up getting vmalloc()'ed instead of kmalloc()'ed by OBD_ALLOC_LARGE().

It's worth noting that we see this behavior even though we're running with the fix for the recent kernel vmalloc() regression. Going forward we should keep this in mind and never ever use vmalloc() if we can at all avoid it. It's not just slow, it's downright dangerous to use in any concurrent context.

I'll push a fix for this issue shortly for review.

Issue Links

• is related to: LU-4811 Interop 2.5<->2.6 failure on test suite sanity test_24u: error on ioctl 0x4008669a, no data availiable
• is related to: LU-5549 cl_default_mds_easize not refreshed