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Differential D45381

kern/dev/xen: Use the per-blkback-device uma(9) zone for the bio.
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Authored by seigo.tanimura_gmail.com on May 27 2024, 10:09 AM.
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royger

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olce
royger
Summary

The usage is essentially the same as the VM swap pager.

  • New Loader Tunable & Sysctl Entry
  • hw.xbd.xbb_reserved_new_bios The number of the bios reserved and preallocated per device. This is writable for hotplug.

Signed-off-by: Seigo Tanimura <seigo.tanimura@gmail.com>

Diff Detail

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rG FreeBSD src repository
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Build Status
Buildable 57934
Build 54822: arc lint + arc unit

Event Timeline

seigo.tanimura_gmail.com created this revision.May 27 2024, 10:09 AM
Herald added subscribers: ehem_freebsd_m5p.com, imp. · View Herald TranscriptMay 27 2024, 10:09 AM
seigo.tanimura_gmail.com requested review of this revision.May 27 2024, 10:09 AM
Harbormaster completed remote builds in B57934: Diff 139136.May 27 2024, 10:09 AM
seigo.tanimura_gmail.com added a parent revision: D45215: kern/geom: Make the struct bio allocation more robust to a heavy load..May 27 2024, 10:09 AM
seigo.tanimura_gmail.com mentioned this in D45215: kern/geom: Make the struct bio allocation more robust to a heavy load..
olce added a reviewer: olce.May 27 2024, 1:09 PM
olce mentioned this in D45379: kern/vm: Use the dedicated bio zone for the swap bio..May 27 2024, 1:11 PM
ehem_freebsd_m5p.com added a subscriber: royger.Jun 4 2024, 3:41 AM

The one to consider D45381 is @royger who handles the Xen interface for FreeBSD.

At first glance this looks plausible, though running on Xen might mean some decisions should be different.

royger added a reviewer: royger.Jun 4 2024, 9:24 AM
royger added a comment.Jun 4 2024, 9:46 AM

Some questions. I mostly miss where g_io_new_uz() and the new set of helpers are introduced, as I'm not finding them in main git branch yet?

Since this seems to be a performance improvement, do you have some figures on how much of a performance difference does this change make?

sys/dev/xen/blkback/blkback.c
75

Ideally includes should be sorted alphabetically if possible, so vm/uma.h should be at the top of the vm/ group.

765

static unsigned int, and the max amount of in-flight BIOs blkback can currently handle is set by XBB_MAX_REQUESTS.

2002

Does this change depend on some unmerged stuff? I'm not able to find g_new_bio_uz() on the current main branch, neither g_io_new_uz(). How does it behave when it gets passed NULL as argument.

2003

If the uma pool is allocated to account for the maximum amuont of possible in-flights BIOs, the bio == NULL is no longer possible, and hence a KASSERT should be added inside of the if expression block.

ehem_freebsd_m5p.com added a comment.Jun 4 2024, 11:07 PM

@royger under "Revision Contents" select the red tab "Stack (2 Open)". This is how Phabricator handles series and interrelated commits. The bits you were wondering about are there.

Revision Contents
Changeset List

PathSize
share/
man/
man4/
8 lines
sys/
dev/
xen/
blkback/
29 lines

Diff 139136

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share/man/man4/xen.4

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sys/dev/xen/blkback/blkback.c

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