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Add a VM flag to prevent reclaim on a failed contig allocation
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Authored by rstone on Jan 29 2021, 9:17 PM.

Details

Summary

If a M_WAITOK contig alloc fails, the VM subsystem will try to
reclaim contiguous memory twice before actually failing the
request. On a system with 64GB of RAM I've observed this take
400-500ms before it finally gives up, and I believe that this
will only be worse on systems with even more memory.

In certain contexts this delay is extremely harmful, so add a flag
that will skip reclaim for allocation requests to allow those
paths to opt-out of doing an expensive reclaim.

Sponsored by: Dell Inc

Diff Detail

Repository
R10 FreeBSD src repository
Lint
Automatic diff as part of commit; lint not applicable.
Unit
Automatic diff as part of commit; unit tests not applicable.

Event Timeline

sys/sys/malloc.h
55

I think it is time to use 8 digits for M_ constants. Or use the flags from low byte, they are available I believe.

sys/vm/vm_page.h
551

Doesn't the value conflict with VM_ALLOC_COUNT() ?

sys/vm/vm_page.h
551

Oh jeez, I didn't even notice. Should I take 0x04 as bit 2 is supposed to be free or do we need to do something else here?

sys/vm/vm_page.h
551

I would take 0x80 or 0x800.

Fix overflap between new flag and count field

Change the value of M_NORECLAIM to avoid the style issue

This revision is now accepted and ready to land.Feb 1 2021, 8:15 PM