failure to sync vnodes/buffers

hi there,

yesterday during a regular reboot my system was unable to sync vnodes and
buffers. vnodes went down to 1, but then it kept repeating 1 until a timeout
was hit. the output of the buffer syncs was running so fast i could hardly make
out any numbers at all (but i took a picture, if anyone's interested in it).

it seems i'm having the same issue as described in PR #132397.

this happens quite regularly actually, but only after my system has been
running for a few days and heavy I/O to the disk occured during that period of
time.

any advice? running HEAD (r212665; amd64).

cheers.
alex

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a13x