This patch fixes a problem caused by applications that rapidly and

repeatedly truncate the same file. Each time the file is truncated,
a buffer is grabbed to store the indirect block numbers that need
to be freed. Those blocks cannot be freed until the inode claiming
them is written to disk. Thus, the number of buffers being held by
soft updates explodes and in extreme cases can run the kernel out
of buffers. The problem can be avoided by doing an fsync on the
file every debug.maxindirdep truncates (currently defaulted to 50).
The fsync causes the inode to be written so that the held buffers
can be freed. The check for excessive buffers is checked as part
of the existing hook for excessive dependencies (softdep_slowdown)
in the truncate code.

Reported by:	David Schultz <dschultz@uclink.Berkeley.EDU>
Sponsored by:   DARPA & NAI Labs.
MFC after:	3 weeks

0 files changed, 0 insertions, 0 deletions