Date: Tue, 15 Oct 2002 17:19:25 -0700 (PDT) From: Kirk McKusick <mckusick@FreeBSD.org> To: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: cvs commit: src/sys/ufs/ffs ffs_snapshot.c Message-ID: <200210160019.g9G0JSxq085250@repoman.freebsd.org>
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mckusick 2002/10/15 17:19:25 PDT
Modified files:
sys/ufs/ffs ffs_snapshot.c
Log:
Change locking so that all snapshots on a particular filesystem share
a common lock. This change avoids a deadlock between snapshots when
separate requests cause them to deadlock checking each other for a
need to copy blocks that are close enough together that they fall
into the same indirect block. Although I had anticipated a slowdown
from contention for the single lock, my filesystem benchmarks show
no measurable change in throughput on a uniprocessor system with
three active snapshots. I conjecture that this result is because
every copy-on-write fault must check all the active snapshots, so
the process was inherently serial already. This change removes the
last of the deadlocks of which I am aware in snapshots.
Sponsored by: DARPA & NAI Labs.
Revision Changes Path
1.45 +91 -42 src/sys/ufs/ffs/ffs_snapshot.c
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