Date: Fri, 25 Jun 1999 21:07:51 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Greg Lehey <grog@lemis.com> Cc: Kirk McKusick <mckusick@FreeBSD.ORG>, cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Re: cvs commit: src/sys/sys buf.h lock.h src/sys/kern kern_lock.c kern_physio.c kern_shutdown.c subr_dkbad.c vfs_aio.c vfs_bio.c vfs_cluster.c vfs_subr.c src/sys/miscfs/devfs devfs_vnops.c src/sys/miscfs/specfs spec_vnops.c src/sys/msdosfs msdosfs_vnops.c ... Message-ID: <199906260407.VAA97427@apollo.backplane.com> References: <199906260247.TAA84326@freefall.freebsd.org> <19990626122708.B427@freebie.lemis.com>
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:> semantics. That is, all buffer locking is done with LK_EXCLUSIVE
:> requests. Changes to take advantage of LK_SHARED and LK_RECURSIVE will
:> be done in future commits.
:
:Is this worth a "heads up"? It'll change the way a lot of things have
:been done.
:
:Greg
:--
Yes, definitely!
The change Kirk is making has several immediate effects. First, it is
a necessary precursor to his snapshot code for softupdates. Secondly,
it will help us address performance issues with the current aggressive
write-behind code in the filesystem (e.g. filesystem doing bawrite()s
rather then bdwrites()s in certain situations). Changing the bawrite()s
to bdwrite()s is not easy to do because it stresses the buffer cache in
weird ways at the moment. The change will allow us to fix performance
snags with bawrite()s.
Third, the effect allows general sharing of buffers in the buffer cache
which is not only the basis for the above two items, but will also probably
become the basis for future performance enhancements.
Unfortunately, this also has the effect of digging deep into the VFS
system. But it's a necessary change.
-Matt
Matthew Dillon
<dillon@backplane.com>
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