Date: Fri, 4 Jan 2002 17:28:33 -0600
From: Alfred Perlstein <bright@mu.org>
To: dillon@freebsd.org
Cc: fs@freebsd.org
Subject: open("", O_DIRECT) broken.
Message-ID: <20020104172833.R82406@elvis.mu.org>
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Open passed the O_DIRECT flag seems broken, instead of doing the
right thing which would be just to penalize buffers not in the
cache, what it does (at least from casual observation in ufs_readwrite)
is mark _all_ buffers read via a O_DIRECT file as wanting to be
discarded, this is bogus as you may read via an O_DIRECT method the
entire file and invalidate the cache of another process accessing
the same file.
It would be much better to pass O_DIRECT down to bread{n} which
would only mark it as B_DIRECT if it's not found in the cache.
The idea is to not be distruptive to the cache, not to prematurely
toss away buffers that may be otherwise benifiting from heavy cache
utilization.
--
-Alfred Perlstein [alfred@freebsd.org]
'Instead of asking why a piece of software is using "1970s technology,"
start asking why software is ignoring 30 years of accumulated wisdom.'
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