Date: Fri, 12 Oct 2001 16:30:01 -0700 (PDT) From: Matt Dillon <dillon@earth.backplane.com> To: Dag-Erling Smorgrav <des@ofug.org> Cc: cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Re: cvs commit: src/sys/vm vnode_pager.c Message-ID: <200110122330.f9CNU1u36917@earth.backplane.com> References: <200110121817.f9CIHYU38714@freefall.freebsd.org> <xzpelo8ii94.fsf@flood.ping.uio.no>
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:Matt Dillon <dillon@FreeBSD.org> writes:
:> Log:
:> Finally fix the VM bug where a file whos EOF occurs in the middle of a page
:> would sometimes prevent a dirty page from being cleaned, even when synced,
:> resulting in the dirty page being re-flushed to disk every 30-60 seconds or
:> so, forever.
:
:Does this explain why my development box (with FreeBSD, NetBSD and
:XFree86 repo mirrors and about three full FreeBSD source trees checked
:out) has a shitload of FFS nodes and spends 8% of its time running
:syncer, resulting in crappy interrupt latency? Or is that a different
:bug? If this is the one, I'm immensely grateful that you fixed it.
:
:DES
:--
:Dag-Erling Smorgrav - des@ofug.org
Possibly. Apply the patch and find out, I'd really like to know if it
makes a difference. An uncleanable page would prevent a vnode from
being reused and would result in higher syncer overhead. But there are
other possibilities as well.. for example, heavy use of MAP_NOSYNC
can result in higher syncer overheads (but would not result in higher
disk loads). Your description of the repo mirrors fits the scenario.
One other thing to note in regards to repo-mirrors... if files are
being accessed a lot, you may want to mount the partitions 'noatime'
or the constant scanning will result in higher syncer & disk overheads.
This can be demonstrated quite easily. In one xterm run 'systat -vm 1'
and begin observing the 'dirtybuf' statistic. In another xterm run
'ls -lR /' (on a local disk), and observe the dirtybuffer count go up...
and that's just for updating the atimes on the directories!
-Matt
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