Date: Tue, 26 Apr 2005 15:36:02 -0400 From: Brian Fundakowski Feldman <green@freebsd.org> To: Marc Olzheim <marcolz@stack.nl> Cc: freebsd-stable@freebsd.org Subject: Re: NFS client/buffer cache deadlock Message-ID: <20050426193602.GE5789@green.homeunix.org> In-Reply-To: <20050426164346.GA68763@stack.nl> References: <20050420142448.GH1157@green.homeunix.org> <20050420143842.GB77731@stack.nl> <16998.36437.809896.936800@khavrinen.csail.mit.edu> <20050420173859.GA99695@stack.nl> <20050426140701.GB5789@green.homeunix.org> <20050426151751.GB68038@stack.nl> <20050426155043.GC5789@green.homeunix.org> <20050426160609.GA68511@stack.nl> <20050426162549.GD5789@green.homeunix.org> <20050426164346.GA68763@stack.nl>
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On Tue, Apr 26, 2005 at 06:43:46PM +0200, Marc Olzheim wrote: > [changed cc: from standards@ back to stable@ again.] > > On Tue, Apr 26, 2005 at 12:25:49PM -0400, Brian Fundakowski Feldman wrote: > > You can assure that this happens in only two ways: > > > > 1. Make a complete copy of the data. This is what currently occurs: > > it gets stuffed into the buffer cache as the write happens. > > 2. Keep the data around synchronously -- by virtue of the write system > > call being used synchronously, the thread's VM context is around, > > and duplication need not occur. > > It seems as though FreeBSD 4.x either used 2) or does something wrong > indeed. Why would 2) be a problem on FreeBSD 5.x ? Can't the pages > written from be locked during the write, instead of copied internally ? I'm still guessing that for whatever reason your writes on the FreeBSD 4.x NFS client are not using NFSv3/transactions. The second method I just now implemented; it works fine except for being slower since all data is acknowledged synchronously. Are you using one writev() instead of many writes so you can atomically write a large sparse data structure? If so, you will probably just have to cope with the lower performance than for reasonably-sized writes. If not: why are you trying to write it atomically? Just use multiple normal-sized write() calls. > Btw. running the writev program with 20 * 100 MB on UFS on a 512MB > FreeBSD 6-CURRENT system practicly locks the filesystem down _and_ > causes all processes to be swapped out in favor of the buffer cache. > 'top' however, doesnt' show a rise in BUF usage. > > On FreeBSD 4.x, the system performance as usual during the writev to > UFS. That's certainly not very optimal. I don't know anything about it, sorry. -- Brian Fundakowski Feldman \'[ FreeBSD ]''''''''''\ <> green@FreeBSD.org \ The Power to Serve! \ Opinions expressed are my own. \,,,,,,,,,,,,,,,,,,,,,,\
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