Date: Thu, 14 Jun 2012 14:50:45 +0300 From: "Pavlo" <devgs@ukr.net> To: "Rick Macklem" <rmacklem@uoguelph.ca> Cc: freebsd-fs@freebsd.org Subject: Re: mmap() incoherency on hi I/O load (FS is zfs) Message-ID: <14119.1339674645.325291171772956672@ffe5.ukr.net> In-Reply-To: <893489718.1762311.1339673556220.JavaMail.root@erie.cs.uoguelph.ca> References: <893489718.1762311.1339673556220.JavaMail.root@erie.cs.uoguelph.ca>
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> Pavlo wrote: > There's a case when some parts of files that are mapped and then > modified getting corrupted. By corrupted I mean some data is ok (one > that > was written using write()/pwrite()) but some looks like it never > existed. > Like it was some time in buffers, when several processes > simultaneously > (of course access was synchronised) used shared pages and reported > it's > existence. But after time pass they (processes) screamed that it is > now > lost. Only part of data written with pwrite() was there. Everything > that > was written via mmap() is zero. > > So as I said it occurs on hi I/O busyness. When in background 4+ > processes do indexing of huge ammount of data. Also I want to note, it > never occurred in the life of our project while we used mmap() under > same I/O stress conditions when mapping was done for a whole file of > just > a part(header) starting from a beginning of a file. First time we used > mapping of individual pages, just to save RAM, and this popped up. > > Solution for this problem is msync() before any munmap(). But man > says: > > The msync() system call is usually not needed since BSD implements a > coherent file system buffer cache. However, it may be used to > associate > dirty VM pages with file system buffers and thus cause them to be > flushed > to physical media sooner rather than later. > > Any thoughts? Thanks. > With a recent kernel from head, I am seeing dirty mmap'd pages being written quite late for the NFSv4 client. Even after the NFS client VOP_RECLAIM() has been called, it seems. I didn't observe this behaviour in a kernel from head in March. (I don't know enough about the vm/mmap area to know if this is correct behaviour or not?) I thought I'd mention this, since you didn't say how recent a kernel you were running and thought it might be caused by the same change? Sorry I can't help more, rick > _______________________________________________ > freebsd-fs@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-fs>; To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org" > Thanks for reply, Rick! Yes, we have pretty old kernel: # uname -a FreeBSD mpop-zebra-k1.ukr.net 8.2-STABLE FreeBSD 8.2-STABLE #9: Wed Jan 25 11:28:55 EET 2012 I just posted my observation here to point out possible problem that could still exist.
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