From owner-freebsd-fs@FreeBSD.ORG Thu Jun 14 11:32:42 2012 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (unknown [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E03D91065672 for ; Thu, 14 Jun 2012 11:32:42 +0000 (UTC) (envelope-from rmacklem@uoguelph.ca) Received: from esa-scalar.mail.uoguelph.ca (esa-scalar.mail.uoguelph.ca [66.199.40.18]) by mx1.freebsd.org (Postfix) with ESMTP id 7CAC18FC08 for ; Thu, 14 Jun 2012 11:32:42 +0000 (UTC) Received: from zcs3.mail.uoguelph.ca (new.mail.uoguelph.ca [131.104.93.37]) by esa-scalar.mail.uoguelph.ca (8.14.1/8.14.1) with ESMTP id q5EBWa2B019861; Thu, 14 Jun 2012 07:32:36 -0400 Received: from zcs3.mail.uoguelph.ca (localhost.localdomain [127.0.0.1]) by zcs3.mail.uoguelph.ca (Postfix) with ESMTP id 3BF66B406E; Thu, 14 Jun 2012 07:32:36 -0400 (EDT) Date: Thu, 14 Jun 2012 07:32:36 -0400 (EDT) From: Rick Macklem To: Pavlo Message-ID: <893489718.1762311.1339673556220.JavaMail.root@erie.cs.uoguelph.ca> In-Reply-To: <91943.1339669820.1305529125424791552@ffe15.ukr.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [172.17.91.201] X-Mailer: Zimbra 6.0.10_GA_2692 (ZimbraWebClient - FF3.0 (Win)/6.0.10_GA_2692) Cc: freebsd-fs@freebsd.org Subject: Re: mmap() incoherency on hi I/O load (FS is zfs) X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 14 Jun 2012 11:32:43 -0000 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"