Date: Fri, 15 Mar 2019 10:25:13 -0600 From: Alan Somers <asomers@freebsd.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: VOP_INACTIVE(9): reclaiming space for open but deleted files? Message-ID: <CAOtMX2gQLcPVD3-m94ZC51JTmqbhBft35CyRQh=9d2h1U9Tz9g@mail.gmail.com> In-Reply-To: <20190315151920.GC96870@kib.kiev.ua> References: <CAOtMX2iz%2BN6Esk2yzoeo-5_WxH2aF4LvvtumTWmGWdYiXZtZtA@mail.gmail.com> <20190315151920.GC96870@kib.kiev.ua>
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On Fri, Mar 15, 2019 at 9:19 AM Konstantin Belousov <kostikbel@gmail.com> wrote: > > On Fri, Mar 15, 2019 at 08:44:57AM -0600, Alan Somers wrote: > > VOP_INACTIVE(9) says that the vop can "be used to reclaim space for > > ‘open but deleted’ files". What does that mean? How can you reclaim > > space for open files? I assume it's just a mistake, but I want to > > check before I fix the man page. SVN archaeology shows that the line > > has been present since a mass import of man pages in 1997. > > VOP_INACTIVE() call means that the last use count for the vnode is > dereferenced. This can only happen when there is no more open files > using the vnode. > > Now consider what happens when you open file, then unlink it while > keeping the file opened. Filesystems usually mark such files with > VV_NOSYNC v_vflag, but there are typically other means to determine that > there is no name for the inode, like UFS i_nlink. On the last close > VOP_INACTIVE() is called (this is not guaranteed but you need to race to > not get the call). Then, if the vnode is not reclaimed, it is put on the > free list and the allocated blocks and other resources linger until the > vnode is reclaim (reclaim absolutely must free space for inodes which > cannot be reached). If inactive() frees the resources, the temporal > leak is avoided. > > As example look at UFS_INACTIVE(). If it detects file with effective link > count of zero, it resets i_mode and calls ffs_vfree() to free inode. Then > the vnode is reclaimed. Ok, so the man page is talking files which were formerly open but deleted, but are no longer open. I find the wording confusing. It seems to refer to files that are still open but deleted. -Alan
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