directory listing hangs in "ufs" state

[Andrey Zonov]

On 14.12.2011 22:53, Alan Cox wrote:
> On Wed, Dec 14, 2011 at 12:22 PM, Jeremy Chadwick
> <freebsd at jdc.parodius.com <mailto:freebsd at jdc.parodius.com>> wrote:
>
>     On Wed, Dec 14, 2011 at 10:11:47PM +0400, Andrey Zonov wrote:
>      > Hi Jeremy,
>      >
>      > This is not hardware problem, I've already checked that. I also ran
>      > fsck today and got no errors.
>      >
>      > After some more exploration of how mongodb works, I found that then
>      > listing hangs, one of mongodb thread is in "biowr" state for a long
>      > time. It periodically calls msync(MS_SYNC) accordingly to ktrace
>      > out.
>      >
>      > If I'll remove msync() calls from mongodb, how often data will be
>      > sync by OS?
>      >
>      > --
>      > Andrey Zonov
>      >
>      > On 14.12.2011 2:15, Jeremy Chadwick wrote:
>      > >On Wed, Dec 14, 2011 at 01:11:19AM +0400, Andrey Zonov wrote:
>      > >>
>      > >>Have you any ideas what is going on? or how to catch the problem?
>      > >
>      > >Assuming this isn't a file on the root filesystem, try booting the
>      > >machine in single-user mode and using "fsck -f" on the filesystem in
>      > >question.
>      > >
>      > >Can you verify there's no problems with the disk this file lives
>     on as
>      > >well (smartctl -a /dev/disk)?  I'm doubting this is the problem, but
>      > >thought I'd mention it.
>
>     I have no real answer, I'm sorry.  msync(2) indicates it's effectively
>     deprecated (see BUGS).  It looks like this is effectively a mmap-version
>     of fsync(2).
>
>
> Yikes, I just looked at this man page.  I'm afraid that the text in the
> BUGS section is highly misleading.  The MS_INVALIDATE option should be
> obsolete for the reason given there.  Under a strict reading of the
> applicable standard, FreeBSD could implement this option as a NOP.
> However, we treat it something like madvise(MADV_DONTNEED|FREE).  In
> contrast, MS_SYNC is definitely not obsolete.
>
> Alan
>
> P.S. If someone wants to take a crack at fixing this man page, contact
> me off list.
>

Please don't remove support for MS_INVALIDATE, this is only one way to 
purge disk cache. MADV_DONTNEED does nothing here in my experience.

-- 
Andrey Zonov