Re: [PATCH 0/4] 2.6.21-rc7 NFS writes: fix a series of issues

Linus Torvalds
2007-04-18T05:17:27Z

On Tue, 17 Apr 2007, Florin Iucha wrote:
>
> Already did. Traces from vanilla kernel at
> http://iucha.net/nfs/21-rc7/big-copy

Well, there's a pdflush in io_schedule_timeout/congestion_wait, and
there's a nfsv4-scv in svc_recv/nfs_callback_sv, and a lot of processes
either just in schedule_timeout or similar "normal" waiting (pollwait
etc).

[ The call traces could be prettier, but sadly, even if you enable frame
pointers, the x86-64 kernel is too stupid to follow them. So you kind of
just have to ignore the noise) ]

The triggering process looks like it might be that "cp", it is in the
__wait_on_bit/sync_page/wait_on_page_bit/wait_on_page_writeback_range/
filemap_fdatawait.

Is this a trace from the "big copy" hang, or from a gnome splashscreen
hang? It *looks* like it's a big copy. Yes/no?

Anyway, looks like the cp did a "utimes()" system call, which triggers
"nfs_setattr(), which in turn triggers the filemap_fdatawait() and some
kind of endless wait. Nothing stands out from the traces, in other words.
Doesn't look like a locking thing, for example - we're not stuck on some
inode semaphore, we're literally waiting for the page to be written out.

Linus