On 22/11/06, David Chinner <dgc@xxxxxxx> wrote:
On Tue, Nov 21, 2006 at 11:02:23PM +0100, Jesper Juhl wrote: > On 21/11/06, David Chatterton <chatz@xxxxxxxxxxxxxxxxx> wrote:
...
> >Audits have been done in the past and will again be done in the future to > >try to > >identify areas where XFS could use less stack space by reducing/avoid large > >local variables. Reducing the code path is far more difficult. > > > I realize that fixing the problem may be difficult. I just wanted to > make sure that people were informed that there is an actual problem > and provide as much info as possible so that perhaps in the future it > can be fixed... :) I've got one that prevents gcc from inlining single use functions in XFS that I need to finish off, and that results in some significant stack usage reductions in some XFS functions.
That sounds good. I'll be keeping an eye out for that one :)
However, XFS is only one part of the picture - when you put NFS on top, DM+md then scsi/FC below and then you nest a soft irq that might go 20 functions deep as well - then 4k stacks simply aren't big enough.
True, there are a lot of players involved here, although XFS seems (to me) to be the biggest one.
> I'm reading through the XFS code myself at the moment and I'll be sure > to submit patches if I spot something that could help reduce stack > usage. Most of the low hanging fruit is already gone. The problem we are facing now for further reductions in stack usage is the fact that we need to factor code. That is a major undertaking and has a _lot_ of risk associated with it....
I'll try to spot some of the remaining low hanging fruit ;)
> >There is active discussion about reducing inlining: > >http://bugzilla.kernel.org/show_bug.cgi?id=7364 > > Thanks, I'll check that out. That's one of the few remaining low hanging fruit, and that's fixed in the patches I already have.
Nice. Will be good to get that in.
> >Thanks for traces, I've captured this information. > > > You are welcome. If you want/need more traces then I've got ~2.1G > worth of traces that you can have :) Well, we don't need that many, but it would be nice to have a set of unique traces that lead to overflows - could you process them in some way just to extract just the unique XFS traces that occur?
I'll try to extract a copy of each unique trace that involves xfs, sometime tomorrow or the day after, and then send you the result. -- Jesper Juhl <jesper.juhl@xxxxxxxxx> Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html Plain text mails only, please http://www.expita.com/nomime.html - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
