Hey Andreas, On Mon, Jun 18, 2012 at 12:25:37PM -0600, Andreas Dilger wrote: > On 2012-06-18, at 6:08 AM, Christoph Hellwig wrote: > > May saw the release of Linux 3.4, including a decent sized XFS update. > > Remarkable XFS features in Linux 3.4 include moving over all metadata > > updates to use transactions, the addition of a work queue for the > > low-level allocator code to avoid stack overflows due to extreme stack > > use in the Linux VM/VFS call chain, > > This is essentially a workaround for too-small stacks in the kernel, > which we've had to do at times as well, by doing work in a separate > thread (with a new stack) and waiting for the results? This is a > generic problem that any reasonably-complex filesystem will have when > running under memory pressure on a complex storage stack (e.g. LVM + > iSCSI), but causes unnecessary context switching. > > Any thoughts on a better way to handle this, or will there continue > to be a 4kB stack limit and hack around this with repeated kmalloc > on callpaths for any struct over a few tens of bytes, implementing > memory pools all over the place, and "forking" over to other threads > to continue the stack consumption for another 4kB to work around > the small stack limit? FWIW, I think your characterization of the problem as a 'workaround for too-small stacks in the kernel' is about right. I don't think any of the XFS folk were very happy about having to do this, but in the near term it doesn't seem that we have a good alternative. I'm glad to see that there are others with the same pain, so maybe we can build some support for upping the stack limit. Regards, Ben -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
