On Mon, Jun 18, 2012 at 04:11:52PM -0500, Eric Sandeen wrote: > On 6/18/12 1:25 PM, 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 > > well, 8k on x86_64 (not 4k) right? But still... > > Maybe it's still a partial hack but it's more generic - should we have > IRQ stacks like x86 has? (I think I'm right that that only exists > on x86 / 32-bit) - is there any downside to that? We already have irq stacks for x86-64 - the stackunwinder knows about them so when you get a stack trace from the interrupt stack is walks back across to the thread stack at the appropriate point... See dump_trace() in arch/x86/kernel/dumpstack_64.c Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- 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
