Re: XFS status update for May 2012

Eric Sandeen
2012-06-18T21:16:14Z

On 6/18/12 4:11 PM, 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?

Maybe I'm wrong about that, and we already have IRQ stacks on x86_64 -
at least based on the kernel documentation?

-Eric