David Chinner wrote:
On Fri, Dec 01, 2006 at 07:22:18PM +0000, Lachlan McIlroy wrote:
David Chinner wrote:
On Thu, Nov 30, 2006 at 06:03:40PM +0000, Lachlan McIlroy wrote:
I think the slow path code is somewhat clearer with a separate
mutex - it clearly documents the serialisation barrier that
the slow path uses and allows us to do slow path checks on the
per-cpu counters without needing the SB_LOCK.
It's certainly an improvement over the original code.
It also means that in future, we can slowly remove the need for
holding the SB_LOCK across the entire rebalance operation and only
use it when referencing the global superblock fields during
If the need arises, it also means we can move to a mutex per counter
so we can independently rebalance different types of counters at the
same time (which we can't do right now).
That seems so obvious - I'm surprised we can't do it now.
Well, the reason I didn't go down this path in the first place
was that typically only one type of counter would need rebalancing
at a time (e.g. free blocks or free inodes, but not both at the
same time). I tested this out on revenue2 with simultaneous creates
and deletes of small files but could not cause contention on the
single global lock under these loads. i also tried parallel
writes of large files with creates and deletes, but hte create/delete
was slowed sufficiently by the parallel writes that it once again
didn't cause an issue.
Hence it didn't seem to be an issue and a single lock simplified
the initial implementation. What I'm thinking now is that it may
become an issue with MDFS as acheivable create and delete rates
should be much higher on one of these filesystems and then it may
prove to be an issue.
just updated my CVS copy from oss.sgi.com ( the linux-2.6-xfs ) and
tried to compile ... but your patch failes to compile if HAVE_PERCPU_SB
is #ifndef'd :-(, the m_icsb_mutex is not in the struct see xfs_mount.h.
Make oldconfig didn't show HAVE_PERCPU_SB as option for .config, looks
like nobody tested on a single processor config ??
Mit freundlichen Grüssen / best regards
Klaus Strebel, Dipl.-Inform. (FH), mailto:klaus.strebel@xxxxxxx
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