On 09/13/2011 09:23 PM, Andreas Dilger wrote:
On 2011-09-13, at 7:29 PM, Yongqiang Yang wrote:
On Wed, Sep 14, 2011 at 2:33 AM, Allison Henderson
<achender@xxxxxxxxxxxxxxxxxx> wrote:
Hi All,
I have been trying to find a way to synchronize punch hole with read and
write operations with out the use of i_mutex. The concern is that after
punch hole has released the pages inside the hole, another process may remap
the page to a block before punch has taken i_data_sem. I think putting
i_mutex around the punch hole operation would fix this, but since we are
trying to avoid further improper use of i_mutex, I am trying to avoid that
solution.
I cannot use i_data_sem to protect the pages because it seems most of the
code has already established a locking order of pages first, then
i_data_sem. So moving i_data_sem up tends to cause a lot of dead locks.
I'm thinking that there probably needs to be a another mutex involved some
where, but I wasnt sure if some one is already working on the idea of
introducing a replacement for i_mutex. So I just wanted to know if there
are any plans already in motion for this, or if any one else could suggest
some ideas for the punch hole issue. Thx all!
Lukas sent out a patch ([PATCH] ext4: Make reads/writes atomic with
i_rwlock semaphore) which collected some feedbacks suggesting using
extent lock instead of a read-write semaphore. If there is extent
lock implementation in ext4, then fallocate can use it, maybe
dioread-nolock can use it as well, e.g. locking a range and unlocking
the range until the extent is converted from unwritten to init.
We have a prototype patch for extent locking for ext4. We are planning to
use this for parallel locking of htree directories, but it could potentially
be modified to for extent locking of files.
The current patch is below, but it hasn't gone through a lot of testing:
http://review.whamcloud.com/#patch,sidebyside,375,2,ldiskfs/kernel_patches/patches/ext4_pdirop-rhel6.patch
Cheers, Andreas
Alrighty then, I will have a look at the existing patches. Thx!
Allison Henderson
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