>> >
>> > diff -Nrup linux-2.6.27-rc1.org/fs/jbd/transaction.c
>linux-2.6.27-rc1/fs/jbd/transaction.c
>> > --- linux-2.6.27-rc1.org/fs/jbd/transaction.c 2008-07-29
>19:28:47.000000000 +0900
>> > +++ linux-2.6.27-rc1/fs/jbd/transaction.c 2008-07-29 20:40:12.000000000 +0900
>> > @@ -1764,6 +1764,12 @@ int journal_try_to_free_buffers(journal_
>> > */
>> > if (ret == 0 && (gfp_mask & __GFP_WAIT) && (gfp_mask & __GFP_FS)) {
>> > journal_wait_for_transaction_sync_data(journal);
>> > +
>> > + bh = head;
>> > + do {
>> > + while (atomic_read(&bh->b_count))
>> > + schedule();
>> > + } while ((bh = bh->b_this_page) != head);
>> > ret = try_to_free_buffers(page);
>> > }
>>
>> The loop is problematic. If the scheduler decides to keep running this
>> task then we have a busy loop. If this task has realtime policy then
>> it might even lock up the kernel.
>>
>
>ocfs2 calls journal_try_to_free_buffers too, looping on b_count might
>not be the best idea there either.
>
>This code gets called from releasepage, which is used other places than
>the O_DIRECT invalidation paths, I'd be worried about performance
>problems here.
>
try_to_release_page has gfp_mask parameter. So when try_to_releasepage
is called from performance sensitive part, gfp_mask should not be set.
b_count check loop is inside of (gfp_mask & __GFP_WAIT) && (gfp_mask & __GFP_FS) check.
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