Re: [ext3][kernels >= 2.6.20.7 at least] KDE going comatose when FS is under heavy write load (massive starvation)

[Alex Tomas <alex@clusterfs.com>]

Andrew Morton wrote:
> On Fri, 04 May 2007 10:18:12 +0400 Alex Tomas <alex@clusterfs.com> wrote:
> 
>> Andrew Morton wrote:
>>> Yes, there can be issues with needing to allocate journal space within the
>>> context of a commit.  But
>> no-no, this isn't required. we only need to mark pages/blocks within
>> transaction, otherwise race is possible when we allocate blocks in transaction,
>> then transacton starts to commit, then we mark pages/blocks to be flushed
>> before commit.
> 
> I don't understand.  Can you please describe the race in more detail?

if I understood your idea right, then in data=ordered mode, commit thread writes
all dirty mapped blocks before real commit.

say, we have two threads: t1 is a thread doing flushing and t2 is a commit thread

t1					t2
find dirty inode I
find some dirty unallocated blocks
journal_start()
allocate blocks
attach them to I
journal_stop()

					going to commit
					find inode I dirty
					do NOT find these blocks because they're
					  allocated only, but pages/bhs aren't mapped
					  to them
					start commit


map pages/bhs to just allocate blocks


so, either we mark pages/bhs someway within journal_start()--journal_stop() or
commit thread should do lookup for all dirty pages. the latter doesn't sound nice, IMHO.

thanks, Alex