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

Alex Tomas
2007-05-04T06:57:41Z

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