Shaohua Li <shli@xxxxxx> writes:
> Since superblock is updated infrequently, we do a simple trim of log
> disk (a synchronous trim)
>
> Signed-off-by: Shaohua Li <shli@xxxxxx>
> ---
> drivers/md/raid5-cache.c | 44 +++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 43 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
> index a02f9ce..afc3b6b 100644
> --- a/drivers/md/raid5-cache.c
> +++ b/drivers/md/raid5-cache.c
> @@ -654,6 +654,48 @@ static void r5l_kick_io_unit(struct r5l_log *log)
> }
>
> static void r5l_write_super(struct r5l_log *log, sector_t cp);
> +static void r5l_write_super_and_discard_space(struct r5l_log *log,
> + sector_t end)
> +{
> + struct block_device *bdev = log->rdev->bdev;
> + struct mddev *mddev;
> +
> + r5l_write_super(log, end);
> +
> + if (!blk_queue_discard(bdev_get_queue(bdev)))
> + return;
> +
> + /* discard destroy old data in log, so force a super update */
> + mddev = log->rdev->mddev;
> + /*
> + * mddev->thread could be shut down already in raid array stop. At that
> + * time, we should already lock reconfig_mutex
> + * */
> + if (!mddev->thread) {
> + WARN_ON(!mddev_is_locked(mddev));
> + md_update_sb(mddev, 1);
> + } else {
> + set_bit(MD_CHANGE_PENDING, &mddev->flags);
> + md_wakeup_thread(mddev->thread);
> + wait_event(mddev->sb_wait,
> + !test_bit(MD_CHANGE_PENDING, &mddev->flags));
> + }
I didn't like this. It looks clumsy to me.
So I went to have a look at the code to understand why it was needed.
I found that r5l_exit_log() was being called from free_conf().
I didn't notice that before.
->free() is only supposed to free, not write anything. It could be too
late to write anything.
You need to get the raid5_quiesce(1) call to stablise the array. It can
do the final r5l_do_reclaim().
So it is OK for free_conf to call r5l_exit_log as long as it only
deregisters the thread and frees the data structures.
The "r5l_do_reclaim" needs to be moved out.
I wonder where the md_update_sb() should go...
We currently calls "stop_writes" and then "mddev_detach".
So we shouldn't be writing anything by the time we get to mddev_detach,
but in there we wait for writes to complete. That looks wrong.
I might move some of that stuff from mddev_detach to __md_stop_writes.
Then md_stop_writes can call ->quiesce and then md_update_sb(). That is
enough for raid5-cache to just call r5l_do_reclaim in raid5_quiesce, and
have the md_update_sb() called at the right time.
I'll see if i can make that work.
Thanks,
NeilBrown
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