On Mon, Jan 30, 2017 at 07:59:48PM +0100, Artur Paszkiewicz wrote:
> Attach a page for holding the partial parity data to stripe_head.
> Allocate it only if mddev has the MD_HAS_PPL flag set.
>
> Partial parity is the xor of not modified data chunks of a stripe and is
> calculated as follows:
>
> - reconstruct-write case:
> xor data from all not updated disks in a stripe
>
> - read-modify-write case:
> xor old data and parity from all updated disks in a stripe
>
> Implement it using the async_tx API and integrate into raid_run_ops().
> It must be called when we still have access to old data, so do it when
> STRIPE_OP_BIODRAIN is set, but before ops_run_prexor5(). The result is
> stored into sh->ppl_page.
>
> Partial parity is not meaningful for full stripe write and is not stored
> in the log or used for recovery, so don't attempt to calculate it when
> stripe has STRIPE_FULL_WRITE.
>
> Signed-off-by: Artur Paszkiewicz <artur.paszkiewicz@xxxxxxxxx>
> ---
> drivers/md/raid5.c | 98 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> drivers/md/raid5.h | 2 ++
> 2 files changed, 100 insertions(+)
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index d1cba941951e..e1e238da32ba 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -466,6 +466,11 @@ static void shrink_buffers(struct stripe_head *sh)
> sh->dev[i].page = NULL;
> put_page(p);
> }
> +
> + if (sh->ppl_page) {
> + put_page(sh->ppl_page);
> + sh->ppl_page = NULL;
> + }
> }
>
> static int grow_buffers(struct stripe_head *sh, gfp_t gfp)
> @@ -482,6 +487,13 @@ static int grow_buffers(struct stripe_head *sh, gfp_t gfp)
> sh->dev[i].page = page;
> sh->dev[i].orig_page = page;
> }
> +
> + if (test_bit(MD_HAS_PPL, &sh->raid_conf->mddev->flags)) {
I think the test should be something like:
if (raid5_ppl_enabled())
Having the feature doesn't mean the feature is enabled.
> pr_debug("%s: stripe %llu locked: %d ops_request: %lx\n",
> __func__, (unsigned long long)sh->sector,
> s->locked, s->ops_request);
> @@ -3105,6 +3175,34 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx,
> if (*bip && (*bip)->bi_iter.bi_sector < bio_end_sector(bi))
> goto overlap;
>
> + if (forwrite && test_bit(MD_HAS_PPL, &conf->mddev->flags)) {
> + /*
> + * With PPL only writes to consecutive data chunks within a
> + * stripe are allowed. Not really an overlap, but
> + * wait_for_overlap can be used to handle this.
> + */
Please describe why the data must be consecutive.
Thanks,
Shaohua
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