On 02/07/2017 10:25 PM, Shaohua Li wrote:
> 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.
This flag is set iff PPL is enabled, so this function would only check
the flag anyway. But I can add it to improve readability.
>> 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.
In PPL metadata we don't store information about which drives we write
to, only the modified data range. For a single stripe_head we can only
have one PPL entry at a time, which describes one data range. This can
be improved in the future, but will require extending the PPL metadata.
Thanks,
Artur
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