On 03/10/2017 12:24 AM, Shaohua Li wrote:
> On Thu, Mar 09, 2017 at 09:59:59AM +0100, Artur Paszkiewicz wrote:
>> Implement the calculation of partial parity for a stripe and PPL write
>> logging functionality. The description of PPL is added to the
>> documentation. More details can be found in the comments in raid5-ppl.c.
>>
>> 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.
>>
>> Put the PPL metadata structures to md_p.h because userspace tools
>> (mdadm) will also need to read/write PPL.
>>
>> Warn about using PPL with enabled disk volatile write-back cache for
>> now. It can be removed once disk cache flushing before writing PPL is
>> implemented.
>>
>> Signed-off-by: Artur Paszkiewicz <artur.paszkiewicz@xxxxxxxxx>
>
> ... snip ...
>
>> +struct dma_async_tx_descriptor *
>> +ops_run_partial_parity(struct stripe_head *sh, struct raid5_percpu *percpu,
>> + struct dma_async_tx_descriptor *tx)
>> +{
>> + int disks = sh->disks;
>> + struct page **xor_srcs = flex_array_get(percpu->scribble, 0);
>> + int count = 0, pd_idx = sh->pd_idx, i;
>> + struct async_submit_ctl submit;
>> +
>> + pr_debug("%s: stripe %llu\n", __func__, (unsigned long long)sh->sector);
>> +
>> + /*
>> + * Partial parity is the XOR of stripe data chunks that are not changed
>> + * during the write request. Depending on available data
>> + * (read-modify-write vs. reconstruct-write case) we calculate it
>> + * differently.
>> + */
>> + if (sh->reconstruct_state == reconstruct_state_prexor_drain_run) {
>> + /* rmw: xor old data and parity from updated disks */
>> + for (i = disks; i--;) {
>> + struct r5dev *dev = &sh->dev[i];
>> + if (test_bit(R5_Wantdrain, &dev->flags) || i == pd_idx)
>> + xor_srcs[count++] = dev->page;
>> + }
>> + } else if (sh->reconstruct_state == reconstruct_state_drain_run) {
>> + /* rcw: xor data from all not updated disks */
>> + for (i = disks; i--;) {
>> + struct r5dev *dev = &sh->dev[i];
>> + if (test_bit(R5_UPTODATE, &dev->flags))
>> + xor_srcs[count++] = dev->page;
>> + }
>> + } else {
>> + return tx;
>> + }
>> +
>> + init_async_submit(&submit, ASYNC_TX_XOR_ZERO_DST, tx, NULL, sh,
>> + flex_array_get(percpu->scribble, 0)
>> + + sizeof(struct page *) * (sh->disks + 2));
>
> Since this should be done before biodrain, should this add ASYNC_TX_FENCE flag?
The result of this calculation isn't used later by other async_tx
operations, so it's not needed here, if I understand this correctly. But
maybe later we could optimize and use partial parity to calculate full
parity, then it will be necessary.
Thanks,
Artur
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