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Increment zil_itx_needcopy_bytes properly #7176

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Mar 2, 2018
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Increment zil_itx_needcopy_bytes properly #7176

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3 changes: 1 addition & 2 deletions module/zfs/zil.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1461,8 +1461,7 @@ zil_lwb_commit(zilog_t *zilog, itx_t *itx, lwb_t *lwb)
lrw->lr_offset += dnow;
lrw->lr_length -= dnow;
ZIL_STAT_BUMP(zil_itx_needcopy_count);
ZIL_STAT_INCR(zil_itx_needcopy_bytes,
lrw->lr_length);
ZIL_STAT_INCR(zil_itx_needcopy_bytes, dnow);
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This same change should be made when incrementing the zil_itx_copied_bytes above and zil_itx_indirect_bytes below. They can't underflow in the same way but dnow is the accurate length to use.

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dnow will always be zero in those cases because itx_wr_state != WR_NEED_COPY:


        if (lrc->lrc_txtype == TX_WRITE && itx->itx_wr_state == WR_NEED_COPY) {
                dlen = P2ROUNDUP_TYPED(
                    lrw->lr_length, sizeof (uint64_t), uint64_t);
        } else {
                dlen = 0;
        }
        ...
        dnow = MIN(dlen, lwb_sp - reclen);
        ...
               if (itx->itx_wr_state == WR_COPIED) {
                        ZIL_STAT_BUMP(zil_itx_copied_count);
>>>                     ZIL_STAT_INCR(zil_itx_copied_bytes, lrw->lr_length);
                } else {
                ...
                       if (itx->itx_wr_state == WR_NEED_COPY) {
                                ...
                        } else {
                                ASSERT3S(itx->itx_wr_state, ==, WR_INDIRECT);
                                dbuf = NULL;
                                ZIL_STAT_BUMP(zil_itx_indirect_count);
>>>                             ZIL_STAT_INCR(zil_itx_indirect_bytes,
>>>                                lrw->lr_length);
                        }

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I think the simple change is better than where we are now (dnow? :-)

I'd like to consider recording both dnow and lr_length, but that should be a separate PR, if and when it proves useful. And I'd like to move any test case to the separate PR.

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@chrisrd good point! OK, then this LGTM and nice job reproducing the issue to veirfy the fix.

} else {
ASSERT3S(itx->itx_wr_state, ==, WR_INDIRECT);
dbuf = NULL;
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