In the log I see things like:

    2017-09-13 03:54:33 init message: Rescanning...
    2017-09-13 03:54:33 Rescanning last 68616 blocks (from block 416339)...
    2017-09-13 03:54:40 AddToWallet xxxxx  update
    2017-09-13 03:55:33 Still rescanning. At block 418849. Progress=0.549138

I would be interested to see the wallet file name on each of these log lines.

Would there be any interest in merging such a PR?
if (outgoing && IsChange(out)) {
                debit -= out.nValue;
            } else if (IsMine(out) & filter && depth >= minDepth && (!account || *account == GetLabelName(out.scriptPubKey))) {
                balance += out.nValue;
            }
        }
        
        if (outgoing && (!account || *account == wtx.strFromAccount)) {
            balance -= debit;
        }
    }
    if (account) {
        balance += WalletBatch(*database).GetAccountCreditDebit(*account);
    }
    return balance;
}
CAmount CWallet::GetAvailableBalance(const CCoinControl* coinControl) const
{
    LOCK2(cs_main, cs_wallet);
    CAmount balance = 0;
    std::vector<COutput> vCoins;
    AvailableCoins(vCoins, true, coinControl);
    for (const COutput& out : vCoins) {
        if (out.fSpendable) {
            balance += out.tx->tx->vout[out.i].nValue;
        }
    }
    return balance;
}
void CWallet::AvailableCoins(std::vector<COutput> &vCoins, bool fOnlySafe, const CCoinControl *coinControl, const CAmount &nMinimumAmount, const CAmount &nMaximumAmount, const CAmount &nMinimumSumAmount, const uint64_t nMaximumCount, const int nMinDepth, const int nMaxDepth) const