$350bn of Treasuries traded on 24 November, $182bn of which were sold by dealers to customers [1]. Two days prior, $220bn of stocks traded on the Nasdaq alone [2].

China could liquidate its $820bn of Treasuries [3] in a couple months without throwing the market out of whack.

[1] https://cdn.finra.org/trace/treasury-aggregates/daily/ts-dai...

[2] http://www.nasdaqtrader.com/Trader.aspx?id=DailyMarketSummar...

[3] https://www.reuters.com/markets/us/foreign-holdings-us-treas...

21B isn't much in the grand scheme of things. But the 10 year treasury yield went to 5%. A historical high. It was noticed.