Improved writeback management

1. 现象

Since the dawn of time, the way Linux synchronizes to disk the data written to memory by processes (aka. background writeback) has sucked. When Linux writes all that data in the background, it should have little impact on foreground activity. That's the definition of background activity...But for a long as it can be remembered, heavy buffered writers have not behaved like that. For instance, if you do something like $ dd if=/dev/zero of=foo bs=1M count=10k, or try to copy files to USB storage, and then try and start a browser or any other large app, it basically won't start before the buffered writeback is done, and your desktop, or command shell, feels unreponsive. These problems happen because heavy writes -the kind of write activity caused by the background writeback- fill up the block layer, and other IO requests have to wait a lot to be attended (for more details, see the LWN article)
Linux 4.10 releasenote

2. 现状

在此问题社区patch以前,也经常遇到过,但是当时没在意。前段日子使用ubuntu桌面的时候,当打开chrome,firefox的tab很多事,就出现好多打开很慢的,同时GUI变灰进而变黑,thunderbird 脚本停止运行等现象。






3. 过程



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