https://bugzilla.novell.com/show_bug.cgi?id=879071
https://bugzilla.novell.com/show_bug.cgi?id=879071#c15
--- Comment #15 from Michal Hocko
we can clearly see that dirtier is ~24k pages ahead of writeback on average which is ~90M so around 2s worth of writeback. Correct. And that is really working as designed - we have dirty_bytes set to 200 MB so writeback is free to keep upto 200 MB of dirty pages if it sees that fit. We have to keep non-trivial amount of dirty pages in order to be able to
(In reply to comment #13) [...] form large enough IOs and keep hardware busy. The experiments have shown that you need at least a second or so worth of writeback cached to level out bumps in disk performance, IO completion bursts etc.
Thanks for the clarification.
Btw. I do not see dirty throttling checking global_dirtyable_memory if dirty_bytes is used. Is this OK? I am not sure. The idea has been that when dirty_bytes is set at X, then you know you can have X amount of dirty memory.
OK, I suspected something like this. But I am afraid that more we will encourage users to use dirty_bytes because dirty_ratio sucks with a lot of memory the more strange issues we will see.
However when global_dirtyable_memory() is less than say 2*dirty_bytes, it gets really strange and maybe we should take that into account. I guess you can try proposing something like that upstream (or I can :).
I guess this can be double checked by setting dirty_ratio to 4% to have the similar setting except that global_dirtyable_memory is not ignored. Could you give it a try Jiri? -- Configure bugmail: https://bugzilla.novell.com/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are on the CC list for the bug.