Re: More memory more jitters?

[Duncan <1i5t5.duncan@cox.net>]

Hugo Mills posted on Sat, 14 Nov 2015 14:31:12 +0000 as excerpted:

>> I have read the Gotcha[1] page:
>> 
>>    Files with a lot of random writes can become heavily fragmented
>> (10000+ extents) causing trashing on HDDs and excessive multi-second
>> spikes of CPU load on systems with an SSD or **large amount a RAM**.
>> 
>> Why could large amount of memory worsen the problem?
> 
>    Because the kernel will hang on to lots of changes in RAM for
> longer. With less memory, there's more pressure to write out dirty pages
> to disk, so the changes get written out in smaller pieces more often.
> With more memory, the changes being written out get "lumpier".
> 
>> If **too much** memory is a problem, is it possible to limit the memory
>> btrfs use?
> 
>    There's some VM knobs you can twiddle, I believe, but I haven't
> really played with them myself -- I'm sure there's more knowledgable
> people around here who can suggest suitable things to play with.

Yes.  Don't have time to explain now, but I will later, if nobody beats 
me to it.



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"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman