Memory swap when there's apparently plenty of free RAM

[Eli Billauer]

I was slightly ambiguous there: I launched Chrome (it wasn't running 
previously).

And even though I didn't check the amount of swap space before, it never 
exceeds a few MBs.

So it definitely looks like the swappiness parameter was the thing to 
fix on a system that shouldn't ever use swap under normal conditions.

    Eli

On 06/18/2012 05:21 PM, Nadav Har'El wrote:
> On Mon, Jun 18, 2012, Eli Billauer wrote about "Memory swap when there's apparently plenty of free RAM":
>    
>> When I opened Google Chrome last (I don't use it a lot), the
>> computer froze completely for a minute, no mouse movement, no
>> response to CTRL-Alt-F2, and the clock didn't change. The hard disk
>> was highly active. After that minute, all resumed to normal, and the
>> Chrome browser started as if nothing had just happened.
>>
>> It then turned out that 2 GB of RAM had been swapped to disk.
>>      
> I'm not sure I understood - when you say "opened Google Chrome", was
> Chrome already running for a long time at that point (sitting somewhere
> in the background), or did you run it anew?
>
> Also, when you say "it turned out that 2 GB of RAM had been swapped to
> disk", I assume you really know that before using chrome it was 0
> swapped out, and when you used chrome it jumped to 2 GB - rather what
> you know is only that it was 2GB after?
>
> I the answers are that 1. Google Chrome was already running for a long time
> (it wasn't a new run), and 2. You don't know what was the swap situation
> a moment before using Chrome, then I may have an explanation.
> (see http://lwn.net/Articles/83588/ for more info, and it also explains
> the "swappiness" parameter that Muli pointed to).
>
> It is possible that some time earlier, some process accessed many
> gigabytes of files. Perhaps you had some backup process running during
> the previous night. Or perhaps you did a large "yum update" earlier
> (though Fedora 12 doesn't get updates any more ;-)). Or perhaps you
> have a file server on your machine, or you watched a large movie.
> I don't know. The point is that Chrome has been idle for many hours, not
> touching any of its memory, and at some point Linux may have decided
> that instead of keeping it in memory, it's better to swap it out and
> use the extra memory for caching more files which were accessed by your
> backup/server/movie-watching or whatever.
>
> Then, when you came back and touched Chrome, not only did it need to
> swap in many of Chrome pages, it also had to read from disk many clean
> pages - parts of the chrome executable (it's a 70 MB wopper of an
> executable) and parts of the 71 (!!!) shared libraries that Chrome
> depends on, and so on. Since all of this isn't likely to be contiguous
> on disk, it can cause a huge number of seeks, and be very slow.
>
> Just a guess....
>
>
>    



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