Re: [PATCH] swapin readahead

[Zlatko Calusic <Zlatko.Calusic@CARNet.hr>]

ebiederm+eric@ccr.net (Eric W. Biederman) writes:

> >>>>> "ZC" == Zlatko Calusic <Zlatko.Calusic@CARNet.hr> writes:
> 
> ZC> Trying 2.1.131-2, I'm mostly satisfied with MM workout, but...
> 
> ZC> Still, I have a feeling that limit imposed on cache growth is now too
> ZC> hard, unlike kernels from the 2.1.1[01]? era, that had opposite
> ZC> problems (excessive cache growth during voluminous I/O operations).
> 
> My gut reaction is that we need a check in swap_out to see if we have
> written out a swap_cluster or some other indication that we have
> started all of the disk i/o that is reasonable for now and need to
> switch to something else.

I tried that approach (Rik has tried also) but only to find that
swapout speed drops. Will investigate further...

> 
> This should have the same effect as the switches with the limits on
> the swap cache but more autobalancing.  I'm nervous of a kernel that
> needs small limits on it's disk cache to work correctly.

Yes, that is exactly my point.

I'm glad there is at least one person to share an opinion with. :)

> 
> ZC> What I wanted to ask is: do you guys share my opinion, and what
> ZC> changes would you like to see before 2.2 comes out?
> 
> One thing worth putting in.  Probably before to 2.2 but definentily
> before any swap page readahead is done is to start using brw_page
> for swapfiles.  I don't know about synchronous cases, but in the when
> asynchronous operation is important it improves swapfile performance
> immensely.
> 

Speaking about swap files (as opposed to swap partitions) what is the
reason for synchronous operation when swapping to them, at first
place? Races?

-- 
Posted by Zlatko Calusic           E-mail: <Zlatko.Calusic@CARNet.hr>
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