Re: [PATCH] Separate global/perzone inactive/free shortage

[Kanoj Sarcar]

--- Marcelo Tosatti <[e-mail]> wrote:
> Hi,
> 
> As well known, the VM does not make a distiction
> between global and
> per-zone shortages when trying to free memory. That
> means if only a given
> memory zone is under shortage, the kernel will scan
> pages from all zones. 
> 
> The following patch (against 2.4.6-ac2), changes the
> kernel behaviour to
> avoid freeing pages from zones which do not have an
> inactive and/or
> free shortage.
> 
> Now I'm able to run memory hogs allocating 4GB of
> memory (on 4GB machine)
> without getting real long hangs on my ssh session.
> (which used to happen
> on stock -ac2 due to exhaustion of DMA pages for
> networking).
> 
> Comments ? 
> 
> Dirk, Can you please try the patch and tell us if it
> fixes your problem ? 
> 
> 

Just a quick note. A per-zone page reclamation
method like this was what I had advocated and sent
patches to Linus for in the 2.3.43 time frame or so.
I think later performance work ripped out that work.
I guess the problem is that a lot of the different
page reclamation schemes first of all do not know
how to reclaim pages for a specific zone, and secondly
have to go thru a lot of work before they discover the
page they are trying to reclaim does not belong to the
shortage zone, hence wasting a lot of work/cputime.
try_to_swap_out is a good example, which can be solved
by rmaps. 

Kanoj

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