Re: [PATCH] swap: send callback when swap slot is freed

[Nitin Gupta]

On 08/17/2009 08:25 AM, KAMEZAWA Hiroyuki wrote:
> On Wed, 12 Aug 2009 20:07:43 +0530
> Nitin Gupta<ngupta@xxxxxxxxxx>  wrote:
>
> > Currently, we have "swap discard" mechanism which sends a discard bio request
> > when we find a free cluster during scan_swap_map(). This callback can come a
> > long time after swap slots are actually freed.
> >
> > This delay in callback is a great problem when (compressed) RAM [1] is used
> > as a swap device. So, this change adds a callback which is called as
> > soon as a swap slot becomes free. For above mentioned case of swapping
> > over compressed RAM device, this is very useful since we can immediately
> > free memory allocated for this swap page.
> >
> > This callback does not replace swap discard support. It is called with
> > swap_lock held, so it is meant to trigger action that finishes quickly.
> > However, swap discard is an I/O request and can be used for taking longer
> > actions.
> >
> > Links:
> > [1] http://code.google.com/p/compcache/
>
> Hmm, do you really need notify at *every* swap free ?
> No batching is necessary ?

We need notify for every swap free and no batching is desired, at least for 
compcache case.

Thanks,
Nitin
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