>
> On Wed, 12 Jan 2000, Kanoj Sarcar wrote:
>
> > --- mm/page_alloc.c Tue Jan 11 11:00:31 2000
> > +++ mm/page_alloc.c Tue Jan 11 23:59:35 2000
> > + cumulative += size;
> > + mask = (cumulative >> 7);
> > + if (mask < 1) mask = 1;
> > + zone->pages_low = mask*2;
> > + zone->pages_high = mask*3;
> > zone->low_on_memory = 0;
>
> I think that busier machines probably have a larger need
> for DMA memory than this code fragment will give us. I
> have the gut feeling that we'll want to keep about 512kB
> or more free in the lower 16MB of busy machines...
Note that as I point out in my documentation, and as Alan
also points out, 2.2 is doing fine. The 2.2 code does not
guarantee dma-zone balancing even if it is empty (if there
is enough regular free pages). Which means all dma requests
will fail. I have tried to fix that, since with HIGHMEM,
the problem is actually more aggravated.
My aim is to fix a couple of problems, move to a zone based
balancing, and then maybe finetune it. For example, the
>> 7 part can be replaced with >> N, where N is dependent
on the zone type, or size of lower zones, etc. I mention this
in the doc too. The only problem is, if N < 7, you will probably
have degraded perfomance in certain cases due to more frequent
balancing.
>
> (if only because such a large amount of free pages in
> such a small part of the address space will give us
> higher-order free pages)
I note that Andrea also commented about this. I am also
of the same opinion as him, we should not (as far as possible)
try to intermingle unrelated issues. In this case though,
I have no idea how having a large number of free dma pages
ensures more higher-order free pages. Can someone give me
the logic for this claim?
>
> > --- mm/vmscan.c Tue Jan 11 11:00:31 2000
> > +++ mm/vmscan.c Tue Jan 11 23:29:41 2000
> > @@ -534,8 +534,11 @@
> > int retval = 1;
> >
> > wake_up_process(kswapd_process);
> > - if (gfp_mask & __GFP_WAIT)
> > + if (gfp_mask & __GFP_WAIT) {
> > + current->flags |= PF_MEMALLOC;
> > retval = do_try_to_free_pages(gfp_mask, zone);
> > + current->flags &= ~PF_MEMALLOC;
> > + }
> > return retval;
> > }
>
> Please note that kswapd still exits when the total number
> of free pages in the system is high enough. Balancing can
> probably better be done in the background by kswapd than
> by applications that happen to stumble across a nonbalanced
> zone...
Yes, we need to decide whether kswapd needs modification too. Its
just that I want to do incremental fixes, instead of change a
huge bunch of code all at once. The question is, if I had a Linux
2.3 kernel, where I had completely deleted kswapd(), what problems
would the kernel face? Ie, what is kswapd()'s purpose?
Kanoj
>
> regards,
>
> Rik
> --
> The Internet is not a network of computers. It is a network
> of people. That is its real strength.
>
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