Re: 2.1.127 BUGS was Re: Linux-2.1.127

Andi Kleen (ak@muc.de)
Mon, 9 Nov 1998 19:02:24 +0100


[Sorry for the late answer]

On Sun, Nov 08, 1998 at 07:54:50PM +0100, Linus Torvalds wrote:
>
>
> On 8 Nov 1998, Andi Kleen wrote:
> >
> > I still see two mm/scheduling bugs with 2.1.127:
> >
> > - kswapd is far too aggressive at killing the page cache. Assuming I run
> > a normal SMP X11 setup with 128MB and most of the memory used in the page
> > cache (about 60%). Now I start a kernel compile with -j4. The result is that
> > nearly all of the page cache is freed after a few seconds (it runs with >50%
> > free memory then), then when it continues compiling the page cache slowly
> > builds up again, then after about 30s is completely blow away again etc.
>
> Ok, this is due to having _only_ a time limit for kswapd - I've known all
> along that that was wrong, but it works for me with tons of memory, and I
> wanted to have people be able to actually compare. So the thing I'd like
> you to compare against and try is simply:

>
> mm/vmscan.c, around like 540:
>
> /* max one hundreth of a second */
> end_time = jiffies + (HZ-1)/100;
> do {
> if (!do_try_to_free_page(0))
> break;
> + if (nr_free_pages > 2*freepages.high)
> + break;
> } while (time_before_eq(jiffies,end_time));
>

It helps a bit, but doesn't fix the problem completely: the computer
still runs with 20-30MB free, and sometimes there are spikes when upto 60-70MB
are freed and the page cache is killed.

My freepages.high setting (default as set by the kernel) is 768

Also why use 2*freepages.high? Wouldn't it be better to just double the
parameter initially so that the user can tune it?

-Andi

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