Re: [ck] lowmem_reserve question

[Con Kolivas <kernel@kolivas.org>]

On Mon, 3 Apr 2006 12:48 pm, Con Kolivas wrote:
> While trying to digest just what the lowmem_reserve does 
> and how it's utilised I looked at some of the numbers
>
> int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1] = { 256, 256, 32 };
>
> lower_zone->lowmem_reserve[j] = present_pages /
> sysctl_lowmem_reserve_ratio[idx];
>
> This is interesting because there are no bounds on this value and it seems
> possible to set the sysctl to have a lowmem_reserve that is larger than the
> zone size. Ok that's a sysctl so if a user is setting it wrongly that's
> their fault... or should there be some upper bound?
>
> Furthermore, now that we have the option of up to 3GB lowmem split on 32bit
> we can have a default lowmem_reserve of almost 12MB (if I'm reading it
> right) which seems very tight with only 16MB of ZONE_DMA.
>
> On a basically idle 1GB lowmem box that I have it looks like this:
>
> Node 0, zone      DMA
>   pages free     1025
>         min      15
>         low      18
>         high     22
>         active   2185
>         inactive 0
>         scanned  555 (a: 21 i: 6)
>         spanned  4096
>         present  4096
>         protection: (0, 0, 1007, 1007)
>
> With 3GB lowmem the default settings seem too tight to me. The way I see
> it, there should be some upper bounds on the lowmem reserves. Or perhaps
> I'm just missing something again... I'm feeling even thicker than usual.

Silence. Low priority I guess.

If I propose a patch that might get some response. /me threatens to post a 
patch.

Cheers,
Con