Re: [PATCH][RFC] 4K stacks default, not a debug thing any more...?

Rene Herman
2007-07-18T17:18:40Z

On 07/18/2007 06:54 PM, Matt Mackall wrote:

> You can expect the distribution of file sizes to follow a gamma
> distribution, with a large hump towards the small end of the spectrum
> around 1-10K, dropping off very rapidly as file sizes grow.

Okay.

>> Not too sure then that 8K wouldn't be something I'd want, given fewer
>> pagefaults and all that...
>
> Fewer minor pagefaults, perhaps. Readahead already deals with most of
> the major pagefaults that larger pages would.

Mmm, yes.

> Anyway, raising the systemwide memory overhead by up to 15% seems an
> awfully silly way to address the problem of not being able to allocate a
> stack when you're down to your last 1 or 2% of memory!

Well, I've seen larger pagesizes submerge in more situations, specifically
in allocation overhead -- ie, making the struct page's fit in lowmem for
hugemem x86 boxes was the first I heard of it. But yes, otherwise (also)
mostly database loads which obviously have moved to 64-bit since.

Pagecache tail-packing seems like a promising idea to deal with the downside
of larger pages but I'll admit I'm not particularly sure how many _up_ sides
to them are left on x86 (not -64) now that's becoming a legacy architecture
(and since you just shot down the pagefaults thing).

Rene.