Re: [PATCH] General purpose zeroed page slab

Matthew Wilcox
2004-10-18T19:14:12Z

On Mon, Oct 18, 2004 at 12:03:04PM -0700, Luck, Tony wrote:
> >It's probably worth doing this with a static cachep in slab.c and only
> >exposing a get_zeroed_page() / free_zeroed_page() interface, with the
> >latter doing the memset to 0. I disagree with Andi over the dumbness
> >of zeroing the whole page. That makes it cache-hot, which is what you
> >want from a page you allocate from slab.
>
> We started this discussion with the plan of using this interface to
> allocate/free page tables at all levels in the page table hierarchy
> (rather than maintain a special purpose "quicklist" allocator for each
> level). This is a somewhat specialized usage in that we know that we
> have a completely zeroed page when we free ... so we really don't
> want the overhead of zeroing it again.

Ah, I'm not a VM weenie, so I didn't know this was guaranteed ;-)

> There is also somewhat limited
> benefit to the cache hotness argument here as most page tables (especially
> higher-order ones) are used very sparsely.
>
> That said, the idea to expose this slab only through a specific API
> should calm fears about accidental mis-use (with people freeing a page
> that isn't all zeroes).

So alloc_zeroed_page(), free_zeroed_page(), zero_and_free_page()
interfaces with a CONFIG option to check that the page passed to
free_zeroed_page() is already zero?

--
"Next the statesmen will invent cheap lies, putting the blame upon
the nation that is attacked, and every man will be glad of those
conscience-soothing falsities, and will diligently study them, and refuse
to examine any refutations of them; and thus he will by and by convince
himself that the war is just, and will thank God for the better sleep
he enjoys after this process of grotesque self-deception." -- Mark Twain