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SubjectRe: Prezeroing V3 [1/4]: Allow request for zeroed memory


On Mon, 10 Jan 2005, Christoph Lameter wrote:
>
> Yes. Right my ia64 centric vision got me again. Thanks for all the other
> patches that were posted. I hope this is now all cleared up?

Hmm.. I fixed things up, but I didn't exactly do it like the posted
patches.

Currently the BK tree
- doesn't use __GFP_ZERO with anonymous user-mapped pages (which is what
you wrote this whole thing for ;)

Potential fix: declare a per-architecture "alloc_user_highpage(vaddr)"
that does the proper magic on virtually indexed machines, and on others
it just does a "alloc_page(GFP_HIGHUSER | __GFP_ZERO)".

- verifies that nobody ever asks for a HIGHMEM allocation together with
__GFP_ZERO (nobody does - a quick grep shows that 99% of all uses are
statically clearly fine (there's a few HIGHMEM zero-page users, but
they are all GFP_KERNEL or similar), with just two special cases:

- get_zeroed_page() - which can't use HIGHMEM anyway
- shm.c does "mapping_gfp_mask(inode->i_mapping) | __GFP_ZERO"
and that's fine because while the mapping gfp masks may lack
GFP_FS and GFP_IO, they are always supposed to be ok with
waiting.

- moves "kernel_map_pages()" into "prep_new_page()" to fix the
DEBUG_PAGEALLOC issue (Chris Wright).

So that should take care of the known problems.

Linus
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