Messages in this thread | | | Date | Tue, 24 Apr 2007 14:24:11 -0700 | From | Andrew Morton <> | Subject | Re: Pagecache: find_or_create_page does not call a proper page allocator function |
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On Tue, 24 Apr 2007 13:58:35 -0700 (PDT) Christoph Lameter <clameter@sgi.com> wrote:
> On Tue, 24 Apr 2007, Andrew Morton wrote: > > > > Then I think we should disable page migration for allocations that do not > > > allow access to the policy zone. That would fix it. > > > > Can't we use mapping_gfp_mask() when allocating the destination page? > > There is no point in migrating something if you cannot reach the > destination. If the policy zone is not allowed by an allocation then the > page cannot be migrated because (on 32 bit NUMA) there is only a single > ZONE_NORMAL on the system. A different node requires a HIGHMEM allocation!
don't care really. If we're allocating a page for an address_space, we should be using its allocation mask. As I said, we might add more things in the future.
If in so doing the user pointlessly wastes some CPU cycles in one weird case, it doesn't matter a lot.
> > It would be better to do so, really. Who knows, mapping_gfp_mask() might > > be extented in the future to say "I want GFP_NOIO" or something. Or a > > filesystem might specify GFP_KERNEL for regular pagecache pages or > > whatever. > > Hmmm..... How about a VM_DONTMIGRATE flag instead? That would be easy to > check and could be set by a device that must have all pages of the address > space conforming to the gfp mask. > > Or more general > > VM_STRICT_ALLOC?
ug. That's special-casing the blockdev pagecache peculiarity when someone mmaps it. It'd be better to stick with the existing interfaces and conventions: the address_space gets to dictate how is pages are allocated.
> > Generally, the interface is "address_space tells core kernel how to > > allocate its pages", and to be nice we should honour that in all places > > where we allocate a page for an address_space. > > > > If we'd had any brains we would have implemented this function as an > > address_space_operations callback, but we don't so we didn't. > > We have enough flags I think.
mapping_gfp_mask if a pretty foul thing. Adding
struct page (*alloc_page)(struct address_space *mapping);
to address_space_operations would be a quite nice cleanup.
But I ain't taking cleanups at present.
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