Hi all.
As we all know, pageflags have been a scarce resource for a while now. These
patches seek to help address that issue by adding support for a new type
of 'dynamically allocated' pageflag.
The basic idea is that we use per node & zone bitmaps built out of order zero
allocations, to replace bits in page->flags. Bitmaps can be sparse, being
populated when a bit on the page is set, and returning zero for all bits in
sparse pages. Untested hotplug support is included.
This method of storing the data does of course come with a performance hit.
I've included some simple timing loops in #ifdef'd code that help quantify
that.
Interestingly, the new implementation is actually quicker under some
circumstances. In cases where the usage pattern involves operating on the
flags for a number of pages in succession, the hit involved in getting the
struct pages from main memory appears to be greater than that involved in
calculating which unsigned long and bit to test.
Tested only on UP (x86_64) so far.
Regards,
Nigel
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