This all seems quite complicated.
I think the interface we'd want is more one that has a little
cache of a single page in the queue, and a little bitmap which
sub-page size blocks of it are used.
Something like (pseudo code minus locking):
void *blk_alloc_sector_buffer(struct block_device *bdev, gfp_t gfp)
{
unsigned block_size = block_size(bdev);
if (blocksize >= PAGE_SIZE)
return (void *)__get_free_pages(gfp, get_order(blocksize));
if (bdev->fragment_cache_page) {
[ <find fragment in bdev->fragment_cache_page using
e.g. bitmap and return if found]
}
bdev->fragment_cache_page = (void *)__get_free_page(gfp);
goto find_again;
}
note that the locking also is important, preferably we'd be able to do
something lockless.
