Re: [patch] mm: pageable memory allocator (for DRM-GEM?)

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Tue, 23 Sep 2008 11:10:17 +0200
Nick Piggin <npiggin@suse.de> wrote:

> +void *pageable_vmap_object(pgobj_t *object, unsigned long start, unsigned long end)
> +{
> +	struct file *filp = (struct file *)object;
> +	struct address_space *mapping = filp->f_dentry->d_inode->i_mapping;
> +	unsigned int offset = start & ~PAGE_CACHE_MASK;
> +	pgoff_t first, last, i;
> +	struct page **pages;
> +	int nr;
> +	void *ret;
> +
> +	BUG_ON(start >= end);
> +
> +	first = start / PAGE_SIZE;
> +	last = DIV_ROUND_UP(end, PAGE_SIZE);
> +	nr = last - first;
> +
> +#ifndef CONFIG_HIGHMEM
> +	if (nr == 1) {
> +		struct page *page;
> +
> +		rcu_read_lock();
> +		page = radix_tree_lookup(&mapping->page_tree, first);
> +		rcu_read_unlock();
> +		BUG_ON(!page);
> +		BUG_ON(page_count(page) < 2);
> +
> +		ret = page_address(page);
> +
> +		goto out;
> +	}
> +#endif
> +
> +	pages = kmalloc(sizeof(struct page *) * nr, GFP_KERNEL);
> +	if (!pages)
> +		return NULL;
> +
> +	for (i = first; i < last; i++) {
> +		struct page *page;
> +
> +		rcu_read_lock();
> +		page = radix_tree_lookup(&mapping->page_tree, i);
> +		rcu_read_unlock();
> +		BUG_ON(!page);
> +		BUG_ON(page_count(page) < 2);
> +
> +		pages[i] = page;
> +	}
> +
> +	ret = vmap(pages, nr, VM_MAP, PAGE_KERNEL);
> +	kfree(pages);
> +	if (!ret)
> +		return NULL;
> +
> +out:
> +	return ret + offset;
> +}
> +
> +void pageable_vunmap_object(pgobj_t *object, void *ptr, unsigned long start, unsigned long end)
> +{
> +#ifndef CONFIG_HIGHMEM
> +	pgoff_t first, last;
> +	int nr;
> +
> +	BUG_ON(start >= end);
> +
> +	first = start / PAGE_SIZE;
> +	last = DIV_ROUND_UP(end, PAGE_SIZE);
> +	nr = last - first;
> +	if (nr == 1)
> +		return;
> +#endif
> +
> +	vunmap((void *)((unsigned long)ptr & PAGE_CACHE_MASK));
> +}
> +

Some questions..

 - could you use GFP_HIGHUSER rather than GFP_HIGHUSER_MOVABLE ?
   I think setting mapping_gfp_mask() (address_space->flags) to appropriate
   value is enough.

 - Can we mlock pages while it's vmapped ? (or Reserve and remove from LRU)
   Then, new split-lru can ignore these pages while there are mapped. over-killing ?

 - Doesn't we need to increase page->mapcount ?

 - memory resource contorller should account these pages ?
   (Maybe this is question to myself....)

Thanks,
-Kame