Re: [RFC][PATCH 3/4] filemap: implement filemap allocate post callback for page_owner

[Matthew Wilcox <willy@infradead.org>]

On Thu, Nov 09, 2023 at 11:25:20AM +0800, Jeff Xie wrote:
> +static int filemap_alloc_post_page_owner(struct folio *folio, struct task_struct *tsk,
> +			void *data, char *kbuf, size_t count)
> +{
> +	int ret;
> +	int mapcount;
> +	dev_t s_dev;
> +	struct inode *inode;
> +	struct vm_area_struct *vma;
> +	struct mm_struct *mm;
> +	unsigned long virtual_start = 0x0;
> +	unsigned long virtual_end = 0x0;
> +	struct address_space *mapping = data;

This is just folio->mapping.

> +	mapcount = folio_mapcount(folio);
> +	if (mapcount && tsk && tsk->mm) {
> +		mm = tsk->mm;
> +		VMA_ITERATOR(vmi, mm, 0);
> +		mmap_read_lock(mm);
> +		for_each_vma(vmi, vma) {
> +			if (page_mapped_in_vma(&folio->page, vma)) {
> +				virtual_start = vma_address(&folio->page, vma);
> +				virtual_end = virtual_start + folio_nr_pages(folio) * PAGE_SIZE;
> +				break;
> +			}
> +		}
> +		mmap_read_unlock(mm);
> +	}

Why not just walk the rmap directly to find out where it's mapped in
any process instead of the one which allocated it?