Re: [PATCHv3 14/41] filemap: allocate huge page in page_cache_read(), if allowed

Jan Kara
2016-10-11T16:15:45Z

On Thu 15-09-16 14:54:56, Kirill A. Shutemov wrote:
> This patch adds basic functionality to put huge page into page cache.
>
> At the moment we only put huge pages into radix-tree if the range covered
> by the huge page is empty.
>
> We ignore shadow entires for now, just remove them from the tree before
> inserting huge page.
>
> Later we can add logic to accumulate information from shadow entires to
> return to caller (average eviction time?).
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
> include/linux/fs.h | 5 ++
> include/linux/pagemap.h | 21 ++++++-
> mm/filemap.c | 148 +++++++++++++++++++++++++++++++++++++++++++-----
> 3 files changed, 157 insertions(+), 17 deletions(-)
>
...
> @@ -663,16 +663,55 @@ static int __add_to_page_cache_locked(struct page *page,
> page->index = offset;
>
> spin_lock_irq(&mapping->tree_lock);
> - error = page_cache_tree_insert(mapping, page, shadowp);
> + if (PageTransHuge(page)) {
> + struct radix_tree_iter iter;
> + void **slot;
> + void *p;
> +
> + error = 0;
> +
> + /* Wipe shadow entires */
> + radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, offset) {
> + if (iter.index >= offset + HPAGE_PMD_NR)
> + break;
> +
> + p = radix_tree_deref_slot_protected(slot,
> + &mapping->tree_lock);
> + if (!p)
> + continue;
> +
> + if (!radix_tree_exception(p)) {
> + error = -EEXIST;
> + break;
> + }
> +
> + mapping->nrexceptional--;
> + rcu_assign_pointer(*slot, NULL);

I think you also need something like workingset_node_shadows_dec(node)
here. It would be even better if you used something like
clear_exceptional_entry() to have the logic in one place (you obviously
need to factor out only part of clear_exceptional_entry() first).

> + }
> +
> + if (!error)
> + error = __radix_tree_insert(&mapping->page_tree, offset,
> + compound_order(page), page);
> +
> + if (!error) {
> + count_vm_event(THP_FILE_ALLOC);
> + mapping->nrpages += HPAGE_PMD_NR;
> + *shadowp = NULL;
> + __inc_node_page_state(page, NR_FILE_THPS);
> + }
> + } else {
> + error = page_cache_tree_insert(mapping, page, shadowp);
> + }

And I'd prefer to have this logic moved to page_cache_tree_insert() because
logically it IMHO belongs there - it is a simply another case of handling
of radix tree used for page cache.

Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR