Hi Tim,
On Mon, Sep 10, 2012 at 09:19:25AM -0700, Tim Chen wrote:
> We gather the pages that need to be unmapped in shrink_page_list. We batch
> the unmap to reduce the frequency of acquisition of
> the tree lock protecting the mapping's radix tree. This is
> possible as successive pages likely share the same mapping in
> __remove_mapping_batch routine. This avoids excessive cache bouncing of
> the tree lock when page reclamations are occurring simultaneously.
>
> Tim
> ---
> Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> ---
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index aac5672..d4ab646 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -600,6 +600,85 @@ cannot_free:
> return 0;
> }
>
> +/* Same as __remove_mapping, but batching operations to minimize locking */
> +/* Pages to be unmapped should be locked first */
Use below comment style.
/*
* blah, blah,
*/
> +static int __remove_mapping_batch(struct list_head *unmap_pages,
> + struct list_head *ret_pages,
> + struct list_head *free_pages)
> +{
> + struct address_space *mapping, *next;
> + LIST_HEAD(swap_pages);
> + swp_entry_t swap;
> + struct page *page;
> + int nr_reclaimed;
Use unsigned long instead of int.
> +
> + mapping = NULL;
> + nr_reclaimed = 0;
> + while (!list_empty(unmap_pages)) {
> +
> + page = lru_to_page(unmap_pages);
> + BUG_ON(!PageLocked(page));
> +
> + list_del(&page->lru);
> + next = page_mapping(page);
> + if (mapping != next) {
> + if (mapping)
> + spin_unlock_irq(&mapping->tree_lock);
> + mapping = next;
> + spin_lock_irq(&mapping->tree_lock);
> + }
> +
> + if (!page_freeze_refs(page, 2))
> + goto cannot_free;
> + if (unlikely(PageDirty(page))) {
> + page_unfreeze_refs(page, 2);
> + goto cannot_free;
> + }
> +
> + if (PageSwapCache(page)) {
> + __delete_from_swap_cache(page);
> + /* swapcache_free need to be called without tree_lock */
> + list_add(&page->lru, &swap_pages);
> + } else {
> + void (*freepage)(struct page *);
> +
> + freepage = mapping->a_ops->freepage;
> +
> + __delete_from_page_cache(page);
> + mem_cgroup_uncharge_cache_page(page);
> +
> + if (freepage != NULL)
> + freepage(page);
> +
> + unlock_page(page);
If you use unlock_page, you removes a978d6f5.
You can use __clear_page_locked.
> + nr_reclaimed++;
> + list_add(&page->lru, free_pages);
> + }
> + continue;
> +cannot_free:
> + unlock_page(page);
> + list_add(&page->lru, ret_pages);
> + VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
> +
> + }
> +
> + if (mapping)
> + spin_unlock_irq(&mapping->tree_lock);
> +
> + while (!list_empty(&swap_pages)) {
> + page = lru_to_page(&swap_pages);
> + list_del(&page->lru);
> +
> + swap.val = page_private(page);
> + swapcache_free(swap, page);
> +
> + unlock_page(page);
Ditto.
> + nr_reclaimed++;
> + list_add(&page->lru, free_pages);
> + }
> +
> + return nr_reclaimed;
> +}
> /*
> * Attempt to detach a locked page from its ->mapping. If it is dirty or if
> * someone else has a ref on the page, abort and return 0. If it was
> @@ -771,6 +850,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> {
> LIST_HEAD(ret_pages);
> LIST_HEAD(free_pages);
> + LIST_HEAD(unmap_pages);
> int pgactivate = 0;
> unsigned long nr_dirty = 0;
> unsigned long nr_congested = 0;
> @@ -969,17 +1049,13 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> }
> }
>
> - if (!mapping || !__remove_mapping(mapping, page))
> + if (!mapping)
> goto keep_locked;
>
> - /*
> - * At this point, we have no other references and there is
> - * no way to pick any more up (removed from LRU, removed
> - * from pagecache). Can use non-atomic bitops now (and
> - * we obviously don't have to worry about waking up a process
> - * waiting on the page lock, because there are no references.
> - */
Please don't remove this description and move it into your function with
__clear_page_locked.
> - __clear_page_locked(page);
> + /* remove pages from mapping in batch at end of loop */
> + list_add(&page->lru, &unmap_pages);
> + continue;
> +
> free_it:
> nr_reclaimed++;
>
> @@ -1014,6 +1090,9 @@ keep_lumpy:
> VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
> }
>
> + nr_reclaimed += __remove_mapping_batch(&unmap_pages, &ret_pages,
> + &free_pages);
> +
> /*
> * Tag a zone as congested if all the dirty pages encountered were
> * backed by a congested BDI. In this case, reclaimers should just
--
Kind regards,
Minchan Kim
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