Thanks very much for you explanation. :-) 2013/3/4 Johannes Weiner <hannes@xxxxxxxxxxx>: > On Mon, Mar 04, 2013 at 09:54:26AM +0800, Li Haifeng wrote: >> When a page cache is to reclaim, we should to decide whether the page >> cache is free. >> IMO, the condition whether a page cache is free should be 3 in page >> frame reclaiming. The reason lists as below. >> >> When page is allocated, the page->_count is 1(code fragment is code-1 ). >> And when the page is allocated for reading files from extern disk, the >> page->_count will increment 1 by page_cache_get() in >> add_to_page_cache_locked()(code fragment is code-2). When the page is to >> reclaim, the isolated LRU list also increase the page->_count(code >> fragment is code-3). > > The page count is initialized to 1, but that does not stay with the > object. It's a reference that is passed to the allocating task, which > drops it again when it's done with the page. I.e. the pattern is like > this: > > instantiation: > page = page_cache_alloc() /* instantiator reference -> 1 */ > add_to_page_cache(page, mapping, offset) > get_page(page) /* page cache reference -> 2 */ > lru_cache_add(page) > get_page(page) /* pagevec reference -> 3 */ > /* ...initiate read, write, associate buffers, ... */ > page_cache_release(page) /* drop instantiator reference -> 2 + private */ > > reclaim: > lru_add_drain() > page_cache_release(page) /* drop pagevec reference -> 1 + private */ > __isolate_lru_page(page) > page_cache_get(page) /* reclaim reference -> 2 + private */ > is_page_cache_freeable(page) > try_to_free_buffers() /* drop buffer ref -> 2 */ > __remove_mapping() /* drop page cache and isolator ref -> 0 */ > free_hot_cold_page() -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>