From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx190.postini.com [74.125.245.190]) by kanga.kvack.org (Postfix) with SMTP id 3E80D6B0002 for ; Sun, 3 Mar 2013 20:54:28 -0500 (EST) Received: by mail-we0-f175.google.com with SMTP id x8so4078437wey.6 for ; Sun, 03 Mar 2013 17:54:26 -0800 (PST) MIME-Version: 1.0 Date: Mon, 4 Mar 2013 09:54:26 +0800 Message-ID: Subject: [PATCH] mm: Fixup the condition whether the page cache is free From: Li Haifeng Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: "open list:MEMORY MANAGEMENT" , open list , linux-arm-kernel@lists.infradead.org, Johannes Weiner 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). According above reasons, when the file page is freeable, the page->_count should be 3 instead of 2. buffered_rmqueue ->prep_new_page->set_page_refcounted: 24 /* 25 * Turn a non-refcounted page (->_count =3D=3D 0) into refcounted with 26 * a count of one. 27 */ 28 static inline void set_page_refcounted(struct page *page) 29 { 30 VM_BUG_ON(PageTail(page)); 31 VM_BUG_ON(atomic_read(&page->_count)); 32 set_page_count(page, 1); 33 } do_generic_file_read ->add_to_page_cache_lru-> add_to_page_cache-> add_to_page_cache_locked: int add_to_page_cache_locked(struct page *page, struct address_space *mapping, pgoff_t offset, gfp_t gfp_mask) { =85 page_cache_get(page); page->mapping =3D mapping; page->index =3D offset; spin_lock_irq(&mapping->tree_lock); error =3D radix_tree_insert(&mapping->page_tree, offset, page); if (likely(!error)) { mapping->nrpages++; __inc_zone_page_state(page, NR_FILE_PAGES); spin_unlock_irq(&mapping->tree_lock); =85 } static noinline_for_stack unsigned long shrink_inactive_list(unsigned long nr_to_scan, struct mem_cgroup_zone *mz, struct scan_control *sc, int priority, int file) { =85 nr_taken =3D isolate_lru_pages(nr_to_scan, mz, &page_list, &nr_scanned, sc, isolate_mode, 0, file); =85 nr_reclaimed =3D shrink_page_list(&page_list, mz, sc, priority, &nr_dirty, &nr_writeback); } Remarks for code-3: isolate_lru_pages() will call get_page_unless_zero() ultimately to increase the page->_count by 1. And shrink_page_list() will call is_page_cache_freeable() finally to check whether the page cache is free.