From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx140.postini.com [74.125.245.140]) by kanga.kvack.org (Postfix) with SMTP id CB3B16B0002 for ; Mon, 4 Mar 2013 20:51:23 -0500 (EST) Received: by mail-wg0-f47.google.com with SMTP id dr13so4786986wgb.2 for ; Mon, 04 Mar 2013 17:51:22 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20130304150937.GB23767@cmpxchg.org> References: <20130304150937.GB23767@cmpxchg.org> Date: Tue, 5 Mar 2013 09:51:21 +0800 Message-ID: Subject: Re: [PATCH] mm: Fixup the condition whether the page cache is free From: Li Haifeng Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: "open list:MEMORY MANAGEMENT" , open list , linux-arm-kernel@lists.infradead.org Thanks very much for you explanation. :-) 2013/3/4 Johannes Weiner : > 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@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org