From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 21 Sep 2007 13:48:28 +0200 From: Peter Zijlstra Subject: Re: [RFC][PATCH] page->mapping clarification [1/3] base functions Message-ID: <20070921134828.45ca967e@twins> In-Reply-To: <20070919164308.281f9960.kamezawa.hiroyu@jp.fujitsu.com> References: <20070919164308.281f9960.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: KAMEZAWA Hiroyuki Cc: LKML , "linux-mm@kvack.org" , Andrew Morton , "nickpiggin@yahoo.com.au" , ricknu-0@student.ltu.se List-ID: On Wed, 19 Sep 2007 16:43:08 +0900 KAMEZAWA Hiroyuki wrote: > A clarification of page <-> fs interface (page cache). > > At first, each FS has to access to struct page->mapping directly. > But it's not just pointer. (we use special 1bit enconding for anon.) > > Although there is historical consensus that page->mapping points to its inode's > address space, I think adding some neat helper functon is not bad. > > This patch adds page-cache.h which containes page<->address_space<->inode > function which is required (used) by subsystems. > > Following functions are added > > * page_mapping_cache() ... returns address space if a page is page cache > * page_mapping_anon() ... returns anon_vma if a page is anonymous page. > * page_is_pagecache() ... returns true if a page is page-cache. > * page_inode() ... returns inode which a page-cache belongs to. > * is_page_consistent() ... returns true if a page is still valid page cache > > Followings are moved > * page_mapping() ... returns swapper_space or address_space a page is on. > (from mm.h) > * page_index() ... returns position of a page in its inode > (from mm.h) > * remove_mapping() ... a safe routine to remove page->mapping from page. > (from swap.h) I have two other functions that might want integration with this scheme: page_file_mapping() ... returns backing address space page_file_index() ... returns the index therein They are identical to page_mapping_cache() and page_index() for page cache pages, but they also work on swap cache pages. That is, for swapcache pages they return: page_file_mapping: page_swap_info(page)->swap_file->f_mapping page_file_index: swp_offset((swp_offset_t)page_private(page)) When a filesystem uses these functions instead of page->mapping and page->index, it allows passing swap cache pages into the regular filesystem read/write paths. This is useful for things like swap over NFS, where swap is backed by a swapfile on a 'regular' filesystem. -- 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