From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Mason Subject: Re: [PATCH] btrfs: call mark_inode_dirty when i_size is updated Date: Mon, 02 Feb 2009 20:04:52 -0500 Message-ID: <1233623092.20109.2.camel@think.oraclecorp.com> References: <6.0.0.20.2.20090202183710.06cdb8e0@172.19.0.2> <1233583946.18113.6.camel@think.oraclecorp.com> <6.0.0.20.2.20090203092917.06abcde0@172.19.0.2> Mime-Version: 1.0 Content-Type: text/plain Cc: linux-btrfs@vger.kernel.org To: Hisashi Hifumi Return-path: In-Reply-To: <6.0.0.20.2.20090203092917.06abcde0@172.19.0.2> List-ID: On Tue, 2009-02-03 at 09:36 +0900, Hisashi Hifumi wrote: > At 23:12 09/02/02, Chris Mason wrote: > >On Mon, 2009-02-02 at 20:00 +0900, Hisashi Hifumi wrote: > >> Hi Chris. > >> > >> I think it is needed to call mark_inode_dirty() when file size expands > >> in order to flush metadata updates to HDD through sync() syscall or > >> background_writeout(). > >> > > > >Thanks for reading through this code and sending the patch. > > > >I find the I_DIRTY flags one of the more confusing parts of the generic > >fs writeback cdoe. But, I think what happens is the > >btrfs_set_page_dirty function calls __set_page_dirty_nobuffers() which > >does: > > > >if (mapping->host) { > > /* !PageAnon && !swapper_space */ > > __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); > >} > > > >This should be enough to make sure the btrfs inodes are processed by > >background writeout and sync(). Please let me know if I'm misreading > >things. > > Surely, as you pointed out, btrfs_set_page_dirty calls > if (mapping->host) { > /* !PageAnon && !swapper_space */ > __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); > } > through _set_page_dirty_nobuffers. > But I_DIRTY_PAGES is not sufficient. > To flush metadata update to HDD through sync(), I_DIRTY_SYNC or > I_DIRTY_DATASYNC flag is needed. see __sync_single_inode. Since btrfs uses a dirty_inode callback, our inodes are never really dirty. The btree metadata always has the same information as the in-core inode does. The extra transaction commit steps taken at sync time are enough to get all the relevant metadata on disk. So, I think what happens is that I_DIRTY_PAGES is enough to get the data pages on disk and the transaction commit gets the metadata on disk. -chris