From mboxrd@z Thu Jan 1 00:00:00 1970 From: "junjie cai" Subject: Re: Linux page cache issue? Date: Wed, 28 Mar 2007 16:35:25 +0900 Message-ID: References: <4ae3c140703272345y3b3cb3cexf4c4b63e0035d5b9@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-kernel , linux-fsdevel To: "Xin Zhao" Return-path: Received: from ug-out-1314.google.com ([66.249.92.175]:21456 "EHLO ug-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753077AbXC1Hf2 (ORCPT ); Wed, 28 Mar 2007 03:35:28 -0400 Received: by ug-out-1314.google.com with SMTP id 44so125869uga for ; Wed, 28 Mar 2007 00:35:26 -0700 (PDT) In-Reply-To: <4ae3c140703272345y3b3cb3cexf4c4b63e0035d5b9@mail.gmail.com> Content-Disposition: inline Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Hi, generic_forget_inode() don't call trancate_inode_pages() if FS is still active see the 10449 line below: 1040 static void generic_forget_inode(struct inode *inode) 1041 { 1042 struct super_block *sb = inode->i_sb; 1043 1044 if (!hlist_unhashed(&inode->i_hash)) { 1045 if (!(inode->i_state & (I_DIRTY|I_LOCK))) 1046 list_move(&inode->i_list, &inode_unused); 1047 inodes_stat.nr_unused++; 1048 spin_unlock(&inode_lock); 1049 if (!sb || (sb->s_flags & MS_ACTIVE)) 1050 return; 1051 write_inode_now(inode, 1); 1052 spin_lock(&inode_lock); 1053 inodes_stat.nr_unused--; 1054 hlist_del_init(&inode->i_hash); 1055 } 1056 list_del_init(&inode->i_list); 1057 list_del_init(&inode->i_sb_list); 1058 inode->i_state|=I_FREEING; 1059 inodes_stat.nr_inodes--; 1060 spin_unlock(&inode_lock); 1061 if (inode->i_data.nrpages) 1062 truncate_inode_pages(&inode->i_data, 0); 1063 clear_inode(inode); 1064 destroy_inode(inode); 1065 On 3/28/07, Xin Zhao wrote: > Hi, > > If a Linux process opens and reads a file A, then it closes the file. > Will Linux keep the file A's data in cache for a while in case another > process opens and reads the same in a short time? I think that is what > I heard before. > > But after I digged into the kernel code, I am confused. > > When a process closes the file A, iput() will be called, which in turn > calls the follows two functions: > iput_final()->generic_drop_inode() > > But from the following calling chain, we can see that file close will > eventually lead to evict and free all cached pages. Actually in > truncate_complete_page(), the pages will be freed. This seems to > imply that Linux has to re-read the same data from disk even if > another process B read the same file right after process A closes the > file. That does not make sense to me. > > /***calling chain ***/ > generic_delete_inode/generic_forget_inode()-> > truncate_inode_pages()->truncate_inode_pages_range()-> > truncate_complete_page()->remove_from_page_cache()-> > __remove_from_page_cache()->radix_tree_delete() > > Am I missing something? Can someone please provide some advise? > > Thanks a lot > -x > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >