From: Miklos Szeredi Subject: Re: [PATCH 14/38] fallthru: ext2 fallthru support Date: Wed, 18 Aug 2010 10:26:26 +0200 Message-ID: References: <1276627208-17242-1-git-send-email-vaurora@redhat.com> <1276627208-17242-15-git-send-email-vaurora@redhat.com> <20100804230421.GC29353@shell> <20100817222731.GI5556@shell> Cc: miklos@szeredi.hu, jack@suse.cz, agruen@suse.de, viro@zeniv.linux.org.uk, jblunck@suse.de, hch@infradead.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, tytso@mit.edu, linux-ext4@vger.kernel.org To: Valerie Aurora Return-path: Received: from fxip-0047f.externet.hu ([88.209.222.127]:36551 "EHLO pomaz-ex.szeredi.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750859Ab0HRI0l (ORCPT ); Wed, 18 Aug 2010 04:26:41 -0400 In-reply-to: <20100817222731.GI5556@shell> (message from Valerie Aurora on Tue, 17 Aug 2010 18:27:32 -0400) Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, 17 Aug 2010, Valerie Aurora wrote: > > - hard links to make sure a separate inode is not necessary for each > > whiteout/fallthrough entry > > The problem with hard links is that you run into hard link limits. I > don't think we can do hard links for whiteouts and fallthrus. Each > whiteout or fallthru will cost an inode if we implement them as > extended attributes. This cost has to be balanced against the cost of > implementing them as dentries, which is mainly code complexity in > individual file systems. get_unlinked_inode() is a great idea. But I feel that individual inodes for each fallthrough is excessive. It'll make the first readdir() really really expensive and wastes a lot of disk and memory for no good reason. Not sure how to fix the hard link limits problem though... Thanks, Miklos