From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from szxga01-in.huawei.com ([119.145.14.64]:60458 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755467Ab2ICBX0 (ORCPT ); Sun, 2 Sep 2012 21:23:26 -0400 Message-ID: <5044067E.7000607@huawei.com> Date: Mon, 3 Sep 2012 09:23:10 +0800 From: Li Zefan MIME-Version: 1.0 To: CC: Ben Wreder , Subject: Re: Tail packing References: <20120902052537.GF17430@twin.jikos.cz> In-Reply-To: <20120902052537.GF17430@twin.jikos.cz> Content-Type: text/plain; charset="ISO-8859-1" Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 2012/9/2 13:25, David Sterba wrote: > On Fri, Aug 31, 2012 at 04:40:36PM +0200, Ben Wreder wrote: >> The disk format description implies that btrfs should be able to >> support tail packing. I just did some experimentation, and while small >> files are packed, it seems that files occupying more than one block >> are not. For example, a lot of 32769-byte files will end up taking >> over 36KB on average (a small excess due to the metadata itself). >> >> So just to confirm - btrfs does not currently support tail-packing, is that correct? > > Currently it's not the reiserfs-style tail packing. The feature is > advertised as "Space-efficient packing of small files", as Josef > replied, if a file fits into a leaf block, it's stored into the metadata > blocks. The limit is 3916 bytes for 4k blocks, without compression. If > compression is on, the 'small file' size limit is even higher for > moderately compressible files. If the actual size of the file is > 3916 bytes, no matter how compressible it is, it won't be inlined. > An example where this could apply is a > maildir, and IIRC this was why reiserfs was chosen on mail servers. >