From mboxrd@z Thu Jan 1 00:00:00 1970 From: Edward Shishkin Subject: Re: reiser4 mkfs, cryptcompress, tail packing, etc. Date: Tue, 24 Aug 2010 19:47:59 +0200 Message-ID: <4C7405CF.3040609@gmail.com> References: <4C73EDEF.8020701@bobich.net> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4C73EDEF.8020701@bobich.net> Sender: reiserfs-devel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Gordan Bobic Cc: reiserfs-devel@vger.kernel.org Gordan Bobic wrote: > Hi, Hello. > > It's been a while since I last tried reiser4, and having just looked > at the wiki, I couldn't find any info at all on the cryptocompress > plugin and tail packing options at mkfs time specifically relating to > reiser4. mkfs.reiser4 -l: compression modes (works "per file"): "latt" (id:0x1 type:0xd) ['Check on dynamic lattice' compression mode plugin.] If logical cluster in incompressible, then switch compression off and check every K-th cluster, where K dynamically increased to 32 on every non-success after compression. If cluster is compressible, than K is set back to 1, etc.. "ultim" (id:0x2 type:0xd) ['Check ultimately' compression mode plugin.] Switch compression off forever after the first case of non-success. "force" (id:0x3 type:0xd) ['Compress evrything' compression mode plugin.] Force to compress everything. "conv" (id:0x4 type:0xd) ['Convert to extent' compression mode plugin.] If the first logical cluster of the file is incompressible, then switch compression off forever. This is default mode, but it works not good on various media-files.. > Also, is there a nolog option on reiser4 as there is on reiserfs? no sorry, currently reiser4 transaction manager can not be switched off. > > The reason I ask is because I am looking for a file system that > improves on ext2 for very slow writing flash media (think cheap USB > sticks, SD cards, etc.). So, ideally, I want to disable journalling > and enable compression, to minimize the number of writing to the > underlying media. In theory, compression with journalling switched off > should give reiser4 an edge in this use-case, so I just wanted to > check what the current state of the compression is (couldn't find any > references to -o create=ccreg40 in the wiki), and that it works as one > might expect (compressing before committing to disk). Works stable as expected (i.e. compression "on commits") > > > Another question (not sure if it is specifically related to reiser4 or > generic) is about compressed hard-linked DLLs and mmap. Specifically, > if a .so is hard-linked in two places, dynamically linking to each > instance causes both to be mmapped to the same memory since they'll > have the same inode, and that means the memory is only used once. How > does this work if the .so is compressed? Does it all still work the > same, with the decompressed file being in a single mmap for both > dynamically linked instances? Works as usual: when populating address space by readpage(s) data are read from disk and decompressed. If page gets dirty, then its data will be compressed in flush time and written to disk. > > Many thanks. You are welcome, Edward.