On Wed 2009-06-24 18:49:11, Marco wrote: > >> Pavel Machek wrote: > >>> On Mon 2009-06-22 14:50:01, Tim Bird wrote: > >>>> Pavel Machek wrote: > >>>>>> block of fast non-volatile RAM that need to access data on it using a > >>>>>> standard filesytem interface." > >>>>> Turns a block of fast RAM into 13MB/sec disk. Hmm. I believe you are > >>>>> better with ext2. > >>>> Not if you want the RAM-based filesystem to persist over a kernel > >>>> invocation. > >>> Yes, you'll need to code Persistent, RAM-based _block_device_. > >> First of all I have to say that I'd like to update the site and make it > >> clearer but at the moment it's not possible because I'm not the admin > >> and I've already asked to the sourceforge support to have this possibility. > >> > >> About the comments: sincerely I don't understand the comments. We have > >> *already* a fs that takes care to remap a piace of ram (ram, sram, > >> nvram, etc.), takes care of caching problems, takes care of write > > > > Well, it looks pramfs design is confused. 13MB/sec shows that caching > > _is_ useful for pramfs. So...? > > caching problems means to avoid filesystem corruption, so dirty pages in > the page cache are not allowed to be written back to the backing-store > RAM. It's clear that there is a performance penalty. This penalty should > be reduced by the access speed of the RAM, however the performance are > not important for this special fs as Tim Bird said, so this question is > not relevant for me. If this issue is not clear enough on the web site, > I hope I can update the information in the future. Yes, please update the pages... > >> You are talked about journaling. This schema works well for a disk, but > >> what about a piece of ram? What about a crazy kernel that write in that > >> area for a bug? Do you remember for example the e1000e bug? It's not > > > > I believe you need both journaling *and* write protection. How do you > > handle power fault while writing data? > > Ah now the write protection is a "needed feature", in your previous > comment you talked about why not use ext2/3....... write protection should be handled at block device layer, not filesystem layer. So yes, use ext2. You still did not explain how you avoid the need for journalling... Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
