Hi Ian, On Tue, Sep 01, 2015 at 08:22:04AM +0100, Ian Campbell wrote: > On Mon, 2015-08-31 at 16:46 +0200, Maxime Ripard wrote: > > When using fastboot and flashing a larger image such as the main partition > > of a system, the current 32MB limit for the buffer is quite small. > > (Apart from rooting/rescuing the odd phone I'm completely unfamiliar > with fastboot, so sorry if this is all obvious). > > The main partition of a system these days is measured in GB, I think. > So why does going from 32MB to 256MB for the buffer make a useful > difference? > > Is there some enormous per-buffer overhead which needs to be amortised? > Or is something else going on? > > IOW what is the practical impact of this change?
It really depends on the image content you're trying to flash, but there's two things to consider: - On a NAND device, you will just flash the actual content, but not the extra empty space in the partition, and the FS will automatically grow the first time you mount it. - If there's some blocks that are filled with the same content, the sparse image format I was refactoring earlier in that patchset will be able to compress it to 16 bytes (iirc), instead of a full block (512 bytes or a page, depending on whether you use an MMC or a NAND). On NAND images, there's often a lot of pages filled with 0xff, which fall into that category, I'd expect it to be similar on block partitions for the extra space. The current use case we have for example is to flash a 4GB partition with a debian system, in a UBI partition. Even though it's a decent system, storage size-wise, the file actually transfered and stored in the memory is around 210MB once compressed, and 270MB if not compressed. Of course, this will all depend on the ratio between the empty space and the files themselves, and what files you actually have there, but while 32MB is definitely useless, 256MB is already a decent size. Maxime -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com
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