On Fri, 28 Jan 2011, Marek Szyprowski wrote: > This commit add code that flushed page cache disk buffers every 128 read > and write request. It has almost no impact on the performance of the > emulate usb drive but saves system page cache from being filled with > useless emulated disk data. > > Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> > Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx> > > --- > > Hello, > > In the embedded system development we encoutered a really anoying > behaviour of USB mass storage gadget. We use it to export SD card as USB > disk. However when user copies a lot of data from or to the USB disk, > the mass storage gadget consumes almost all pages from system page > cache. This results in a significant degradation of system and io > performance. A lot of valid and really often used disk cache data is > wiped from memory and need to be constantly reloaded. > > Caching mass storage backing file is usually useless. Host system very > rarely sends requests for the same blocks in the limited time window. > Usually there is another caching layer on the host system anyway. > > Disabling page cache for the backing file is also not the solution, > because mmc perform really bad on direct 512 byte reads and writes. > > I've did a quick hack to limit the amount of page cache that is being > used by mass storage gadget. I've forced mass storage gadget to flush > and invalidate page cache once every 128 read or write request. I know > that the patch is ugly but it solves the issue. Can you post an equivalent patch for file_storage.c? The same issues apply there. > Do you have any suggestion how to correctly introduce a method of > limiting page cache usage in the mass storage gadget? How do other storage or filesystem servers do it (e.g., NFS, CIFS)? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
