On Tue, Oct 23, 2012 at 08:46:51PM +0800, Ying Zhu wrote: > Hi, > Recently we ran into the bug that an opened file's ra_pages does not > synchronize with it's backing device's when the latter is changed > with blockdev --setra, the application needs to reopen the file > to know the change, or simply call fadvise(fd, POSIX_FADV_NORMAL) to reset the readhead window to the (new) bdi default. > which is inappropriate under our circumstances. Which are? We don't know your circumstances, so you need to tell us why you need this and why existing methods of handling such changes are insufficient... Optimal readahead windows tend to be a physical property of the storage and that does not tend to change dynamically. Hence block device readahead should only need to be set up once, and generally that can be done before the filesystem is mounted and files are opened (e.g. via udev rules). Hence you need to explain why you need to change the default block device readahead on the fly, and why fadvise(POSIX_FADV_NORMAL) is "inappropriate" to set readahead windows to the new defaults. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>