(tested on mainline but should apply to linux-next cleanly) ramzswap driver creates RAM based block devices which can be used (only) as swap disks. Pages swapped to these disks are compressed and stored in memory itself. However, these devices do not get any notification when a swap slot is freed (swap_map[i] reaches 0). So, we cannot free memory allocated corresponding to this swap slot. Such stale data can quickly accumulate in (compressed) memory defeating the whole purpose of such devices. To overcome this problem, we now add a callback in 'struct swap_info_struct' which is called as soon as a swap slot is freed. Adding handler for this callback: swapon notifier --> set_swap_free_notify(swap_type, fn) Removing handler: swapoff notifier --> set_swap_free_notify(swap_type, NULL) Alternative approaches: 1) Add callback directly in 'struct block_device_operations' but that is considered too hacky (nacked by Linus). 2) Use swap discard mechanism: It involves unncessary overhead of allocating 'discard bio' requests and its too slow to serve ramzswap needs. I also tried an approach similar to what Linus suggested: Create an address_space like swaper_space, so we can catch read/writes with a_ops->readpage() etc. However, this approach turned out to be quite difficult and I could not get it to work. Nitin Gupta (3): Add notifiers for swapon and swapoff events Send callback when a swap slot is freed ramzswap: Register for swap event notifiers and callback drivers/staging/ramzswap/TODO | 5 -- drivers/staging/ramzswap/ramzswap_drv.c | 79 ++++++++++++++++++++++++++++++- include/linux/swap.h | 15 ++++++ mm/swapfile.c | 70 +++++++++++++++++++++++++++ 4 files changed, 163 insertions(+), 6 deletions(-) delete mode 100644 drivers/staging/ramzswap/TODO _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
