From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755116Ab0CEK1T (ORCPT ); Fri, 5 Mar 2010 05:27:19 -0500 Received: from mail-yw0-f184.google.com ([209.85.211.184]:49089 "EHLO mail-yw0-f184.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754881Ab0CEK1S (ORCPT ); Fri, 5 Mar 2010 05:27:18 -0500 X-Greylist: delayed 304 seconds by postgrey-1.27 at vger.kernel.org; Fri, 05 Mar 2010 05:27:18 EST MIME-Version: 1.0 Date: Fri, 5 Mar 2010 15:52:13 +0530 Message-ID: Subject: [PATCH 0/3] ramzswap: Eliminate stale data in compressed memory From: Nitin Gupta To: Hugh Dickins Cc: Linus Torvalds , Andrew Morton , Greg KH , Pekka Enberg , andi@firstfloor.org, linux-kernel Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 2) Use swap discard mechanism: It involves unncessary overhead of allocating 'discard bio' requests and its too slow to serve ramzswap needs. drivers/staging/ramzswap/ramzswap_drv.c | 91 +++++++++++++++++++++++++++++ drivers/staging/ramzswap/ramzswap_drv.h | 1 + drivers/staging/ramzswap/ramzswap_ioctl.h | 1 + include/linux/swap.h | 16 +++++- mm/swapfile.c | 78 ++++++++++++++++++++++++ 5 files changed, 185 insertions(+), 2 deletions(-)