Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754694AbXJOI3H (ORCPT ); Mon, 15 Oct 2007 04:29:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754783AbXJOI2y (ORCPT ); Mon, 15 Oct 2007 04:28:54 -0400 Received: from mtagate1.uk.ibm.com ([195.212.29.134]:2455 "EHLO mtagate1.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753741AbXJOI2w (ORCPT ); Mon, 15 Oct 2007 04:28:52 -0400 From: Christian Borntraeger To: Andrew Morton Subject: [PATCH resend] ramdisk: fix zeroed ramdisk pages on memory pressure User-Agent: KMail/1.9.7 Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Martin Schwidefsky , "Theodore Ts'o" MIME-Version: 1.0 Content-Disposition: inline Date: Mon, 15 Oct 2007 10:28:34 +0200 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <200710151028.34407.borntraeger@de.ibm.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2871 Lines: 73 Andrew, this is a resend of a bugfix patch. Ramdisk seems a bit unmaintained, so decided to sent the patch to you :-). I have CCed Ted, who did work on the code in the 90s. I found no current email address of Chad Page. We have seen ramdisk based install systems, where some pages of mapped libraries and programs were suddendly zeroed under memory pressure. This should not happen, as the ramdisk avoids freeing its pages by keeping them dirty all the time. It turns out that there is a case, where the VM makes a ramdisk page clean, without telling the ramdisk driver. On memory pressure shrink_zone runs and it starts to run shrink_active_list. There is a check for buffer_heads_over_limit, and if true, pagevec_strip is called. pagevec_strip calls try_to_release_page. If the mapping has no releasepage callback, try_to_free_buffers is called. try_to_free_buffers has now a special logic for some file systems to make a dirty page clean, if all buffers are clean. Thats what happened in our test case. The solution is to provide a noop-releasepage callback for the ramdisk driver. This avoids try_to_free_buffers for ramdisk pages. To trigger the problem, you have to make buffer_heads_over_limit true, which means: - lower max_buffer_heads or - have a system with lots of high memory Andrew, if there are no objections - please apply. The patch applies against todays git. Signed-off-by: Christian Borntraeger --- drivers/block/rd.c | 13 +++++++++++++ 1 files changed, 13 insertions(+) Index: linux-2.6/drivers/block/rd.c =================================================================== --- linux-2.6.orig/drivers/block/rd.c +++ linux-2.6/drivers/block/rd.c @@ -189,6 +189,18 @@ static int ramdisk_set_page_dirty(struct return 0; } +/* + * releasepage is called by pagevec_strip/try_to_release_page if + * buffers_heads_over_limit is true. Without a releasepage function + * try_to_free_buffers is called instead. That can unset the dirty + * bit of our ram disk pages, which will be eventually freed, even + * if the page is still in use. + */ +static int ramdisk_releasepage(struct page *page, gfp_t dummy) +{ + return 0; +} + static const struct address_space_operations ramdisk_aops = { .readpage = ramdisk_readpage, .prepare_write = ramdisk_prepare_write, @@ -196,6 +208,7 @@ static const struct address_space_operat .writepage = ramdisk_writepage, .set_page_dirty = ramdisk_set_page_dirty, .writepages = ramdisk_writepages, + .releasepage = ramdisk_releasepage, }; static int rd_blkdev_pagecache_IO(int rw, struct bio_vec *vec, sector_t sector, - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/