From: Mingming Cao Subject: ext2: Fix ext2 block reservation early ENOSPC issue Date: Thu, 28 Aug 2008 16:05:08 -0700 Message-ID: <1219964708.6384.73.camel@mingming-laptop> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Andrew Morton , tytso To: linux-ext4@vger.kernel.org Return-path: Received: from e2.ny.us.ibm.com ([32.97.182.142]:54908 "EHLO e2.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755308AbYH1XFJ (ORCPT ); Thu, 28 Aug 2008 19:05:09 -0400 Received: from d01relay02.pok.ibm.com (d01relay02.pok.ibm.com [9.56.227.234]) by e2.ny.us.ibm.com (8.13.8/8.13.8) with ESMTP id m7SN58VZ013259 for ; Thu, 28 Aug 2008 19:05:08 -0400 Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by d01relay02.pok.ibm.com (8.13.8/8.13.8/NCO v9.0) with ESMTP id m7SN58fp174436 for ; Thu, 28 Aug 2008 19:05:08 -0400 Received: from d01av02.pok.ibm.com (loopback [127.0.0.1]) by d01av02.pok.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id m7SN58mV018567 for ; Thu, 28 Aug 2008 19:05:08 -0400 Sender: linux-ext4-owner@vger.kernel.org List-ID: From: Mingming Cao ext2: Fix ext2 nomballoc allocator for ENOSPC We could run into ENOSPC error on ext2, even when there is free blocks on the filesystem. The problem is triggered in the case the goal block group has 0 free blocks , and the rest block groups are skipped due to the check of "free_blocks < windowsz/2". Current code could fall back to non reservation allocation to prevent early ENOSPC after examing all the block groups with reservation on , but this code was bypassed if the reservation window is turned off already, which is true in this case. This patch fixed two issues: 1) We don't need to turn off block reservation if the goal block group has 0 free blocks left and continue search for the rest of block groups. Current code the intention is to turn off the block reservation if the goal allocation group has a few (some) free blocks left (not enough for make the desired reservation window),to try to allocation in the goal block group, to get better locality. But if the goal blocks have 0 free blocks, it should leave the block reservation on, and continues search for the next block groups,rather than turn off block reservation completely. 2) we don't need to check the window size if the block reservation is off. The problem was originally found and fixed in ext4. Signed-off-by: Mingming Cao --- fs/ext2/balloc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) Index: linux-2.6.27-rc3/fs/ext2/balloc.c =================================================================== --- linux-2.6.27-rc3.orig/fs/ext2/balloc.c 2008-08-12 18:55:39.000000000 -0700 +++ linux-2.6.27-rc3/fs/ext2/balloc.c 2008-08-28 15:51:59.000000000 -0700 @@ -1295,6 +1295,7 @@ * turn off reservation for this allocation */ if (my_rsv && (free_blocks < windowsz) + && (free_blocks > 0) && (rsv_is_empty(&my_rsv->rsv_window))) my_rsv = NULL; @@ -1332,7 +1333,7 @@ * free blocks is less than half of the reservation * window size. */ - if (free_blocks <= (windowsz/2)) + if (my_rsv && (free_blocks <= (windowsz/2))) continue; brelse(bitmap_bh);