Re: [oops, 4.4-rc8] warn + oops during generic/204

[Jaegeuk Kim <jaegeuk@kernel.org>]

On Thu, Jan 21, 2016 at 07:46:10PM +0800, Chao Yu wrote:
> Hi Dave,
> 
> > -----Original Message-----
> > From: Dave Chinner [mailto:david@fromorbit.com]
> > Sent: Thursday, January 21, 2016 5:31 AM
> > To: linux-f2fs-devel@lists.sourceforge.net
> > Subject: [f2fs-dev] [oops, 4.4-rc8] warn + oops during generic/204
> > 
> > Hi f2fs folks,
> > 
> > I just ran xfstests on f2fs using defaults and a pair of 4GB ram
> > disks for the test and scratch devices, and it hard locked the
> > machine with this failure in generic/204:
> 
> Thanks for your report! :)
> 
> Hi all,
> 
> We didn't handle well with the case of inline data storm which floods
> full disk. Actually the reason is: if we have 10M free space, and user
> fillings the disk with ~10M inline data, then in memory there are ~10M
> dirty inline datas and ~10M dirty inodes, once inodes were writebacked
> before inline datas, all free space will be occupied, then we have to
> write these dirty inline datas to ovp area which doesn't have enough
> space there normally.

Well, I think the user block count was wrong which is determined by mkfs.f2fs.
When writing inline_data, gc should activate to reclaim the space, but it
seems it couldn't do that cause there is no victim.
So, when taking a look at mkfs, I suspect that the number of total user blocks
does not consider our current segments, which is 6 by default.
IOWs, we gave more blocks to users, which turns out actually gc couldn't get a
victim from them in this case.

I could reproduce this issue, and once I reduced the number by 6 segments,
I could avoid the issue.

Here the change of f2fs-tools.

>From 411166a44009bb138eca937376863e9ce673278a Mon Sep 17 00:00:00 2001
From: Jaegeuk Kim <jaegeuk@kernel.org>
Date: Thu, 21 Jan 2016 05:16:37 -0800
Subject: [PATCH] mkfs.f2fs: adjust current segments for total usable blocks

When calculating total number of user blocks, we should reserve the current
segments.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
---
 mkfs/f2fs_format.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mkfs/f2fs_format.c b/mkfs/f2fs_format.c
index 2c81ecc..b25a490 100644
--- a/mkfs/f2fs_format.c
+++ b/mkfs/f2fs_format.c
@@ -474,7 +474,12 @@ static int f2fs_write_check_point_pack(void)
 
 	/* main segments - reserved segments - (node + data segments) */
 	set_cp(free_segment_count, get_sb(segment_count_main) - 6);
-	set_cp(user_block_count, ((get_cp(free_segment_count) + 6 -
+	if (get_cp(free_segment_count) <= get_cp(overprov_segment_count)) {
+		MSG(0, "Error: Too small size\n");
+		goto free_sum_compact;
+	}
+
+	set_cp(user_block_count, ((get_cp(free_segment_count) -
 			get_cp(overprov_segment_count)) * config.blks_per_seg));
 	/* cp page (2), data summaries (1), node summaries (3) */
 	set_cp(cp_pack_total_block_count, 6 + get_sb(cp_payload));
-- 
2.6.3


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