Re: [PATCH] btrfs-progs: check: skip shared node or leaf check for low_memory mode

[Wang Xiaoguang <wangxg.fnst@cn.fujitsu.com>]

Hi,

On 08/24/2016 08:44 PM, David Sterba wrote:
> On Fri, Aug 19, 2016 at 05:59:46PM +0800, Wang Xiaoguang wrote:
>> The basic idea is simple. Assume a middle tree node A is shared and
>> its referenceing fs/file tree root ids are 5, 258 and 260, then we
>> only check node A in the tree who has the smallest root id. That means
>> in this case, when checking root tree(5), we check inode A, for root
>> tree 258 and 260, we can just skip it.
>>
>> Notice even with this patch, we still may visit a shared node or leaf
>> multiple times. This happens when a inode metadata occupies multiple
>> leaves.
>>
>>                   leaf_A     leaf_B
>> When checking inode item in leaf_A, assume inode[512] have file extents
>> in leaf_B, and leaf_B is shared. In the case, for inode[512], we must
>> visit leaf_B to have inode item check. After finishing inode[512] check,
>> here we walk down tree root to leaf_B to check whether node or leaf
>> is shared, if some node or leaf is shared, we can just skip it and below
>> nodes or leaf's check.
>>
>> I also fill a disk partition with linux source codes and create 3 snapshots
>> in it. Before this patch, it averagely took 46s to finish one btrfsck
>> execution, with this patch, it averagely took 15s.
>>
>> Signed-off-by: Wang Xiaoguang <wangxg.fnst@cn.fujitsu.com>
> Can you please refresh the patch on top of current devel branch? I get
> too many conflicts to resolve.
This patch is to improve low memory mode fs/file tree check, but it seems
Lu Fengqi's low memory fs/file tree check patches are not merged into your
devel branch :)

>
>> @@ -2001,6 +2081,7 @@ static int walk_down_tree(struct btrfs_root *root, struct btrfs_path *path,
>>   				       path->nodes[*level]->start,
>>   				       *level, 1, &refs, NULL);
>>   		if (ret < 0) {
>> +			fprintf(stderr, "zhaoyan\n");
> Probably a debugging leftover
:)  I'll remove it.

Regards,
Xiaoguang Wang

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