linux-kernel - Re: [PATCH v2] btrfs: stripe-tree: correctly truncate stripe extents on delete

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Message-ID: <20240923153527.GC159452@perftesting>
Date: Mon, 23 Sep 2024 11:35:27 -0400
From: Josef Bacik <josef@...icpanda.com>
To: Johannes Thumshirn <jth@...nel.org>
Cc: Chris Mason <clm@...com>, David Sterba <dsterba@...e.com>,
	"open list:BTRFS FILE SYSTEM" <linux-btrfs@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>,
	Johannes Thumshirn <johannes.thumshirn@....com>
Subject: Re: [PATCH v2] btrfs: stripe-tree: correctly truncate stripe extents
 on delete

On Wed, Sep 11, 2024 at 11:52:05AM +0200, Johannes Thumshirn wrote:
> From: Johannes Thumshirn <johannes.thumshirn@....com>
> 
> In our CI system, we're seeing the following ASSERT()ion to trigger when
> running RAID stripe-tree tests on non-zoned devices:
> 
>  assertion failed: found_start >= start && found_end <= end, in fs/btrfs/raid-stripe-tree.c:64
> 
> This ASSERT()ion triggers, because for the initial design of RAID stripe-tree,
> I had the "one ordered-extent equals one bio" rule of zoned btrfs in mind.
> 
> But for a RAID stripe-tree based system, that is not hosted on a zoned
> storage device, but on a regular device this rule doesn't apply.
> 
> So in case the range we want to delete starts in the middle of the
> previous item, grab the item and "truncate" it's length. That is, subtract
> the deleted portion from the key's offset.
> 
> In case the range to delete ends in the middle of an item, we have to
> adjust both the item's key as well as the stripe extents.
> 
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@....com>
> ---
> 
> Changes to v1:
> - ASSERT() that slot > 0 before calling btrfs_previous_item()
> 
>  fs/btrfs/raid-stripe-tree.c | 52 ++++++++++++++++++++++++++++++++++++-
>  1 file changed, 51 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/raid-stripe-tree.c b/fs/btrfs/raid-stripe-tree.c
> index 4c859b550f6c..075fecd08d87 100644
> --- a/fs/btrfs/raid-stripe-tree.c
> +++ b/fs/btrfs/raid-stripe-tree.c
> @@ -61,7 +61,57 @@ int btrfs_delete_raid_extent(struct btrfs_trans_handle *trans, u64 start, u64 le
>  		trace_btrfs_raid_extent_delete(fs_info, start, end,
>  					       found_start, found_end);
>  
> -		ASSERT(found_start >= start && found_end <= end);
> +		if (found_start < start) {
> +			struct btrfs_key prev;
> +			u64 diff = start - found_start;
> +
> +			ASSERT(slot > 0);
> +
> +			ret = btrfs_previous_item(stripe_root, path, start,
> +						  BTRFS_RAID_STRIPE_KEY);
> +			leaf = path->nodes[0];
> +			slot = path->slots[0];
> +			btrfs_item_key_to_cpu(leaf, &prev, slot);
> +			prev.offset -= diff;
> +
> +			btrfs_mark_buffer_dirty(trans, leaf);
> +
> +			start += diff;
> +			length -= diff;
> +
> +			btrfs_release_path(path);
> +			continue;
> +		}
> +
> +		if (end < found_end && found_end - end < key.offset) {
> +			struct btrfs_stripe_extent *stripe_extent;
> +			u64 diff = key.offset - length;
> +			int num_stripes;
> +
> +			num_stripes = btrfs_num_raid_stripes(
> +				btrfs_item_size(leaf, slot));
> +			stripe_extent = btrfs_item_ptr(
> +				leaf, slot, struct btrfs_stripe_extent);
> +
> +			for (int i = 0; i < num_stripes; i++) {
> +				struct btrfs_raid_stride *stride =
> +					&stripe_extent->strides[i];
> +				u64 physical = btrfs_raid_stride_physical(
> +					leaf, stride);
> +
> +				physical += diff;
> +				btrfs_set_raid_stride_physical(leaf, stride,
> +							       physical);
> +			}
> +
> +			key.objectid += diff;
> +			key.offset -= diff;

This part was confusing and isn't necessary, you can drop this bit and then add

Reviewed-by: Josef Bacik <josef@...icpanda.com>

Thanks,

Josef