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Date:   Thu, 29 Oct 2020 19:53:31 +0100
From:   David Sterba <dsterba@suse.cz>
To:     Anand Jain <anand.jain@oracle.com>
Cc:     linux-btrfs@vger.kernel.org, Josef Bacik <josef@toxicpanda.com>
Subject: Re: [PATCH v10 2/3] btrfs: create read policy framework
Message-ID: <20201029185331.GS6756@twin.jikos.cz>
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References: <cover.1603884513.git.anand.jain@oracle.com>
 <6cf180d094035e0d9cd6544f60b80d79957a17d9.1603884513.git.anand.jain@oracle.com>
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On Wed, Oct 28, 2020 at 09:14:46PM +0800, Anand Jain wrote:
> @@ -5485,7 +5486,19 @@ static int find_live_mirror(struct btrfs_fs_info *fs_info,
>  	else
>  		num_stripes = map->num_stripes;
>  
> -	preferred_mirror = first + current->pid % num_stripes;
> +	switch (fs_info->fs_devices->read_policy) {
> +	default:
> +		/*
> +		 * Shouldn't happen, just warn and use pid instead of failing.
> +		 */
> +		btrfs_warn_rl(fs_info,
> +			      "unknown read_policy type %u, fallback to pid",
> +			      fs_info->fs_devices->read_policy);

So this would flood the system log with useless messages once this
happens. We should really reset it to pid or whatever default we choose.
Fixed.

> +		fallthrough;
> +	case BTRFS_READ_POLICY_PID:
> +		preferred_mirror = first + current->pid % num_stripes;

This is in the original code, but this should really use ( ) to make the
precedence clear.