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Date: Fri, 9 Feb 2024 16:44:22 +0900
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Subject: Re: [PATCH v3 1/5] zonefs: pass GFP_KERNEL to blkdev_zone_mgmt() call
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To: Johannes Thumshirn <johannes.thumshirn@wdc.com>,
 Naohiro Aota <naohiro.aota@wdc.com>, Johannes Thumshirn <jth@kernel.org>,
 Alasdair Kergon <agk@redhat.com>, Mike Snitzer <snitzer@kernel.org>,
 Mikulas Patocka <mpatocka@redhat.com>, dm-devel@lists.linux.dev,
 Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>,
 David Sterba <dsterba@suse.com>, Jaegeuk Kim <jaegeuk@kernel.org>,
 Chao Yu <chao@kernel.org>, Jens Axboe <axboe@kernel.dk>,
 Christoph Hellwig <hch@lst.de>, Sagi Grimberg <sagi@grimberg.me>,
 Chaitanya Kulkarni <kch@nvidia.com>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
 linux-btrfs@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net,
 linux-block@vger.kernel.org, linux-nvme@lists.infradead.org
References: <20240128-zonefs_nofs-v3-0-ae3b7c8def61@wdc.com>
 <20240128-zonefs_nofs-v3-1-ae3b7c8def61@wdc.com>
From: Damien Le Moal <dlemoal@kernel.org>
Organization: Western Digital Research
In-Reply-To: <20240128-zonefs_nofs-v3-1-ae3b7c8def61@wdc.com>
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On 1/29/24 16:52, Johannes Thumshirn wrote:
> Pass GFP_KERNEL instead of GFP_NOFS to the blkdev_zone_mgmt() call in
> zonefs_zone_mgmt().
> 
> As as zonefs_zone_mgmt() and zonefs_inode_zone_mgmt() are never called
> from a place that can recurse back into the filesystem on memory reclaim,
> it is save to call blkdev_zone_mgmt() with GFP_KERNEL.
> 
> Link: https://lore.kernel.org/all/ZZcgXI46AinlcBDP@casper.infradead.org/
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> ---
>  fs/zonefs/super.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/zonefs/super.c b/fs/zonefs/super.c
> index 93971742613a..63fbac018c04 100644
> --- a/fs/zonefs/super.c
> +++ b/fs/zonefs/super.c
> @@ -113,7 +113,7 @@ static int zonefs_zone_mgmt(struct super_block *sb,
>  
>  	trace_zonefs_zone_mgmt(sb, z, op);
>  	ret = blkdev_zone_mgmt(sb->s_bdev, op, z->z_sector,
> -			       z->z_size >> SECTOR_SHIFT, GFP_NOFS);
> +			       z->z_size >> SECTOR_SHIFT, GFP_KERNEL);
>  	if (ret) {
>  		zonefs_err(sb,
>  			   "Zone management operation %s at %llu failed %d\n",
> 

Given that zonefs_inode_zone_mgmt() which calls zonefs_zone_mgmt() is only used
for sequential zone inodes, and that these inodes cannot be written with
buffered IOs, I think this is safe as we will never have dirty pages to
writeback for reclaim. So there should be no risk of re-entering the FS on
reclaim with GFP_KERNEL.

So:

Acked-by: Damien Le Moal <dlemoal@kernel.org>

-- 
Damien Le Moal
Western Digital Research