linux-kernel - Re: [PATCH v8 06/11] btrfs: implement RST version of scrub

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Message-ID: <20230913165948.GS20408@twin.jikos.cz>
Date:   Wed, 13 Sep 2023 18:59:48 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Johannes Thumshirn <johannes.thumshirn@....com>
Cc:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Christoph Hellwig <hch@....de>,
        Naohiro Aota <naohiro.aota@....com>, Qu Wenruo <wqu@...e.com>,
        Damien Le Moal <dlemoal@...nel.org>,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 06/11] btrfs: implement RST version of scrub

On Mon, Sep 11, 2023 at 05:52:07AM -0700, Johannes Thumshirn wrote:
> A filesystem that uses the RAID stripe tree for logical to physical
> address translation can't use the regular scrub path, that reads all
> stripes and then checks if a sector is unused afterwards.
> 
> When using the RAID stripe tree, this will result in lookup errors, as the
> stripe tree doesn't know the requested logical addresses.
> 
> Instead, look up stripes that are backed by the extent bitmap.
> 
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@....com>
> ---
>  fs/btrfs/scrub.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 56 insertions(+)
> 
> diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
> index f16220ce5fba..5101e0a3f83e 100644
> --- a/fs/btrfs/scrub.c
> +++ b/fs/btrfs/scrub.c
> @@ -23,6 +23,7 @@
>  #include "accessors.h"
>  #include "file-item.h"
>  #include "scrub.h"
> +#include "raid-stripe-tree.h"
>  
>  /*
>   * This is only the first step towards a full-features scrub. It reads all
> @@ -1634,6 +1635,56 @@ static void scrub_reset_stripe(struct scrub_stripe *stripe)
>  	}
>  }
>  
> +static void scrub_submit_extent_sector_read(struct scrub_ctx *sctx,
> +					    struct scrub_stripe *stripe)
> +{
> +	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
> +	struct btrfs_bio *bbio = NULL;
> +	int mirror = stripe->mirror_num;
> +	int i;
> +
> +	atomic_inc(&stripe->pending_io);
> +
> +	for_each_set_bit(i, &stripe->extent_sector_bitmap, stripe->nr_sectors) {
> +		struct page *page;
> +		int pgoff;

This should be unsigned int.

> +
> +		page = scrub_stripe_get_page(stripe, i);
> +		pgoff = scrub_stripe_get_page_offset(stripe, i);

You can probably move the initializations right to the declarations, I
think we have that elsewhere too.

> +		/* The current sector cannot be merged, submit the bio. */
> +		if (bbio &&
> +		    ((i > 0 && !test_bit(i - 1, &stripe->extent_sector_bitmap)) ||
> +		     bbio->bio.bi_iter.bi_size >= BTRFS_STRIPE_LEN)) {
> +			ASSERT(bbio->bio.bi_iter.bi_size);
> +			atomic_inc(&stripe->pending_io);
> +			btrfs_submit_bio(bbio, mirror);
> +			bbio = NULL;
> +		}
> +
> +		if (!bbio) {
> +			bbio = btrfs_bio_alloc(stripe->nr_sectors, REQ_OP_READ,
> +				fs_info, scrub_read_endio, stripe);
> +			bbio->bio.bi_iter.bi_sector = (stripe->logical +
> +				(i << fs_info->sectorsize_bits)) >> SECTOR_SHIFT;
> +		}
> +
> +		__bio_add_page(&bbio->bio, page, fs_info->sectorsize, pgoff);
> +	}
> +
> +	if (bbio) {
> +		ASSERT(bbio->bio.bi_iter.bi_size);
> +		atomic_inc(&stripe->pending_io);
> +		btrfs_submit_bio(bbio, mirror);
> +	}
> +
> +	if (atomic_dec_and_test(&stripe->pending_io)) {
> +		wake_up(&stripe->io_wait);
> +		INIT_WORK(&stripe->work, scrub_stripe_read_repair_worker);
> +		queue_work(stripe->bg->fs_info->scrub_workers, &stripe->work);
> +	}
> +}