linux-kernel - Re: [PATCH v3 06/11] mm, pmem: Implement ->memory

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Date:   Wed, 10 Feb 2021 14:41:00 +0100
From:   Christoph Hellwig <hch@....de>
To:     Shiyang Ruan <ruansy.fnst@...fujitsu.com>
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, dm-devel@...hat.com,
        darrick.wong@...cle.com, dan.j.williams@...el.com,
        david@...morbit.com, hch@....de, agk@...hat.com,
        snitzer@...hat.com, rgoldwyn@...e.de, qi.fuli@...itsu.com,
        y-goto@...itsu.com
Subject: Re: [PATCH v3 06/11] mm, pmem: Implement ->memory_failure() in
 pmem driver

> +static int pmem_pagemap_memory_failure(struct dev_pagemap *pgmap,
> +		unsigned long pfn, int flags)
> +{
> +	struct pmem_device *pdev;
> +	struct gendisk *disk;
> +	loff_t disk_offset;
> +	int rc = 0;
> +	unsigned long size = page_size(pfn_to_page(pfn));
> +
> +	pdev = container_of(pgmap, struct pmem_device, pgmap);
> +	disk = pdev->disk;

Would be nice to initialize this at the time of declaration:

	struct pmem_device *pdev =
		container_of(pgmap, struct pmem_device, pgmap);
	struct gendisk *disk = pdev->disk
	unsigned long size = page_size(pfn_to_page(pfn));

> +	if (!disk)
> +		return -ENXIO;
> +
> +	disk_offset = PFN_PHYS(pfn) - pdev->phys_addr - pdev->data_offset;
> +	if (disk->fops->corrupted_range) {
> +		rc = disk->fops->corrupted_range(disk, NULL, disk_offset,
> +						 size, &flags);
> +		if (rc == -ENODEV)
> +			rc = -ENXIO;
> +	} else
> +		rc = -EOPNOTSUPP;

Why do we need the disk and fops check here? A pgmap registered by pmem.c
should always have a disk with pmem_fops.  And more importantly this
has no business going through the block layer.

Instead the file system should deposit a callback when starting to use
the dax_device using fs_dax_get_by_bdev / dax_get_by_host and a private
data (the superblock), and we avoid all the lookup problems.

> +int mf_generic_kill_procs(unsigned long long pfn, int flags)

This function seems to be only used inside of memory-failure.c, so it
could be marked static.  Also I'd name it dax_generic_memory_failure
or something like that to match the naming of the ->memory_failure
pgmap operation.

Also maybe just splitting this out into a helper would be a nice prep
patch.