linux-kernel - Re: [PATCH v8 3/7] fsdax: Replace mmap entry in case of CoW

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Date:   Thu, 2 Sep 2021 09:27:19 +0200
From:   Christoph Hellwig <hch@....de>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     djwong@...nel.org, hch@....de, linux-xfs@...r.kernel.org,
        dan.j.williams@...el.com, david@...morbit.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        nvdimm@...ts.linux.dev, rgoldwyn@...e.de, viro@...iv.linux.org.uk,
        willy@...radead.org, Goldwyn Rodrigues <rgoldwyn@...e.com>,
        Ritesh Harjani <riteshh@...ux.ibm.com>
Subject: Re: [PATCH v8 3/7] fsdax: Replace mmap entry in case of CoW

On Sun, Aug 29, 2021 at 08:25:13PM +0800, Shiyang Ruan wrote:
> We replace the existing entry to the newly allocated one in case of CoW.
> Also, we mark the entry as PAGECACHE_TAG_TOWRITE so writeback marks this
> entry as writeprotected.  This helps us snapshots so new write
> pagefaults after snapshots trigger a CoW.

Nit: s/We r/R/ above.

> + * MAP_SYNC on a dax mapping guarantees dirty metadata is
> + * flushed on write-faults (non-cow), but not read-faults.
> + */
> +static bool dax_fault_is_synchronous(const struct iomap_iter *iter,
> +		struct vm_area_struct *vma)
> +{
> +	return (iter->flags & IOMAP_WRITE) && (vma->vm_flags & VM_SYNC)
> +		&& (iter->iomap.flags & IOMAP_F_DIRTY);
> +}
> +
> +static bool dax_fault_is_cow(const struct iomap_iter *iter)
> +{
> +	return (iter->flags & IOMAP_WRITE)
> +		&& (iter->iomap.flags & IOMAP_F_SHARED);
> +}

The && goes last on the first line, not at the beginning of the second.