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Message-ID: <20200825222355.GL6096@magnolia>
Date: Tue, 25 Aug 2020 15:23:55 -0700
From: "Darrick J. Wong" <darrick.wong@...cle.com>
To: "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-nvdimm@...ts.01.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 9/9] iomap: Change calling convention for zeroing
On Mon, Aug 24, 2020 at 03:55:10PM +0100, Matthew Wilcox (Oracle) wrote:
> Pass the full length to iomap_zero() and dax_iomap_zero(), and have
> them return how many bytes they actually handled. This is preparatory
> work for handling THP, although it looks like DAX could actually take
> advantage of it if there's a larger contiguous area.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
> fs/dax.c | 13 ++++++-------
> fs/iomap/buffered-io.c | 33 +++++++++++++++------------------
> include/linux/dax.h | 3 +--
> 3 files changed, 22 insertions(+), 27 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 95341af1a966..f2b912cb034e 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1037,18 +1037,18 @@ static vm_fault_t dax_load_hole(struct xa_state *xas,
> return ret;
> }
>
> -int dax_iomap_zero(loff_t pos, unsigned offset, unsigned size,
> - struct iomap *iomap)
> +loff_t dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
Sorry for my ultra-slow response to this. The u64 length seems ok to me
(or uint64_t, I don't care all /that/ much), but using loff_t as a
return type bothers me because I see that and think that this function
is returning a new file offset, e.g. (pos + number of bytes zeroed).
So please, let's use s64 or something that isn't so misleading.
FWIW, Linus also[0] doesn't[1] like using loff_t for the number of bytes
copied.
--D
[0] https://lore.kernel.org/linux-fsdevel/CAHk-=wgcPAfOSigMf0xwaGfVjw413XN3UPATwYWHrss+QuivhQ@mail.gmail.com/
[1] https://lore.kernel.org/linux-fsdevel/CAHk-=wgvROUnrEVADVR_zTHY8NmYo-_jVjV37O1MdDm2de+Lmw@mail.gmail.com/
> {
> sector_t sector = iomap_sector(iomap, pos & PAGE_MASK);
> pgoff_t pgoff;
> long rc, id;
> void *kaddr;
> bool page_aligned = false;
> -
> + unsigned offset = offset_in_page(pos);
> + unsigned size = min_t(u64, PAGE_SIZE - offset, length);
>
> if (IS_ALIGNED(sector << SECTOR_SHIFT, PAGE_SIZE) &&
> - IS_ALIGNED(size, PAGE_SIZE))
> + (size == PAGE_SIZE))
> page_aligned = true;
>
> rc = bdev_dax_pgoff(iomap->bdev, sector, PAGE_SIZE, &pgoff);
> @@ -1058,8 +1058,7 @@ int dax_iomap_zero(loff_t pos, unsigned offset, unsigned size,
> id = dax_read_lock();
>
> if (page_aligned)
> - rc = dax_zero_page_range(iomap->dax_dev, pgoff,
> - size >> PAGE_SHIFT);
> + rc = dax_zero_page_range(iomap->dax_dev, pgoff, 1);
> else
> rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);
> if (rc < 0) {
> @@ -1072,7 +1071,7 @@ int dax_iomap_zero(loff_t pos, unsigned offset, unsigned size,
> dax_flush(iomap->dax_dev, kaddr + offset, size);
> }
> dax_read_unlock(id);
> - return 0;
> + return size;
> }
>
> static loff_t
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 7f618ab4b11e..2dba054095e8 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -901,11 +901,13 @@ iomap_file_unshare(struct inode *inode, loff_t pos, loff_t len,
> }
> EXPORT_SYMBOL_GPL(iomap_file_unshare);
>
> -static int iomap_zero(struct inode *inode, loff_t pos, unsigned offset,
> - unsigned bytes, struct iomap *iomap, struct iomap *srcmap)
> +static loff_t iomap_zero(struct inode *inode, loff_t pos, u64 length,
> + struct iomap *iomap, struct iomap *srcmap)
> {
> struct page *page;
> int status;
> + unsigned offset = offset_in_page(pos);
> + unsigned bytes = min_t(u64, PAGE_SIZE - offset, length);
>
> status = iomap_write_begin(inode, pos, bytes, 0, &page, iomap, srcmap);
> if (status)
> @@ -917,38 +919,33 @@ static int iomap_zero(struct inode *inode, loff_t pos, unsigned offset,
> return iomap_write_end(inode, pos, bytes, bytes, page, iomap, srcmap);
> }
>
> -static loff_t
> -iomap_zero_range_actor(struct inode *inode, loff_t pos, loff_t count,
> - void *data, struct iomap *iomap, struct iomap *srcmap)
> +static loff_t iomap_zero_range_actor(struct inode *inode, loff_t pos,
> + loff_t length, void *data, struct iomap *iomap,
> + struct iomap *srcmap)
> {
> bool *did_zero = data;
> loff_t written = 0;
> - int status;
>
> /* already zeroed? we're done. */
> if (srcmap->type == IOMAP_HOLE || srcmap->type == IOMAP_UNWRITTEN)
> - return count;
> + return length;
>
> do {
> - unsigned offset, bytes;
> -
> - offset = offset_in_page(pos);
> - bytes = min_t(loff_t, PAGE_SIZE - offset, count);
> + loff_t bytes;
>
> if (IS_DAX(inode))
> - status = dax_iomap_zero(pos, offset, bytes, iomap);
> + bytes = dax_iomap_zero(pos, length, iomap);
> else
> - status = iomap_zero(inode, pos, offset, bytes, iomap,
> - srcmap);
> - if (status < 0)
> - return status;
> + bytes = iomap_zero(inode, pos, length, iomap, srcmap);
> + if (bytes < 0)
> + return bytes;
>
> pos += bytes;
> - count -= bytes;
> + length -= bytes;
> written += bytes;
> if (did_zero)
> *did_zero = true;
> - } while (count > 0);
> + } while (length > 0);
>
> return written;
> }
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index 6904d4e0b2e0..80f17946f940 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -214,8 +214,7 @@ vm_fault_t dax_finish_sync_fault(struct vm_fault *vmf,
> int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index);
> int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
> pgoff_t index);
> -int dax_iomap_zero(loff_t pos, unsigned offset, unsigned size,
> - struct iomap *iomap);
> +loff_t dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap);
> static inline bool dax_mapping(struct address_space *mapping)
> {
> return mapping->host && IS_DAX(mapping->host);
> --
> 2.28.0
>
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