diff mbox series

[2/3] mm: Add folio_fill_tail() and use it in iomap

Message ID 20231107212643.3490372-3-willy@infradead.org (mailing list archive)
State New, archived
Headers show
Series Add folio_zero_tail() and folio_fill_tail() | expand

Commit Message

Matthew Wilcox Nov. 7, 2023, 9:26 p.m. UTC
The iomap code was limited to PAGE_SIZE bytes; generalise it to cover
an arbitrary-sized folio, and move it to be a common helper.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/iomap/buffered-io.c  | 14 ++------------
 include/linux/highmem.h | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 12 deletions(-)

Comments

Andreas Gruenbacher Nov. 9, 2023, 9:50 p.m. UTC | #1
On Tue, Nov 7, 2023 at 10:27 PM Matthew Wilcox (Oracle)
<willy@infradead.org> wrote:
> The iomap code was limited to PAGE_SIZE bytes; generalise it to cover
> an arbitrary-sized folio, and move it to be a common helper.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  fs/iomap/buffered-io.c  | 14 ++------------
>  include/linux/highmem.h | 38 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 40 insertions(+), 12 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index f72df2babe56..093c4515b22a 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -305,28 +305,18 @@ static int iomap_read_inline_data(const struct iomap_iter *iter,
>  {
>         const struct iomap *iomap = iomap_iter_srcmap(iter);
>         size_t size = i_size_read(iter->inode) - iomap->offset;
> -       size_t poff = offset_in_page(iomap->offset);
>         size_t offset = offset_in_folio(folio, iomap->offset);
> -       void *addr;
>
>         if (folio_test_uptodate(folio))
>                 return 0;
>
> -       if (WARN_ON_ONCE(size > PAGE_SIZE - poff))
> -               return -EIO;
> -       if (WARN_ON_ONCE(size > PAGE_SIZE -
> -                        offset_in_page(iomap->inline_data)))
> -               return -EIO;
>         if (WARN_ON_ONCE(size > iomap->length))
>                 return -EIO;
>         if (offset > 0)
>                 ifs_alloc(iter->inode, folio, iter->flags);
>
> -       addr = kmap_local_folio(folio, offset);
> -       memcpy(addr, iomap->inline_data, size);
> -       memset(addr + size, 0, PAGE_SIZE - poff - size);
> -       kunmap_local(addr);
> -       iomap_set_range_uptodate(folio, offset, PAGE_SIZE - poff);
> +       folio_fill_tail(folio, offset, iomap->inline_data, size);
> +       iomap_set_range_uptodate(folio, offset, folio_size(folio) - offset);
>         return 0;
>  }
>
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index 1b81416196dd..0fbb60ffefc9 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -521,6 +521,44 @@ static inline __must_check void *folio_zero_tail(struct folio *folio,
>         return kaddr;
>  }
>
> +/**
> + * folio_fill_tail - Copy some data to a folio and pad with zeroes.
> + * @folio: The destination folio.
> + * @offset: The offset into @folio at which to start copying.
> + * @from: The data to copy.
> + * @len: How many bytes of data to copy.
> + *
> + * This function is most useful for filesystems which support inline data.
> + * When they want to copy data from the inode into the page cache, this
> + * function does everything for them.  It supports large folios even on
> + * HIGHMEM configurations.
> + */
> +static inline void folio_fill_tail(struct folio *folio, size_t offset,
> +               const char *from, size_t len)
> +{
> +       char *to = kmap_local_folio(folio, offset);
> +
> +       VM_BUG_ON(offset + len > folio_size(folio));
> +
> +       if (folio_test_highmem(folio)) {
> +               size_t max = PAGE_SIZE - offset_in_page(offset);
> +
> +               while (len > max) {
> +                       memcpy(to, from, max);
> +                       kunmap_local(to);
> +                       len -= max;
> +                       from += max;
> +                       offset += max;
> +                       max = PAGE_SIZE;
> +                       to = kmap_local_folio(folio, offset);
> +               }
> +       }
> +
> +       memcpy(to, from, len);
> +       to = folio_zero_tail(folio, offset, to);

This needs to be:

to = folio_zero_tail(folio, offset  + len, to + len);

> +       kunmap_local(to);
> +}
> +
>  /**
>   * memcpy_from_file_folio - Copy some bytes from a file folio.
>   * @to: The destination buffer.
> --
> 2.42.0
>

Reviewed-by: Andreas Gruenbacher <agruenba@redhat.com>

Thanks,
Andreas
Matthew Wilcox Nov. 10, 2023, 5:09 p.m. UTC | #2
On Thu, Nov 09, 2023 at 10:50:45PM +0100, Andreas Gruenbacher wrote:
> On Tue, Nov 7, 2023 at 10:27 PM Matthew Wilcox (Oracle)
> <willy@infradead.org> wrote:
> > +static inline void folio_fill_tail(struct folio *folio, size_t offset,
> > +               const char *from, size_t len)
> > +{
> > +       char *to = kmap_local_folio(folio, offset);
> > +
> > +       VM_BUG_ON(offset + len > folio_size(folio));
> > +
> > +       if (folio_test_highmem(folio)) {
> > +               size_t max = PAGE_SIZE - offset_in_page(offset);
> > +
> > +               while (len > max) {
> > +                       memcpy(to, from, max);
> > +                       kunmap_local(to);
> > +                       len -= max;
> > +                       from += max;
> > +                       offset += max;
> > +                       max = PAGE_SIZE;
> > +                       to = kmap_local_folio(folio, offset);
> > +               }
> > +       }
> > +
> > +       memcpy(to, from, len);
> > +       to = folio_zero_tail(folio, offset, to);
> 
> This needs to be:
> 
> to = folio_zero_tail(folio, offset  + len, to + len);

Oh, wow, that was stupid of me.  I only ran an xfstests against ext4,
which doesn't exercise this code, not gfs2 or erofs.  Thanks for
fixing this up.

I was wondering about adding the assertion:

	VM_BUG_ON((kaddr - offset) % PAGE_SIZE);

to catch the possible mistake of calling kmap_local_folio(folio, 0)
instead of kmap_local_folio(folio, offset).  But maybe that's
sufficiently unlikely a mistake to bother adding a runtime check for.
Andreas Grünbacher Nov. 10, 2023, 5:50 p.m. UTC | #3
Am Fr., 10. Nov. 2023 um 18:09 Uhr schrieb Matthew Wilcox <willy@infradead.org>:
> On Thu, Nov 09, 2023 at 10:50:45PM +0100, Andreas Gruenbacher wrote:
> > On Tue, Nov 7, 2023 at 10:27 PM Matthew Wilcox (Oracle)
> > <willy@infradead.org> wrote:
> > > +static inline void folio_fill_tail(struct folio *folio, size_t offset,
> > > +               const char *from, size_t len)
> > > +{
> > > +       char *to = kmap_local_folio(folio, offset);
> > > +
> > > +       VM_BUG_ON(offset + len > folio_size(folio));
> > > +
> > > +       if (folio_test_highmem(folio)) {
> > > +               size_t max = PAGE_SIZE - offset_in_page(offset);
> > > +
> > > +               while (len > max) {
> > > +                       memcpy(to, from, max);
> > > +                       kunmap_local(to);
> > > +                       len -= max;
> > > +                       from += max;
> > > +                       offset += max;
> > > +                       max = PAGE_SIZE;
> > > +                       to = kmap_local_folio(folio, offset);
> > > +               }
> > > +       }
> > > +
> > > +       memcpy(to, from, len);
> > > +       to = folio_zero_tail(folio, offset, to);
> >
> > This needs to be:
> >
> > to = folio_zero_tail(folio, offset  + len, to + len);
>
> Oh, wow, that was stupid of me.  I only ran an xfstests against ext4,
> which doesn't exercise this code, not gfs2 or erofs.  Thanks for
> fixing this up.
>
> I was wondering about adding the assertion:
>
>         VM_BUG_ON((kaddr - offset) % PAGE_SIZE);
>
> to catch the possible mistake of calling kmap_local_folio(folio, 0)
> instead of kmap_local_folio(folio, offset).  But maybe that's
> sufficiently unlikely a mistake to bother adding a runtime check for.

folio_zero_tail() is a bit of an obscure function, so I'm not sure if
there will be additional callers. The parameters are described as:

 * @offset: The byte offset in the folio to start zeroing at.
 * @kaddr: The address the folio is currently mapped to.

What about changing the @kaddr description to 'the (mapped) address
within the folio to start zeroing at' or similar?

Andreas
Gao Xiang Nov. 11, 2023, 4:02 a.m. UTC | #4
On 2023/11/11 01:09, Matthew Wilcox wrote:
> On Thu, Nov 09, 2023 at 10:50:45PM +0100, Andreas Gruenbacher wrote:
>> On Tue, Nov 7, 2023 at 10:27 PM Matthew Wilcox (Oracle)
>> <willy@infradead.org> wrote:
>>> +static inline void folio_fill_tail(struct folio *folio, size_t offset,
>>> +               const char *from, size_t len)
>>> +{
>>> +       char *to = kmap_local_folio(folio, offset);
>>> +
>>> +       VM_BUG_ON(offset + len > folio_size(folio));
>>> +
>>> +       if (folio_test_highmem(folio)) {
>>> +               size_t max = PAGE_SIZE - offset_in_page(offset);
>>> +
>>> +               while (len > max) {
>>> +                       memcpy(to, from, max);
>>> +                       kunmap_local(to);
>>> +                       len -= max;
>>> +                       from += max;
>>> +                       offset += max;
>>> +                       max = PAGE_SIZE;
>>> +                       to = kmap_local_folio(folio, offset);
>>> +               }
>>> +       }
>>> +
>>> +       memcpy(to, from, len);
>>> +       to = folio_zero_tail(folio, offset, to);
>>
>> This needs to be:
>>
>> to = folio_zero_tail(folio, offset  + len, to + len);
> 
> Oh, wow, that was stupid of me.  I only ran an xfstests against ext4,
> which doesn't exercise this code, not gfs2 or erofs.  Thanks for
> fixing this up.

Assuming that is for the next cycle (no rush), I will also test
this patch and feedback later since I'm now working on other
stuffs.

Thanks,
Gao Xiang
diff mbox series

Patch

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index f72df2babe56..093c4515b22a 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -305,28 +305,18 @@  static int iomap_read_inline_data(const struct iomap_iter *iter,
 {
 	const struct iomap *iomap = iomap_iter_srcmap(iter);
 	size_t size = i_size_read(iter->inode) - iomap->offset;
-	size_t poff = offset_in_page(iomap->offset);
 	size_t offset = offset_in_folio(folio, iomap->offset);
-	void *addr;
 
 	if (folio_test_uptodate(folio))
 		return 0;
 
-	if (WARN_ON_ONCE(size > PAGE_SIZE - poff))
-		return -EIO;
-	if (WARN_ON_ONCE(size > PAGE_SIZE -
-			 offset_in_page(iomap->inline_data)))
-		return -EIO;
 	if (WARN_ON_ONCE(size > iomap->length))
 		return -EIO;
 	if (offset > 0)
 		ifs_alloc(iter->inode, folio, iter->flags);
 
-	addr = kmap_local_folio(folio, offset);
-	memcpy(addr, iomap->inline_data, size);
-	memset(addr + size, 0, PAGE_SIZE - poff - size);
-	kunmap_local(addr);
-	iomap_set_range_uptodate(folio, offset, PAGE_SIZE - poff);
+	folio_fill_tail(folio, offset, iomap->inline_data, size);
+	iomap_set_range_uptodate(folio, offset, folio_size(folio) - offset);
 	return 0;
 }
 
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 1b81416196dd..0fbb60ffefc9 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -521,6 +521,44 @@  static inline __must_check void *folio_zero_tail(struct folio *folio,
 	return kaddr;
 }
 
+/**
+ * folio_fill_tail - Copy some data to a folio and pad with zeroes.
+ * @folio: The destination folio.
+ * @offset: The offset into @folio at which to start copying.
+ * @from: The data to copy.
+ * @len: How many bytes of data to copy.
+ *
+ * This function is most useful for filesystems which support inline data.
+ * When they want to copy data from the inode into the page cache, this
+ * function does everything for them.  It supports large folios even on
+ * HIGHMEM configurations.
+ */
+static inline void folio_fill_tail(struct folio *folio, size_t offset,
+		const char *from, size_t len)
+{
+	char *to = kmap_local_folio(folio, offset);
+
+	VM_BUG_ON(offset + len > folio_size(folio));
+
+	if (folio_test_highmem(folio)) {
+		size_t max = PAGE_SIZE - offset_in_page(offset);
+
+		while (len > max) {
+			memcpy(to, from, max);
+			kunmap_local(to);
+			len -= max;
+			from += max;
+			offset += max;
+			max = PAGE_SIZE;
+			to = kmap_local_folio(folio, offset);
+		}
+	}
+
+	memcpy(to, from, len);
+	to = folio_zero_tail(folio, offset, to);
+	kunmap_local(to);
+}
+
 /**
  * memcpy_from_file_folio - Copy some bytes from a file folio.
  * @to: The destination buffer.