On 24.04.2018 02:03, David Sterba wrote:
> The eb length is nodesize, as initialized in __alloc_extent_buffer.
> Regardless of start, we should always get the same number of pages, so
> use that fact.
>
> Signed-off-by: David Sterba <dsterba@xxxxxxxx>
> ---
> fs/btrfs/extent_io.h | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
> index a53009694b16..ee92c1289edd 100644
> --- a/fs/btrfs/extent_io.h
> +++ b/fs/btrfs/extent_io.h
> @@ -454,8 +454,7 @@ void wait_on_extent_buffer_writeback(struct extent_buffer *eb);
>
> static inline unsigned long num_extent_pages(u64 start, u64 len)
> {
> - return ((start + len + PAGE_SIZE - 1) >> PAGE_SHIFT) -
> - (start >> PAGE_SHIFT);
> + return len >> PAGE_SHIFT;
Shouldn't this really be len + PAGE_SIZE -1 or in fact DIV_ROUND_DOWN
(len, PAGE_SIZE). Because with a nodesize of 4k (and basically less than
a page size) we can get into a situation where we do:
4096 >> 13 = 0
On powerpc for example we have:
arch/powerpc/include/asm/page.h:#define PAGE_SHIFT 18
arch/powerpc/include/asm/page.h:#define PAGE_SHIFT 16
arch/powerpc/include/asm/page.h:#define PAGE_SHIFT 14
arch/powerpc/include/asm/page.h:#define PAGE_SHIFT 12
> }
>
> static inline void extent_buffer_get(struct extent_buffer *eb)
>
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