On Sat, Jul 24, 2021 at 12:46:45PM +0800, Gao Xiang wrote:
> Hi Matthew,
>
> On Sat, Jul 24, 2021 at 04:44:35AM +0100, Matthew Wilcox (Oracle) wrote:
> > Remove the restriction that inline data must start on a page boundary
> > in a file. This allows, for example, the first 2KiB to be stored out
> > of line and the trailing 30 bytes to be stored inline.
> >
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> > ---
> > fs/iomap/buffered-io.c | 18 ++++++++----------
> > 1 file changed, 8 insertions(+), 10 deletions(-)
> >
> > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> > index 7bd8e5de996d..d7d6af29af7f 100644
> > --- a/fs/iomap/buffered-io.c
> > +++ b/fs/iomap/buffered-io.c
> > @@ -209,25 +209,23 @@ static int iomap_read_inline_data(struct inode *inode, struct page *page,
> > struct iomap *iomap, loff_t pos)
> > {
> > size_t size = iomap->length + iomap->offset - pos;
> > + size_t poff = offset_in_page(pos);
> > void *addr;
> >
> > if (PageUptodate(page))
> > - return PAGE_SIZE;
> > + return PAGE_SIZE - poff;
> >
> > - /* inline data must start page aligned in the file */
> > - if (WARN_ON_ONCE(offset_in_page(pos)))
> > - return -EIO;
> > if (WARN_ON_ONCE(!iomap_inline_data_size_valid(iomap)))
> > return -EIO;
> > - if (WARN_ON_ONCE(page_has_private(page)))
> > - return -EIO;
> > + if (poff > 0)
> > + iomap_page_create(inode, page);
>
> Thanks for the patch!
>
> Previously I'd like to skip the leading uptodate blocks and update the
> extent it covers that is due to already exist iop. If we get rid of the
> offset_in_page(pos) restriction like this, I'm not sure if we (or some
> other fs users) could face something like below (due to somewhat buggy
> fs users likewise):
>
> [0 - 4096) plain block
>
> [4096 - 4608) tail INLINE 1 (e.g. by mistake or just splitted
> .iomap_begin() report.)
> [4608 - 5120] tail INLINE 2
My assumption is that an INLINE extent is <= block_size. Otherwise
the first part of the extent would be not-inline. So this would be
a bug in the filesystem; [4096-4608) should not be an inline extent.
> with this code iomap_set_range_uptodate() wouldn't behave correctly.
>
> In addition, currently EROFS cannot test such path (since EROFS is
> page-sized block only for now) as Darrick said in the previous reply,
> so I think it would be better together with the folio patchset and
> targeted for the corresponding merge window, so I can test iomap
> supported EROFS with the new folio support together (That also give
> me some time to support sub-pagesized uncompressed blocks...)
Do you want to test erofs with multi-page folios? That might be
even more interesting than block size < page size.
> > - addr = kmap_atomic(page);
> > + addr = kmap_atomic(page) + poff;
> > memcpy(addr, iomap_inline_buf(iomap, pos), size);
> > - memset(addr + size, 0, PAGE_SIZE - size);
> > + memset(addr + size, 0, PAGE_SIZE - poff - size);
> > kunmap_atomic(addr);
>
> As my limited understanding, this may need to be fixed, since it
> doesn't match kmap_atomic(page)...
void kunmap_local_indexed(void *vaddr)
{
unsigned long addr = (unsigned long) vaddr & PAGE_MASK;
so it's fine to unmap any address in the page.
