On Thu, 2008-05-22 at 23:56 +0530, Aneesh Kumar K.V wrote:
> On Thu, May 22, 2008 at 11:10:17AM -0700, Mingming wrote:
> >
> > On Wed, 2008-05-21 at 23:14 +0530, Aneesh Kumar K.V wrote:
> > > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> > > ---
> > > fs/ext4/inode.c | 10 +++++++---
> > > 1 files changed, 7 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > > index 46cc610..076d00f 100644
> > > --- a/fs/ext4/inode.c
> > > +++ b/fs/ext4/inode.c
> > > @@ -1571,13 +1571,17 @@ static int ext4_da_writepages(struct address_space *mapping,
> > > */
> > > if (wbc->nr_to_write > EXT4_MAX_WRITEBACK_PAGES)
> > > wbc->nr_to_write = EXT4_MAX_WRITEBACK_PAGES;
> > > - to_write -= wbc->nr_to_write;
> > >
> > > + to_write -= wbc->nr_to_write;
> > > ret = mpage_da_writepages(mapping, wbc, ext4_da_get_block_write);
> > > ext4_journal_stop(handle);
> > > - to_write +=wbc->nr_to_write;
> > > + if (wbc->nr_to_write) {
> > > + /* We failed to write what we requested for */
> > > + to_write += wbc->nr_to_write;
> > > + break;
> > > + }
> >
> > Not sure about the break here...
> > > + wbc->nr_to_write = to_write;
> >
> > Looks right. thanks.
> >
> > > }
> > > -
> > > out_writepages:
> > > wbc->nr_to_write = to_write;
> > > wbc->range_cyclic = range_cyclic;
> >
>
> The call chain that made me look at this was
>
> #0 ext4_da_writepages (mapping=0xc76dc244, wbc=0xc790bf70) at fs/ext4/inode.c:1557
> #1 0xc0150176 in do_writepages (mapping=0xc76dc244, wbc=0xc790bf70) at mm/page-writeback.c:1004
> #2 0xc0180fe6 in __writeback_single_inode (inode=0xc76dc11c, wbc=0xc790bf70) at fs/fs-writeback.c:285
> #3 0xc018146c in sync_sb_inodes (sb=0xc7abac00, wbc=0xc790bf70) at fs/fs-writeback.c:502
> #4 0xc0181701 in writeback_inodes (wbc=0xc790bf70) at fs/fs-writeback.c:570
> #5 0xc01509f8 in background_writeout (_min_pages=<value optimized out>) at mm/page-writeback.c:639
> #6 0xc0150f57 in pdflush (dummy=<value optimized out>) at mm/pdflush.c:127
> #7 0xc01324af in kthread (_create=<value optimized out>) at kernel/kthread.c:79
> #8 0xc0104633 in kernel_thread_helper () at include/asm/string_32.h:238
>
> ext4_da_writepages gets called with nr_to_write MAX_WRITEBACK_PAGES. the
> file size is only 4K. ie there is only one page to write. With these
> value we get stuck in the above loop because to_write will never decrement
> below 1023.
>
Ah, So I guess the comment should be reflect that the nr_to_write
returned after mpage_da_writepages() means there is no more dirty page
need to flush, then quit the loop.
Mingming
>
> -aneesh
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