On Tue, Aug 21, 2012 at 12:54:52PM +0800, Jie Liu wrote:
> On 08/20/12 23:31, Mark Tinguely wrote:
> > On 08/13/12 08:07, Jeff Liu wrote:
> >> helper routine to lookup data or hole offset from page cache for
> >> unwritten extents.
> >>
> >> Signed-off-by: Jie Liu<jeff.liu@xxxxxxxxxx>
> >>
> >> ---
> >> fs/xfs/xfs_file.c | 213
> >> +++++++++++++++++++++++++++++++++++++++++++++++++++++
> >> 1 files changed, 213 insertions(+), 0 deletions(-)
> >> +STATIC bool
> >> +xfs_find_get_desired_pgoff(
> >> + struct inode *inode,
> >> + struct xfs_bmbt_irec *map,
> >> + unsigned int type,
> >> + loff_t *offset)
> >> +{
> >
> > ...
> >
> >> + for (i = 0; i< nr_pages; i++) {
> >> + struct page *page = pvec.pages[i];
> >> + loff_t b_offset;
> >> +
> >> + /*
> >> + * Page index is out of range, searching done.
> >> + * If the current offset is not reaches the end
> >> + * of the specified search range, there should
> >> + * be a hole between them.
> >> + */
> >> + if (page->index> end) {
> >
> > Shouldn't this sample of the index also be locked?
> Thanks for the review. Yes, it should be locked in concert with the
> sample of index below.
>
> However, as I have mentioned at v6,
> http://oss.sgi.com/archives/xfs/2012-08/msg00028.html
> I really don't understand why page->index will be changed as those pages
> returned from pagevec_lookup() should
> have refcount > 0. Hence, those pages can not be removed out of VM
> cache upon memory reclaim IMHO.
Ah, true, you are right. It's been a while since I looked at the
reference count vs truncate vs page locks in detail, and I have
always tended to err on the side of caution. I'd suggest you need to
copy the comment from write_cache_pages() here to remind us why it
is safe to do the check unlocked, otherwise in a couple of years
time someone will be asking themselves why this is safe... :/
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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