On Thu, 11 Apr 2013, Jan Kara wrote:
> On Tue 09-04-13 11:14:19, Lukas Czerner wrote:
> > This commit changes truncate_inode_pages_range() so it can handle non
> > page aligned regions of the truncate. Currently we can hit BUG_ON when
> > the end of the range is not page aligned, but we can handle unaligned
> > start of the range.
> >
> > Being able to handle non page aligned regions of the page can help file
> > system punch_hole implementations and save some work, because once we're
> > holding the page we might as well deal with it right away.
> >
> > In previous commits we've changed ->invalidatepage() prototype to accept
> > 'length' argument to be able to specify range to invalidate. No we can
> > use that new ability in truncate_inode_pages_range().
> >
> > Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> > ---
> > mm/truncate.c | 104 ++++++++++++++++++++++++++++++++++++++++-----------------
> > 1 files changed, 73 insertions(+), 31 deletions(-)
> >
> > diff --git a/mm/truncate.c b/mm/truncate.c
> > index fdba083..e2e8a8a 100644
> > --- a/mm/truncate.c
> > +++ b/mm/truncate.c
...
> >
> > pagevec_init(&pvec, 0);
> > index = start;
> > - while (index <= end && pagevec_lookup(&pvec, mapping, index,
> > - min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
> > + while (index < end && pagevec_lookup(&pvec, mapping, index,
> > + min(end - index, (pgoff_t)PAGEVEC_SIZE))) {
> So does this really work when end == -1 and file has ULONG_MAX pages?
> Previously it did but now you seem of skip the last page... Otherwise the
> patch looks good to me.
Recalling earlier discussion of truncate.c (which is indeed schizophrenic
about it), I believe that MAX_LFS_FILESIZE (and in particular that "-1")
prevents a file from having more than LONG_MAX pages on any architecture:
#if BITS_PER_LONG==32
#define MAX_LFS_FILESIZE (((loff_t)PAGE_CACHE_SIZE << (BITS_PER_LONG-1))-1)
#elif BITS_PER_LONG==64
#define MAX_LFS_FILESIZE ((loff_t)0x7fffffffffffffffLL)
#endif
(And if we ever extend that 32-bit range, I would recommend avoiding
the final wrap-around page, which could easily cause trouble elsewhere.)
Hugh
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