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Date: Thu, 11 Apr 2013 15:40:21 -0700 (PDT) From: Hugh Dickins <hughd@...gle.com> To: Jan Kara <jack@...e.cz> cc: Lukas Czerner <lczerner@...hat.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCH v3 10/18] mm: teach truncate_inode_pages_range() to handle non page aligned ranges 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@...hat.com> > > Cc: Andrew Morton <akpm@...ux-foundation.org> > > Cc: Hugh Dickins <hughd@...gle.com> > > --- > > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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