Messages in this thread | | | Date | Fri, 8 Feb 2013 10:08:05 +0100 (CET) | From | Lukáš Czerner <> | Subject | Re: [PATCH v2 10/18] mm: teach truncate_inode_pages_range() to handle non page aligned ranges |
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On Thu, 7 Feb 2013, Andrew Morton wrote:
> Date: Thu, 7 Feb 2013 15:40:42 -0800 > From: Andrew Morton <akpm@linux-foundation.org> > To: Lukas Czerner <lczerner@redhat.com> > Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, > linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, > Hugh Dickins <hughd@google.com> > Subject: Re: [PATCH v2 10/18] mm: teach truncate_inode_pages_range() to handle > non page aligned ranges > > On Tue, 5 Feb 2013 10:12:03 +0100 > Lukas Czerner <lczerner@redhat.com> 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(). > > > > ... > > > > + /* > > + * 'start' and 'end' always covers the range of pages to be fully > > + * truncated. Partial pages are covered with 'partial_start' at the > > + * start of the range and 'partial_end' at the end of the range. > > + * Note that 'end' is exclusive while 'lend' is inclusive. > > + */ > > That helped ;) So the bytes to be truncated are > > (start*PAGE_SIZE + partial_start) -> (end*PAGE_SIZE + partial_end) - 1 > > yes?
The start of the range is not right, because 'start' and 'end' covers pages to be _fully_ truncated. See the while cycle and then 'if (partial_start)' condition where we search for the page (start - 1) and do_invalidate within that page.
So it should be like this:
(start*PAGE_SIZE - partial_start*(PAGE_SIZE - partial_start) -> (end*PAGE_END + partial_end) - 1
assuming that you want the range to be inclusive on both sides.
-Lukas
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