On Thu, 7 Feb 2013, Andrew Morton wrote: > Date: Thu, 7 Feb 2013 15:40:42 -0800 > From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > To: Lukas Czerner <lczerner@xxxxxxxxxx> > Cc: linux-mm@xxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, > linux-fsdevel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, > Hugh Dickins <hughd@xxxxxxxxxx> > 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@xxxxxxxxxx> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
