On 08/04/2011 08:25 AM, Ted Ts'o wrote:
On Thu, Aug 04, 2011 at 12:22:58AM -0700, Allison Henderson wrote:
Oh, I think we do avoid calling the unmap for this last condition
though. The first and last page offsets are calculated earlier for
calling truncate_inode_pages_range to release all the pages in the
hole. The idea is that everything from first_page_offset to
last_page_offset covers all the page aligned pages in the hole. So
then if offset and length are aligned, we basically end up with
first_page_offset = offset and last_page_offset = offset + length,
and the page_len will turn out to be zero. Right math? Maybe we
can add some comments or something to help clarify.
Yeah, sorry, I wasn't clear enough about the condition. Consider the
situation where we punch the region:
4092 -- 8197
In the previous section of code, we would zero out the byte ranges
4092--4095 and 8192--8197. What's left is a completely page-aligned
range, which would have already been taken care of already. But since
we're calculating based on offsets, I believe there will be an
unnecessary call to ext4_unmap_page_range().
Oh I see, that makes sense now :) I will add in something to check for
that condition.
BTW, the name ext4_unmap_page_range() is a bit confusing; maybe we
should rename it to ext4_unmap_partial_page_buffers()?
I know you were copying from the ext4_block_zero_page_range() function
and its calling sequence (but in my opinion that function wasn't named
well and the comments in that code aren't good either).
I also wonder why we can't fold the functionality found in
ext4_unmap_page_range() into ext4_block_zero_page_range(). Did you
look into that option?
Yes, an earlier version of this patch looked a lot like that. (It was
reviewed on an internal list before it came to the ext4 list, but I keep
the version numbers so that people on both lists dont get confused). I
guess it's just a question of whether people would prefer one complex
function or two simple functions. I will send v2 to the ext4 list so
that people can get an idea of what the complex version looks like.
I do think ext4_unmap_partial_page_buffers is probably a more
descriptive name though. If we choose to keep it as a separate function,
I will add that in.
Allison Henderson
Regards,
- Ted
--
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
