Re: [patch] hugetlb: fix i_blocks accounting

[aglitke <agl@us.ibm.com>]

Thanks for that explanation.  It makes complete sense to me now.

On Fri, 2007-11-09 at 09:42 -0800, Ken Chen wrote:
> On Nov 9, 2007 6:17 AM, aglitke <agl@us.ibm.com> wrote:
> > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > > index 770dbed..65371bd 100644
> > > --- a/include/linux/hugetlb.h
> > > +++ b/include/linux/hugetlb.h
> > > @@ -168,6 +168,8 @@ struct file *hugetlb_file_setup(const char *name, size_t);
> > >  int hugetlb_get_quota(struct address_space *mapping, long delta);
> > >  void hugetlb_put_quota(struct address_space *mapping, long delta);
> > >
> > > +#define BLOCKS_PER_HUGEPAGE  (HPAGE_SIZE / 512)
> >
> > Sorry if this is an obvious question, but where does 512 above come
> > from?
> 
> out of stat(2) man page:
> 
> The st_blocks field indicates the number of blocks allocated to the
> file,  512-byte
> units.   (This  may  be  smaller  than  st_size/512, for example, when
> the file has
> holes.)
> 
> I looked at what other fs do with the i_blocks field (ext2, tmpfs),
> they all follow the above convention, regardless what the underlying
> fs block size is or arch page size.
> 
> > Is this just establishing a new convention that a block is equal
> > to 1/512th of whatever size a huge page happens to be?
> 
> I'm trying to be consistent with other fs.
> 
> > What about on
> > ia64 where the hugepage size is set at boot?  Wouldn't that be confusing
> > to have the block size change between boots?  What if we just make the
> > block size equal to PAGE_SIZE (which is a more stable quantity)?
> 
> It shouldn't matter, as there is another field st_blksize which
> indicate block size for the filesystem.  i_blocks is just an
> accounting on number of blocks allocated and it appears to me that it
> was intentionally set to 512 byte unit in the man page (to cut down
> confusion?  I have no idea).
> 
> - Ken
> 
-- 
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>