Re: [PATCH prototype] [0/8] Predictive bitmaps for ELF executables

Andi Kleen
2008-03-25T07:51:07Z

On Mon, Mar 24, 2008 at 12:42:14PM -0700, Ulrich Drepper wrote:
> On Sun, Mar 23, 2008 at 10:16 PM, Nicholas Miell <nmiell@comcast.net> wrote:
> > The limit is filesystem dependent -- I think ext2/3s is something like
> > 4k total for attribute names and values per inode.
> >
> > That's more than enough space for the largest executable on my system
> > (emacs at 36788160 bytes) which would have a 1123 byte predictive bitmap
> > (plus space for the name e.g. "system.predictive_bitmap"). The bitmap
> > also could be compressed.
>
> 4k attribute means support for about 32768 pages. That's a total of
> 134MB. I think this qualifies as sufficient. Also, I assume the
> attribute limit is just a "because nobody needed more so far" limit
> and could in theory be extended.

There is still the additional seek. Large xattrs tend to be out of line
from the inode.

-Andi