On Wednesday 17 October 2007 20:30, Eric W. Biederman wrote:
quoted text
> Nick Piggin <nickpiggin@yahoo.com.au> writes:
> > On Tuesday 16 October 2007 18:08, Nick Piggin wrote:
> >> On Tuesday 16 October 2007 14:57, Eric W. Biederman wrote:
> >> > > What magic restrictions on page allocations? Actually we have
> >> > > fewer restrictions on page allocations because we can use
> >> > > highmem!
> >> >
> >> > With the proposed rewrite yes.
> >
> > Here's a quick first hack...
> >
> > Comments?
>
> I have beaten my version of this into working shape, and things
> seem ok.
>
> However I'm beginning to think that the real solution is to remove
> the dependence on buffer heads for caching the disk mapping for
> data pages, and move the metadata buffer heads off of the block
> device page cache pages.  Although I am just a touch concerned
> there may be an issue with using filesystem tools while the
> filesystem is mounted if I move the metadata buffer heads.
>
> If we were to move the metadata buffer heads (assuming I haven't
> missed some weird dependency) then I think there a bunch of
> weird corner cases that would be simplified.

I'd prefer just to go along the lines of what I posted. It's
a pure block device driver which knows absolutely nothing about
vm or vfs.

What are you guys using rd for, and is it really important to
have this supposed buffercache optimisation?


quoted text
> I guess that is where I look next.
>
> Oh for what it is worth I took a quick look at fsblock and I don't think
> struct fsblock makes much sense as a block mapping translation layer for
> the data path where the current page caches works well.

Except the page cache doesn't store any such translation. fsblock
works very nicely as a buffer_head and nobh-mode replacement there,
but we could probably go one better (for many filesystems) by using
a tree.


quoted text
> For less 
> then the cost of 1 fsblock I can cache all of the translations for a
> 1K filesystem on a 4K page.

I'm not exactly sure what you mean, unless you're talking about an
extent based data structure. fsblock is fairly slim as far as a
generic solution goes. You could probably save 4 or 8 bytes in it,
but I don't know if it's worth the trouble.


quoted text
> I haven't looked to see if fsblock makes sense to use as a buffer head
> replacement yet.

Well I don't want to get too far off topic on the subject of fsblock,
and block mappings (because I think the ramdisk driver simply should
have nothing to do with any of that)... but fsblock is exactly a
buffer head replacement (so if it doesn't make sense, then I've
screwed something up badly! ;))
-
unsubscribe notice
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/