linux-kernel - Re: [RFC 0/8] Variable Order Page Cache

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20070420063257.GB6525@kernel.dk>
Date:	Fri, 20 Apr 2007 08:32:57 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	David Chinner <dgc@....com>
Cc:	Christoph Lameter <clameter@....com>, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Paul Jackson <pj@....com>, Andi Kleen <ak@...e.de>
Subject: Re: [RFC 0/8] Variable Order Page Cache

On Fri, Apr 20 2007, David Chinner wrote:
> > - Higher order pages in the block layer etc.
> 
> It's more drivers that we have to worry about, I think.  We don't need to
> modify bios to explicitly support compound pages. From bio.h:
> 
> /*
>  * was unsigned short, but we might as well be ready for > 64kB I/O pages
>  */
> struct bio_vec {
>         struct page     *bv_page;
>         unsigned int    bv_len;
>         unsigned int    bv_offset;
> };
> 
> So compound pages should be transparent to anything that doesn't
> look at the contents of bio_vecs....

That just means you don't have to modify the bio_vec, there's still some
work to be done. But it should not be too hard, it's mainly updating the
merging checks. And grep for where PAGE_SIZE or PAGE_CACHE_SIZE is used
in fs/bio.c include/linux/bio.h block/ll_rw_blk.c

> > The ramfs driver can be used to test higher order page cache functionality
> > (and may help troubleshoot the VM support until we get some real filesystem
> > and real devices supporting higher order pages).
> 
> I don't think it will take much to get XFS to work with a high order
> page cache and we can probably insulate the block layer initially with some
> kind of bio_add_compound_page() wrapper and some similar
> wrapper on the io completion side.

Eh no way, at least not if you want it merged. Lets not repeat the XFS
kiobuf IO disaster :-). If this is to be done and merged, it needs to be
integrated nicely with the current framework, not attached to the side.

-- 
Jens Axboe

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/