linux-kernel - Re: [Tux3] Tux3 report: Tux3 Git tree available

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: <200903162114.14460.nickpiggin@yahoo.com.au>
Date:	Mon, 16 Mar 2009 21:14:13 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Theodore Tso <tytso@....edu>
Cc:	Daniel Phillips <phillips@...nq.net>,
	linux-fsdevel@...r.kernel.org, tux3@...3.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [Tux3] Tux3 report: Tux3 Git tree available

On Monday 16 March 2009 17:38:30 Theodore Tso wrote:
> Dave,
>
> It wasn't my intention to say that XFS was bad; in fact, I thought I
> was actually complementing XFS by talking about some of the advanced
> features that XFS had (many of which I have always said that ext3 has,
> and some of which ext4 still does not have, and probably never will
> have).  I stand corrected on some of the details that I got wrong.
> What I was trying to say was that *if* (and perhaps I'm
> misunderstanding fsblock) that fsblock is requiring that as soon as a
> page is dirty, fsblock requests the filesystem to assign a block
> allocation to the buffers attached to the dirty page, that this would
> spike out delayed allocation, which would be unfortunate for *both*
> ext4 and XFS.
>
> But maybe I'm misunderstanding what fsblock is doing, and there isn't
> a problem here.

Yeah, Dave's understanding of fsblock is correct. I might have stated
things confusingly... fsblock allocates the in-memory fsblock metadata
structure (~= struct buffer_head) at the time of block dirtying. It
also asks the filesystem to respond to the dirtying event appropriately.
In the case of say ext2, this means allocating a block on disk. Wheras
XFS does the delalloc/reserve thing (yes, XFS appears to be working
with fsblock well enough to get this far).

fsblock really isn't too much different to buffer_head from an abstract
capability / functionality point of view except that it is often more
strict with things where I feel it makes sense.

So for this particular example; in buffer.c, buffers do tend to be
allocated when a page is dirtied, but not always, and even when they are,
they can get reclaimed while the page is still dirty. fsblock tigtens
this up.

--
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/