linux-kernel - Re: [PATCH v1 0/3] do not use s

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Message-Id: <20120413002656.b67e58ad.akpm@linux-foundation.org>
Date:	Fri, 13 Apr 2012 00:26:56 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	dedekind1@...il.com
Cc:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Linux Kernel Maling List <linux-kernel@...r.kernel.org>,
	Linux FS Maling List <linux-fsdevel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>, Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [PATCH v1 0/3] do not use s_dirt in FAT FS

On Fri, 13 Apr 2012 09:38:28 +0300 Artem Bityutskiy <dedekind1@...il.com> wrote:

> > That implies that we retain ->write_super, probably in a modified form.
> > Modified to permit the VFS to determine whether the superblock needs
> > treatment, if ->s_dirt doesn't suffice.
> 
> I tried this approach and it was vetoed by Al Viro. Although it is
> simpler to me to resurrect my old patches, I agree with Al that killing
> '->write_super()' is a better approach.

Well, it can be done without a super_operation vector - pass the
library code a superblock* and a function address.  But the difference
is pointless fluff.

> We do not want to serve a whole
> kernel thread in the generic code for few baroque citizens.

One could refcount the thread, but I think I misread the code - the
amount of generic boilerplate which was added to the fs is in fact
pretty small.

> Please, see this thread for the reference:
> http://lkml.org/lkml/2010/7/22/96
> 
> > The code as you've proposed it will cause more wakeups than needed - if
> > multiple filesystems are mounted and active, their timers will get out
> > of sync.  Which rather defeats the intent of the whole work!  This
> > problem should be addressable via some new centralised way of managing
> > things.
> 
> I do not think this is an issue. If we have many file-systems, and all
> of them are actively used so that the super block becomes dirty, which
> most probably means there is also write-back - so be it, it is ok to arm
> many timers. And if we make them deferrable for most of the FSes (which
> we can not do for the generic timer, because we do not know FSes needs)
> - then this is not an issue at all.

OK.

> Also, if you look at this from the angle that only few old FSes will
> have this, it becomes not that bad. I assume I will change this
> patch-set and won't use delayed works here.

I don't think I understand that.  You intend to alter this patchset?
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