From: David Howells <dhowells@redhat.com>
In-Reply-To: <20041014194421.GU16153@parcelfarce.linux.theplanet.co.uk> 
References: <20041014194421.GU16153@parcelfarce.linux.theplanet.co.uk>  <24461.1097780707@redhat.com> 
To: Matthew Wilcox <matthew@wil.cx>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
       linux-fsdevel@vger.kernel.org
Subject: Re: [RESEND][PATCH 5/6] Provide a filesystem-specific sync'able page bit 
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Date: Fri, 15 Oct 2004 16:14:46 +0100
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> > +#define PG_fs_misc		 9	/* Filesystem specific bit */
> ...
> That's not really enough documentation.  Who sets this flag?  Who clears this
> flag?

That's up to the owning filesystem (or device file, I suppose); hence
"filesystem-specific". I could expand this a little, but there isn't much to
say - it's entirely up to the filesystem, though I think I should probably
require it to be cleared before the page is freed.

> Currently, mm/page_alloc.c clears this flag:

Not really; that's irrelevant. It checks to see if it is set when it allocates
a page, and if it is it complains bitterly. It then splats this bit and all
others to make sure struct page has all its flags in the ground state.

> If you're going to not kill this flag, at least rename it so we don't
> have two defines for the same bit.

I did have it as a different number, but I was told to make it the same as
PG_checked. I could rename all instances of PG_checked, I suppose...

> which really ought to at least mention Documentation/cachetlb.txt

Fix it then.

David
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