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SubjectRe: [RESEND][PATCH 5/6] Provide a filesystem-specific sync'able page bit

> > +#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.

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