On Mon, 25 Sep 2000, Linus Torvalds wrote:
> On Mon, 25 Sep 2000, Rik van Riel wrote:
> >
> > Hmmm, doesn't GFP_BUFFER simply imply that we cannot
> > allocate new buffer heads to do IO with??
>
> No.
>
> New buffer heads would be ok - recursion is fine in theory, as long as it
> is bounded, and we might bound it some other way (I don't think we
> _should_ do recursion here due to the stack limit, but at least it's not
> a fundamental problem).
>
> The fundamental problem is that GFP_BUFFER allocations are often done with
> some critical filesystem lock held. Which means that we cannot call down
> to the filesystem to free up memory.
>
> The name is a misnomer, partly due to historical reasons (the buffer cache
> used to be fragile, and if you free'd buffer cache pages while you were
> trying to allocate new ones you could cause BadThings(tm) to happen), but
> partly just because the only _user_ of it is the buffer cache.
>
> In theory, filesystems could use it for any other allocations that they
> do, but in practice they don't, and the only allocations they do in
> critical regions is the buffer allocation. And as this thread has
> discussed, even that is really more of a bug than a feature.
Good thing to have this documented ;)
Rik
--
"What you're running that piece of shit Gnome?!?!"
-- Miguel de Icaza, UKUUG 2000
http://www.conectiva.com/ http://www.surriel.com/
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