Re: Strange memory usage reporting

Re: Strange memory usage reporting

[Ingo Oeser]

Hi,

On Tue, Aug 26, 2003 at 06:03:14PM +0100, Hugh Dickins wrote:
> Which is the driver involved?  Though it's not wrong to give do_no_page
> a Reserved page, beware of the the page->count accounting: while it's
> Reserved, get_page or page_cache_get raises the count, but put_page
> or page_cache_release does not decrement it - very easy to end up
> with the page never freed.

Why is this so asymetric? I would understand ignoring these pages
in the freeing logic, but why exclude them also from refcounting?

Regards

Ingo Oeser
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Re: Strange memory usage reporting

[Hugh Dickins]

On Wed, 27 Aug 2003, Ingo Oeser wrote:
> On Tue, Aug 26, 2003 at 06:03:14PM +0100, Hugh Dickins wrote:
> > Which is the driver involved?  Though it's not wrong to give do_no_page
> > a Reserved page, beware of the the page->count accounting: while it's
> > Reserved, get_page or page_cache_get raises the count, but put_page
> > or page_cache_release does not decrement it - very easy to end up
> > with the page never freed.
> 
> Why is this so asymetric? I would understand ignoring these pages
> in the freeing logic, but why exclude them also from refcounting?

I don't think there's a _good_ reason, it just evolved that way.

The real answer is to get rid of PageReserved completely, which
I'll embark on again in 2.7 (I did start a couple of times in 2.5,
but each time it was too late).

There was a halfway-house suggestion in 2.5 about three months ago,
inspired (as usual) by Reserved page problems in AIO's get_user_pages,
to do as you suggest: submit them to normal refcounting.  I don't
know what became of that, I didn't have much time to get involved.

Hugh

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