lkml.org 
[lkml]   [2008]   [Jun]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH -mm 13/25] Noreclaim LRU Infrastructure
On Sun, 8 Jun 2008 13:57:04 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> > > > From: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
> >
> > > > The noreclaim infrastructure is enabled by a new mm Kconfig option
> > > > [CONFIG_]NORECLAIM_LRU.
> > >
> > > Having a config option for this really sucks, and needs extra-special
> > > justification, rather than none.
> >
> > I believe the justification is that it uses a page flag.
> >
> > PG_noreclaim would be the 20th page flag used, meaning there are
> > 4 more free if 8 bits are used for zone and node info, which would
> > give 6 bits for NODE_SHIFT or 64 NUMA nodes - probably overkill
> > for 32 bit x86.
> >
> > If you want I'll get rid of CONFIG_NORECLAIM_LRU and make everything
> > just compile in always.
>
> Seems unlikely to be useful? The only way in which this would be an
> advantage if if we hae some other feature which also needs a page flag
> but which will never be concurrently enabled with this one.
>
> > Please let me know what your preference is.
>
> Don't use another page flag?

I don't see how that would work. We need a way to identify
the status of the page.

> > > > +#ifdef CONFIG_NORECLAIM_LRU
> > > > + PG_noreclaim, /* Page is "non-reclaimable" */
> > > > +#endif
> > >
> > > I fear that we're messing up the terminology here.
> > >
> > > Go into your 2.6.25 tree and do `grep -i reclaimable */*.c'. The term
> > > already means a few different things, but in the vmscan context,
> > > "reclaimable" means that the page is unreferenced, clean and can be
> > > stolen. "reclaimable" also means a lot of other things, and we just
> > > made that worse.
> > >
> > > Can we think of a new term which uniquely describes this new concept
> > > and use that, rather than flogging the old horse?
> >
> > Want to reuse the BSD term "pinned" instead?
>
> mm, "pinned" in Linuxland means "someone took a ref on it to prevent it
> from being reclaimed".
>
> As a starting point: what, in your english-language-paragraph-length
> words, does this flag mean?

"Cannot be reclaimed because someone has it locked in memory
through mlock, or the page belongs to something that cannot
be evicted like ramfs."

--
All rights reversed.


\
 
 \ /
  Last update: 2008-06-08 23:35    [from the cache]
©2003-2011 Jasper Spaans