Messages in this thread | | | Date | Sun, 8 Jun 2008 13:57:04 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH -mm 13/25] Noreclaim LRU Infrastructure |
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On Sun, 8 Jun 2008 16:34:13 -0400 Rik van Riel <riel@redhat.com> wrote:
> On Fri, 6 Jun 2008 18:05:06 -0700 > Andrew Morton <akpm@linux-foundation.org> wrote: > > On Fri, 06 Jun 2008 16:28:51 -0400 > > Rik van Riel <riel@redhat.com> 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?
> > > --- linux-2.6.26-rc2-mm1.orig/include/linux/page-flags.h 2008-05-29 16:21:04.000000000 -0400 > > > +++ linux-2.6.26-rc2-mm1/include/linux/page-flags.h 2008-06-06 16:05:15.000000000 -0400 > > > @@ -94,6 +94,9 @@ enum pageflags { > > > PG_reclaim, /* To be reclaimed asap */ > > > PG_buddy, /* Page is free, on buddy lists */ > > > PG_swapbacked, /* Page is backed by RAM/swap */ > > > +#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?
> > > +/** > > > + * add_page_to_noreclaim_list > > > + * @page: the page to be added to the noreclaim list > > > + * > > > + * Add page directly to its zone's noreclaim list. To avoid races with > > > + * tasks that might be making the page reclaimble while it's not on the > > > + * lru, we want to add the page while it's locked or otherwise "invisible" > > > + * to other tasks. This is difficult to do when using the pagevec cache, > > > + * so bypass that. > > > + */ > > > > How does a task "make a page reclaimable"? munlock()? fsync()? > > exit()? > > > > Choice of terminology matters... > > Lee? Kosaki-san?
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