Message-Id: <1217292406.21495.4.camel@lts-notebook>
Date:	Mon, 28 Jul 2008 20:46:46 -0400
From:	Lee Schermerhorn <Lee.Schermerhorn@...com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: PERF: performance tests with the split LRU VM in -mm

On Mon, 2008-07-28 at 17:17 -0700, Andrew Morton wrote:
> On Mon, 28 Jul 2008 20:03:11 -0400
> Rik van Riel <riel@...hat.com> wrote:
> 
> > On Mon, 28 Jul 2008 19:57:13 -0400
> > Rik van Riel <riel@...hat.com> wrote:
> > > On Mon, 28 Jul 2008 16:41:24 -0700
> > > Andrew Morton <akpm@...ux-foundation.org> wrote:
> > > 
> > > > > Andrew, what is your preference between:
> > > > > 	http://lkml.org/lkml/2008/7/15/465
> > > > > and
> > > > > 	http://marc.info/?l=linux-mm&m=121683855132630&w=2
> > > > > 
> > > > 
> > > > Boy.  They both seem rather hacky special-cases.  But that doesn't mean
> > > > that they're undesirable hacky special-cases.  I guess the second one
> > > > looks a bit more "algorithmic" and a bit less hacky-special-case.  But
> > > > it all depends on testing..
> > > 
> > > I prefer the second one, since it removes the + 1 magic (at least,
> > > for the higher priorities), instead of adding new magic like the
> > > other patch does.
> > 
> > Btw, didn't you add that "+ 1" originally early on in the 2.6 VM?
> 
> You mean this?
> 
> 		/*
> 		 * Add one to nr_to_scan just to make sure that the kernel
> 		 * will slowly sift through the active list.
> 		 */
> 		zone->nr_scan_active +=
> 			(zone_page_state(zone, NR_ACTIVE) >> priority) + 1;
> 
> 
> > Do you remember its purpose?  
> 
> erm, not specifically, but I tended to lavishly describe changes like
> this in the changelogging.
> 
> > Does it still make sense to have that "+ 1" in the split LRU VM?
> > 
> > Could we get away with just removing it unconditionally?
> 
> We should do the necessary git dumpster-diving before tossing out
> hard-won changes.  Otherwise we might need to spend a year
> re-discovering and re-fixing already-discovered-and-fixed things.
> 
> That code has been there in one way or another for some time.
> 
> In June 2004, 385c0449 did this:
> 
>         /*
> -        * Try to keep the active list 2/3 of the size of the cache.  And
> -        * make sure that refill_inactive is given a decent number of pages.
> -        *
> -        * The "scan_active + 1" here is important.  With pagecache-intensive
> -        * workloads the inactive list is huge, and `ratio' evaluates to zero
> -        * all the time.  Which pins the active list memory.  So we add one to
> -        * `scan_active' just to make sure that the kernel will slowly sift
> -        * through the active list.
> +        * Add one to `nr_to_scan' just to make sure that the kernel will
> +        * slowly sift through the active list.
>          */
> -       if (zone->nr_active >= 4*(zone->nr_inactive*2 + 1)) {
> -               /* Don't scan more than 4 times the inactive list scan size */
> -               scan_active = 4*scan_inactive;
> 
> (there was some regrettable information loss there).
> 
> Is the scenario which that fix addresses no longer possible?
> 
> 
> On a different topic, I am staring in frustration at
> introduce-__get_user_pages.patch, which says:
> 
>   New munlock processing need to GUP_FLAGS_IGNORE_VMA_PERMISSIONS. 
>   because current get_user_pages() can't grab PROT_NONE pages theresore
>   it cause PROT_NONE pages can't munlock.
> 
> could someone please work out for me which of these patches:
> 
> vmscan-move-isolate_lru_page-to-vmscanc.patch
> vmscan-use-an-indexed-array-for-lru-variables.patch
> swap-use-an-array-for-the-lru-pagevecs.patch
> vmscan-free-swap-space-on-swap-in-activation.patch
> define-page_file_cache-function.patch
> vmscan-split-lru-lists-into-anon-file-sets.patch
> vmscan-second-chance-replacement-for-anonymous-pages.patch
> vmscan-fix-pagecache-reclaim-referenced-bit-check.patch
> vmscan-add-newly-swapped-in-pages-to-the-inactive-list.patch
> more-aggressively-use-lumpy-reclaim.patch
> pageflag-helpers-for-configed-out-flags.patch
> unevictable-lru-infrastructure.patch
> unevictable-lru-page-statistics.patch
> ramfs-and-ram-disk-pages-are-unevictable.patch
> shm_locked-pages-are-unevictable.patch
> mlock-mlocked-pages-are-unevictable.patch

Andrew:  

Kosaki-san's patch to introduce __get_user_pages() is a patch to the
above unevictable, mlocked pages.  He enhanced get_user_pages() so that
we could fault in PROT_NONE pages for munlocking, to replace the page
table walker [subsequent patches in that series].  He replaced the page
table walker to avoid the "sleeping while atomic" for 32-bit/HIGHPTE
configs.

Lee

> mlock-downgrade-mmap-sem-while-populating-mlocked-regions.patch
> mmap-handle-mlocked-pages-during-map-remap-unmap.patch
> 
> that patch fixes?
> 
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