linux-kernel - Re: PERF: performance tests with the split LRU VM in -mm

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Date:	Mon, 28 Jul 2008 20:31:08 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: PERF: performance tests with the split LRU VM in -mm

On Mon, 28 Jul 2008 17:17:28 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

>         /*
> -        * 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

If the active list is so small that nr_active_file >> priority always
evaluates to 0, I suspect it won't hurt at all to keep it around.

After all, we now only scan once the (incrementing) scan number reaches
swap_cluster_max.

> -        * `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?

I believe it is possible, but harmless.  Maybe even desired.

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

I'll take a look later.  Time to drive home and eat dinner :)

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