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    SubjectRe: PERF: performance tests with the split LRU VM in -mm
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    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@redhat.com> wrote:
    >
    > > On Mon, 28 Jul 2008 19:57:13 -0400
    > > Rik van Riel <riel@redhat.com> wrote:
    > > > On Mon, 28 Jul 2008 16:41:24 -0700
    > > > Andrew Morton <akpm@linux-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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