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    SubjectRe: [RFC PATCH 0/5] Improve hugepage allocation success rates under load V3
    On 08/09/2012 02:46 PM, Mel Gorman wrote:
    > On Thu, Aug 09, 2012 at 12:16:35PM -0600, Jim Schutt wrote:
    >> On 08/09/2012 07:49 AM, Mel Gorman wrote:
    >>> Changelog since V2
    >>> o Capture !MIGRATE_MOVABLE pages where possible
    >>> o Document the treatment of MIGRATE_MOVABLE pages while capturing
    >>> o Expand changelogs
    >>>
    >>> Changelog since V1
    >>> o Dropped kswapd related patch, basically a no-op and regresses if fixed (minchan)
    >>> o Expanded changelogs a little
    >>>
    >>> Allocation success rates have been far lower since 3.4 due to commit
    >>> [fe2c2a10: vmscan: reclaim at order 0 when compaction is enabled]. This
    >>> commit was introduced for good reasons and it was known in advance that
    >>> the success rates would suffer but it was justified on the grounds that
    >>> the high allocation success rates were achieved by aggressive reclaim.
    >>> Success rates are expected to suffer even more in 3.6 due to commit
    >>> [7db8889a: mm: have order> 0 compaction start off where it left] which
    >>> testing has shown to severely reduce allocation success rates under load -
    >>> to 0% in one case. There is a proposed change to that patch in this series
    >>> and it would be ideal if Jim Schutt could retest the workload that led to
    >>> commit [7db8889a: mm: have order> 0 compaction start off where it left].
    >>
    >> On my first test of this patch series on top of 3.5, I ran into an
    >> instance of what I think is the sort of thing that patch 4/5 was
    >> fixing. Here's what vmstat had to say during that period:
    >>
    >> <SNIP>
    >
    > My conclusion looking at the vmstat data is that everything is looking ok
    > until system CPU usage goes through the roof. I'm assuming that's what we
    > are all still looking at.

    I'm concerned about both the high CPU usage as well as the
    reduction in write-out rate, but I've been assuming the latter
    is caused by the former.

    <snip>

    >
    > Ok, this is an untested hack and I expect it would drop allocation success
    > rates again under load (but not as much). Can you test again and see what
    > effect, if any, it has please?
    >
    > ---8<---
    > mm: compaction: back out if contended
    >
    > ---

    <snip>

    Initial testing with this patch looks very good from
    my perspective; CPU utilization stays reasonable,
    write-out rate stays high, no signs of stress.
    Here's an example after ~10 minutes under my test load:

    2012-08-09 16:26:07.550-06:00
    vmstat -w 4 16
    procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu-------
    r b swpd free buff cache si so bi bo in cs us sy id wa st
    21 19 0 351628 576 37835440 0 0 17 44394 1241 653 6 20 64 9 0
    11 11 0 365520 576 37893060 0 0 124 2121508 203450 170957 12 46 25 17 0
    13 16 0 359888 576 37954456 0 0 98 2185033 209473 171571 13 44 25 18 0
    17 15 0 353728 576 38010536 0 0 89 2170971 208052 167988 13 43 26 18 0
    17 16 0 349732 576 38048284 0 0 135 2217752 218754 174170 13 49 21 16 0
    43 13 0 343280 576 38046500 0 0 153 2207135 217872 179519 13 47 23 18 0
    26 13 0 350968 576 37937184 0 0 147 2189822 214276 176697 13 47 23 17 0
    4 12 0 350080 576 37958364 0 0 226 2145212 207077 172163 12 44 24 20 0
    15 13 0 353124 576 37921040 0 0 145 2078422 197231 166381 12 41 30 17 0
    14 15 0 348964 576 37949588 0 0 107 2020853 188192 164064 12 39 30 20 0
    21 9 0 354784 576 37951228 0 0 117 2148090 204307 165609 13 48 22 18 0
    36 16 0 347368 576 37989824 0 0 166 2208681 216392 178114 13 47 24 16 0
    28 15 0 300656 576 38060912 0 0 164 2181681 214618 175132 13 45 24 18 0
    9 16 0 295484 576 38092184 0 0 153 2156909 218993 180289 13 43 27 17 0
    17 16 0 346760 576 37979008 0 0 165 2124168 198730 173455 12 44 27 18 0
    14 17 0 360988 576 37957136 0 0 142 2092248 197430 168199 12 42 29 17 0

    I'll continue testing tomorrow to be sure nothing
    shows up after continued testing.

    If this passes your allocation success rate testing,
    I'm happy with this performance for 3.6 - if not, I'll
    be happy to test any further patches.

    I really appreciate getting the chance to test out
    your patchset.

    Thanks -- Jim



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