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    SubjectRe: [PATCH] mm: consider all swapped back pages in used-once logic
    On Thu 17-05-12 13:23:24, Andrew Morton wrote:
    > On Thu, 17 May 2012 14:10:49 +0200
    > Michal Hocko <mhocko@suse.cz> wrote:
    >
    > > > > This patch fixes a regression introduced by this commit for heavy shmem
    > > >
    > > > A performance regression, specifically.
    > > >
    > > > Are you able to quantify it?
    > >
    > > The customer's workload is shmem backed database (80% of RAM) and
    > > they are measuring transactions/s with an IO in the background (20%).
    > > Transactions touch more or less random rows in the table.
    > > The rate goes down drastically when we start swapping out memory.
    > >
    > > Numbers are more descriptive (without the patch is 100%, with 5
    > > representative runs)
    > > Average rate 315.83%
    > > Best rate 131.76%
    > > Worst rate 641.25%
    > >
    > > Standard deviation (calibrated to average) is ~4% while without the
    > > patch we are at 62.82%.
    > > The big variance without the patch is caused by the excessive swapping
    > > which doesn't occur with the patch applied.
    > >
    > > * Worst run (100%) compared to a random run with the patch
    > > pgpgin pswpin pswpout pgmajfault
    > > 1.58% 0.00% 0.01% 0.22%
    > >
    > > Average size of the LRU lists:
    > > nr_inactive_anon nr_active_anon nr_inactive_file nr_active_file
    > > 52.91% 7234.72% 249.39% 126.64%
    > >
    > > * Best run
    > > pgpgin pswpin pswpout pgmajfault
    > > 3.37% 0.00% 0.11% 0.39%
    > >
    > > nr_inactive_anon nr_active_anon nr_inactive_file nr_active_file
    > > 49.85% 3868.74% 175.03% 121.27%
    >
    > I turned the above into this soundbite:
    >
    > : The customer's workload is shmem backed database (80% of RAM) and they are
    > : measuring transactions/s with an IO in the background (20%). Transactions
    > : touch more or less random rows in the table. Total runtime was
    > : approximately tripled by commit 64574746 and this patch restores the
    > : previous throughput levels.
    >
    > Was that truthful?

    Total runtime was same for all the runs. It is the number of executed
    transactions that was measured. I guess that what you wrote should be
    more or less equivalent but it's is not what I have numbers for.
    How about:
    "
    Total number of transactions went down 3 times (in the worst case)
    because of commit 64574746. This patch restores the previous numbers.
    "

    Thanks
    --
    Michal Hocko
    SUSE Labs
    SUSE LINUX s.r.o.
    Lihovarska 1060/12
    190 00 Praha 9
    Czech Republic


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