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    SubjectRe: [PATCH 5/7] mm: vmscan: Do not writeback filesystem pages in kswapd except in high priority
    On Thu, Aug 11, 2011 at 06:10:29PM +0900, KAMEZAWA Hiroyuki wrote:
    > On Wed, 10 Aug 2011 11:47:18 +0100
    > Mel Gorman <mgorman@suse.de> wrote:
    >
    > > It is preferable that no dirty pages are dispatched for cleaning from
    > > the page reclaim path. At normal priorities, this patch prevents kswapd
    > > writing pages.
    > >
    > > However, page reclaim does have a requirement that pages be freed
    > > in a particular zone. If it is failing to make sufficient progress
    > > (reclaiming < SWAP_CLUSTER_MAX at any priority priority), the priority
    > > is raised to scan more pages. A priority of DEF_PRIORITY - 3 is
    > > considered to be the point where kswapd is getting into trouble
    > > reclaiming pages. If this priority is reached, kswapd will dispatch
    > > pages for writing.
    > >
    > > Signed-off-by: Mel Gorman <mgorman@suse.de>
    > > Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
    >
    >
    > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    >

    Thanks

    > BTW, I'd like to see summary of the effect of priority..
    >

    What sort of summary are you looking for? If pressure is high enough,
    writes start happening from reclaim. On NUMA, it can be particularly
    pronounced. Here is a summary of page writes from reclaim over a range
    of tests

    512M1P-xfs Page writes file fsmark 8113 74
    512M1P-xfs Page writes file simple-wb 19895 1
    512M1P-xfs Page writes file mmap-strm 997 95
    512M-xfs Page writes file fsmark 12071 9
    512M-xfs Page writes file simple-wb 31709 1
    512M-xfs Page writes file mmap-strm 148274 2448
    512M-4X-xfs Page writes file fsmark 12828 0
    512M-4X-xfs Page writes file simple-wb 32168 5
    512M-4X-xfs Page writes file mmap-strm 346460 4405
    512M-16X-xfs Page writes file fsmark 11566 29
    512M-16X-xfs Page writes file simple-wb 31935 4
    512M-16X-xfs Page writes file mmap-strm 38085 4371

    With 1 processor (512M1P), very few writes occur as for the most part
    flushers are keeping up. With 4x times more processors than there are
    CPUs (512M-4X), there are more writes by kswapd..

    1024M1P-xfs Page writes file fsmark 3446 1
    1024M1P-xfs Page writes file simple-wb 11697 6
    1024M1P-xfs Page writes file mmap-strm 4077 446
    1024M-xfs Page writes file fsmark 5159 0
    1024M-xfs Page writes file simple-wb 12785 5
    1024M-xfs Page writes file mmap-strm 251153 8108
    1024M-4X-xfs Page writes file fsmark 4781 0
    1024M-4X-xfs Page writes file simple-wb 12486 6
    1024M-4X-xfs Page writes file mmap-strm 1627122 15000
    1024M-16X-xfs Page writes file fsmark 3777 1
    1024M-16X-xfs Page writes file simple-wb 11856 2
    1024M-16X-xfs Page writes file mmap-strm 6563 2638
    4608M1P-xfs Page writes file fsmark 1497 0
    4608M1P-xfs Page writes file simple-wb 4305 0
    4608M1P-xfs Page writes file mmap-strm 17586 10153
    4608M-xfs Page writes file fsmark 3380 0
    4608M-xfs Page writes file simple-wb 5528 0
    4608M-4X-xfs Page writes file fsmark 4650 0
    4608M-4X-xfs Page writes file simple-wb 5621 0
    4608M-4X-xfs Page writes file mmap-strm 149751 18395
    4608M-16X-xfs Page writes file fsmark 388 0
    4608M-16X-xfs Page writes file simple-wb 5466 0
    4608M-16X-xfs Page writes file mmap-strm 3349772 19307

    This is the same type of tests just with more memory. If enough
    processes are running, kswapd will start writing pages as it tries
    to reclaim memory.

    4096M8N-xfs Page writes file fsmark 11571 8163
    4096M8N-xfs Page writes file simple-wb 28979 11460
    4096M8N-xfs Page writes file mmap-strm 178999 12181
    4096M8N-4X-xfs Page writes file fsmark 14421 7487
    4096M8N-4X-xfs Page writes file simple-wb 26474 10529
    4096M8N-4X-xfs Page writes file mmap-strm 163770 58765
    4096M8N-16X-xfs Page writes file fsmark 16726 9265
    4096M8N-16X-xfs Page writes file simple-wb 28800 11129
    4096M8N-16X-xfs Page writes file mmap-strm 73303 48267

    This is with 8 NUMA nodes, each 512M in size. As the flusher threads are
    not targetting a specific ndoe, kswapd writing pages happens more
    frequently.

    Is this what you are looking for?

    --
    Mel Gorman
    SUSE Labs


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