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    SubjectRe: experiences beyond 4 GB RAM with 2.4.22
    On Tuesday September 9, skraw@ithnet.com wrote:
    > Hello,
    >
    > lately I upgraded my testbox from 2 to 6 GB ram and found out some oddities I
    > would like to hear your opinions.
    > The box ran flawlessly and performant with 2 GB - was in fact a real joy.
    > After upgrading the ram and recompiling kernel 2.4.22 with support for 64 GB I
    > noticed:
    >
    > 1) nfs clients see timeouts again, like
    >
    > Sep 9 03:37:35 clienta kernel: nfs: server 192.168.1.1 not responding, still
    > trying
    > Sep 9 03:37:35 clienta kernel: nfs: server 192.168.1.1 OK
    > Sep 9 03:37:35 clienta kernel: nfs: server 192.168.1.1 not responding, still
    > trying
    > Sep 9 03:37:35 clienta kernel: nfs: server 192.168.1.1 OK
    > Sep 9 03:41:13 clienta kernel: nfs: server 192.168.1.1 not responding, still
    > trying
    > Sep 9 03:41:13 clienta kernel: nfs: server 192.168.1.1 OK
    >
    > Both are 2.4.22. 192.168.1.1 is the testbox. I saw those with 2GB, but could
    > fix it through more nfs-daemons and
    >
    > echo 2097152 >/proc/sys/net/core/rmem_max
    > echo 2097152 >/proc/sys/net/core/wmem_max
    >
    > Are these values too small for 6 GB?

    No. The values are proportional to the number of server threads, not
    the amount of RAM... and they should be un-necessary after 2.4.20
    anyway as nfsd in the kernel makes the appropriate settings.


    >
    > 2) Box is very slow, kswapd looks very active during tar of a local harddisk.
    > Interactivity is really bad. Seems vm has a high time looking for free or
    > usable pages. Compared to 2 GB the behaviour is unbelievably bad.
    >
    > 3) Network performance has a remarkable dropdown during above tar. In fact
    > doing simple pings every few minutes shows that quite a lot of them are simply
    > dropped, never make it over the ethernet.

    My only guess is that it is doing a lot of copying into low memory
    because your devices can only DMA into/outof low memory.
    Have you tried 2.6 ??
    How about CONFIG_HIGHMEM4G ?
    It won't use all the RAM, but it would be interesting if it were
    faster.

    NeilBrown
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