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    SubjectRe: [PATCHv 2] tcp: properly initialize tcp memory limits part 2 (fix nfs regression)
    On Sat, 3 Mar 2012 11:16:41 -0300
    Glauber Costa <glommer@parallels.com> wrote:

    > On 03/02/2012 02:50 PM, Sergei Trofimovich wrote:
    > >>>> The change looks like a typo (division flipped to multiplication):
    > >>>>> limit = nr_free_buffer_pages() / 8;
    > >>>>> limit = nr_free_buffer_pages()<< (PAGE_SHIFT - 10);
    > >>>
    > >>> Hi, thanks for the reporting. It's not a typo. It was previously:
    > >>> sysctl_tcp_mem[1]<< (PAGE_SHIFT - 7). Looks like we need to do the
    > >>> limit check before shift the value. Please try the following patch, thanks.
    > >>
    > >> Still does not help. I test it by checking sha1sum of a large file over NFS
    > >> (small files seem to work simetimes):
    > >>
    > >> $ strace sha1sum /gentoo/distfiles/gcc-4.6.2.tar.bz2
    > >> ...
    > >> open("/gentoo/distfiles/gcc-4.6.2.tar.bz2", O_RDONLY
    > >> <HUNG>
    > >> After a certain timeout dmesg gets odd spam:
    > >> [ 314.848094] nfs: server vmhost not responding, still trying
    > >> [ 314.848134] nfs: server vmhost not responding, still trying
    > >> [ 314.848145] nfs: server vmhost not responding, still trying
    > >> [ 314.957047] nfs: server vmhost not responding, still trying
    > >> [ 314.957066] nfs: server vmhost not responding, still trying
    > >> [ 314.957075] nfs: server vmhost not responding, still trying
    > >> [ 314.957085] nfs: server vmhost not responding, still trying
    > >> [ 314.957100] nfs: server vmhost not responding, still trying
    > >> [ 314.958023] nfs: server vmhost not responding, still trying
    > >> [ 314.958035] nfs: server vmhost not responding, still trying
    > >> [ 314.958044] nfs: server vmhost not responding, still trying
    > >> [ 314.958054] nfs: server vmhost not responding, still trying
    > >>
    > >> looks like bogus messages. Might be relevant to mishandled timings
    > >> somewhere else or a bug in nfs code.
    > >
    > > And after 120 seconds hung tasks shows it might be an OOM issue
    > > Likely caused by patch, as it's a 2GB RAM +4GB swap amd64 box
    > > not running anything heavy:
    >
    > That is a bit weird.
    >
    > First because with Jason's patch, we should end up with the very same
    > calculation, at the same exact order, as it was in older kernels.
    > Second, because by shifting << 10, you should be ending up with very
    > small numbers, effectively having tcp_rmem[1] == tcp_rmem[2], and the
    > same for wmem.
    >
    > Can you share which numbers you end up with at
    > /proc/sys/net/ipv4/tcp_{r,w}mem ?
    >

    Sure:

    $ cat /proc/sys/net/ipv4/tcp_{r,w}mem
    4096 87380 1999072
    4096 16384 1999072

    Nothing special with NFS nere, so I guess it uses UDP.
    TCP works fine on machine (I do everything via SSH).

    --

    Sergei
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